Following up on my previous post, a few more points are worth making
regarding the scientific process.
First, regarding uncertainty. Earth's atmosphere and oceans do form a
more complicated system than the simple model I described. For
example, here's one way in which it is possible that temperatures
would not rise much in response to carbon dioxide impeding the outward
flow of heat. When temperatures go up initially, that means more
water vapor in the atmosphere. If that water vapor condenses into
clouds, the extra clouds could reflect enough sunlight back into space
to reduce the heating and make temperatures fall back to normal. This
mechanism would act like a thermostat keeping Earth's surface within a
narrow temperature range, and we wouldn't need to worry about keeping
our carbon emissions in check. So, if you heard Arrhenius's warming
prediction in 1896, you could easily say, "but there's a lot of
uncertainty in that prediction because we don't understand cloud
formation. Maybe there won't be that much warming. It's uncertain."
The point I want to make is that uncertainty cuts both ways. Water
vapor is itself a greenhouse gas, so if the extra vapor does not
condense into clouds, the greenhouse warming will be accelerated.
Yes, the prediction is uncertain....but that means that more extreme
outcomes, as well as less extreme outcomes, are possible.
If a little bit of warming produces clouds which shut down further
warming, we would call that a negative feedback loop; negative because
any change contains the seeds of its own reversal. If instead a bit
of warming creates water vapor which accelerates the warming, we would
call that a positive feedback loop; positive because a little movement
encourages further movement in the same direction. One reason climate
is complicated is that it is full of feedback loops, another example
being that reduced ice coverage causes more sunlight to be absorbed,
which reduces ice coverage further, etc. So what's the verdict on the
cloud formation? We still don't know; it may depend on how much
small-particle pollution we produce, because these small particles
provide the seeds for cloud condensation. But meanwhile, temperatures
keep rising. So while we puzzle over the details, let's not forget
the big picture: we keep making Earth's carbon-dioxide blanket thicker
and thicker.
Second point: I've repeatedly stressed the important of models in terms of
understanding a system. Models are great for exploring a variety of
scenarios, but is there anything we can say about climate that does
not depend on what model we adopt? Such model-independent statements
can be valuable anchors when we're not sure which model to adopt. I'd
like to focus particularly on a (more or less) model-independent
statement regarding sea levels. We can get rid of models and just
accumulate data regarding sea levels and carbon dioxide levels in the
past, and then we can simply ask, what is the typical sea level when
the carbon dioxide level is 400 parts per million, as we have now
caused it to be? (It's up from about 275 before the Industrial
Revolution.)
The answer is shocking: 24 meters, or 80 feet! Go ahead and play with
this interactive flood map to see what such a rise will do to your
state or country.
Now I have to give a few caveats. First, changes in carbon dioxide
concentration and sea levels occurred very slowly in the past.
Although we are pumping carbon dioxide in very quickly, it's quite
likely that it will be hundreds or even a few thousand years before
the effects of the carbon input are fully realized and sea levels rise
this much. Essentially no one is predicting these sea levels within
our children's lifetimes. But still....this will be a lot for our
great-great-grandchildren to deal with. And yes, there's uncertainty on this
prediction. Sea levels may rise less than this. But they may also rise more
than this.
Second caveat: this prediction is not entirely model-independent. To
be an extreme devil's advocate, if CO2 levels in the past were somehow
a natural effect of higher sea levels rather than a cause, then we could not
use past data to predict what would happen when we artificially increase
CO2 levels today. To be clear, I invoke that scenario not because I
believe it, but simply to highlight how an apparently
model-independent statement is often not entirely
model-independent. If all kinds of crazy models are allowed into the
discussion, then very few truly model-independent statements can be
made. But within the scope of "reasonable" models, we can say that
sea levels will rise by around 24 meters; we just don't know long
that will take. Predicting how long it will take requires a model!
If you are interested in further reading, start with this Skeptical
Science post, which summarizes this publication in an approachable
way. Skeptical Science, by the way, is a good resource for rebutting
common climate myths.
Showing posts with label nature of science. Show all posts
Showing posts with label nature of science. Show all posts
Thursday, February 27, 2014
Wednesday, February 26, 2014
Climate 101
Nice article today in the New York Times: Study Links Temperature to a
Peruvian Glacier’s Growth and Retreat. It's a good example of how news
about climate change could easily be misread as indicating more doubt
than there really is. The headline makes it sound as if the link between
glaciers and temperature is so tenuous that this is the first evidence of it,
and that it has been established for only one glacier. The truth is very
different, even though the headline and article are not wrong once you
understand the context. This post is aimed at helping teachers
and students with the basics, and then use that to parse the news.
Over a century ago, it was known that carbon dioxide impedes the flow
of heat (in the form of infrared light) from the Earth out into space,
while not impeding the flow of heat (mostly in the form of visible
light) from the Sun to the Earth. If not for this natural greenhouse
effect, Earth would be much colder. Teachers can demonstrate quite
directly that carbon dioxide impedes the flow of infrared light, but
many teachers may not have the right equipment. Here's a video
comparing the temperature rise of two bottles, one with elevated
levels of carbon dioxide and the other with standard air. And here's
a nice video using an infrared camera to show quite directly that
infrared light is largely blocked by carbon dioxide.
Around the same time (1896) Svante Arrhenius recognized that humans
were pumping ever more carbon dioxide into the atmosphere, and that
this would lead to warming. But "warming" sounded reasonably
beneficial, especially given Arrhenius's prediction that it would take
place slowly over thousands of years. Arrhenius did not account for
the large increase in population over the ensuing century, nor for the
large increase in per-capita use of fossil fuels (cars, airplanes,
etc). Worldwide, we now emit about 17 times the carbon dioxide emitted
in 1896, so change is coming much faster. And now we know that an
increase in temperature is not as beneficial as it may sound because
it can radically change weather patterns, which imposes large costs on
humans as well as on many species which cannot move and adapt rapidly
enough. Apart from that, Arrhenius deserves kudos for his prescience.
Yet if we heard this prediction in 1896 we would be justified in
expressing some skepticism. Earth's atmosphere and oceans (where most
of the excess heat is deposited) form a complicated system, and the
response of a complicated system to a simple input (more heat) may
well not be a simple result (higher temperature). But healthy
skepticism goes only so far; unless you have a better model, you have
to admit that the best model predicts warming. Just saying "it's a
complicated system" does not give you the right to reject all models.
In this case, you would have to figure out where the extra heat would
go without causing increased temperatures, and you would have to have
some evidence to motivate belief in that model.
Fast forward to 2014. Warming is here, and we've learned a lot about
climate models in the meantime. We did find complications (El Nino,
for one), but the simple model was reasonable in its overall
prediction. More heat does mean a higher temperature.
One way "climate skeptics" (I put the term in quotes because
oil-company funding leads to a kind of "skepticism" different from the
detached sort of skepticism we encourage in science) sow doubt about
this result is to suggest that the warming may be due to natural
cycles. There certainly are natural climate cycles, but rather than
treat them in detail here I want to make a bigger point about how
science works: When a model makes a prediction and the prediction
comes true, we should gain confidence in the model, and we should lose
confidence in models which made contrary predictions. Yes, it's
conceivable that the greenhouse model's prediction came true through
a fluke of natural cycles rather than accurately modeling how nature works
...but how much confidence would you put on that possibility?
A prediction is a powerful thing, so let's note the distinction between
a prediction and a retrodiction (or postdiction), which is when you make a
hypothesis after looking at the data. Using data (rather than laws of
physics or other guiding principles) to generate hypotheses is a fine
thing to do, but because "patterns" can randomly appear in data you
cannot confirm the hypothesis with the same data which generated it;
you must seek out new data. (Admittedly, even scientists sometimes
forget to apply this principle.) Climate skeptics can suggest
alternative causes for the warming after looking at the data, but we
should have much more confidence in the model which actually predicted
the data.
Now, the news: a reconstruction of the timeline of growth and
shrinkage of a Peruvian glacier shows that shrinkage is most highly
correlated with temperature and not with other factors such as
precipitation. You have to get halfway through the article to get the
background:
So, you may have started reading the article thinking that scientists
understood very little about glaciers if they were just now finding a
"link" between glacier shrinkage and temperature, but you now see
that a lot of important knowledge has already been established.
Newspaper articles are designed to tell you what's new first, so it's not
the writer's fault that this background was buried deep in the article.
Nevertheless, in practice many readers will just read the headline and
skim the first part of the article, thus missing this crucial background.
Teachers and students should be aware of this when reading science news.
But wait, there's more! The article goes on to explain how the details
of tropical glaciers are different from most glaciers (intense
sunlight can vaporize the ice directly, and the sunlight lasts
year-round) but that one group of scientists has studied the matter
and still concluded that temperature is the driving factor in
shrinking tropical glaciers. "But a second group believes that in some
circumstances, at least, a tropical glacier’s long-term fate may
reflect other factors. In particular, these scientists believe big
changes in precipitation can sometimes have more of a role than
temperature." In other words, this is a legitimate scientific dispute, but
it is about the details of a very specific type of glacier and has little or
nothing to do with overall concerns about glaciers (or sea ice)
melting worldwide, much less about the reality of climate change. Yet
someone who wants to sow doubt about climate change can point to this
and say "scientists don't really understand why glaciers melt" and people
who don't read the article carefully may well be snookered by that.
Please make sure you (and, if you are a teacher, your students) don't
get snookered.
My next post discusses two more aspects of the nature of science---uncertainty
and model-independent statements---in the context of climate.
Peruvian Glacier’s Growth and Retreat. It's a good example of how news
about climate change could easily be misread as indicating more doubt
than there really is. The headline makes it sound as if the link between
glaciers and temperature is so tenuous that this is the first evidence of it,
and that it has been established for only one glacier. The truth is very
different, even though the headline and article are not wrong once you
understand the context. This post is aimed at helping teachers
and students with the basics, and then use that to parse the news.
Over a century ago, it was known that carbon dioxide impedes the flow
of heat (in the form of infrared light) from the Earth out into space,
while not impeding the flow of heat (mostly in the form of visible
light) from the Sun to the Earth. If not for this natural greenhouse
effect, Earth would be much colder. Teachers can demonstrate quite
directly that carbon dioxide impedes the flow of infrared light, but
many teachers may not have the right equipment. Here's a video
comparing the temperature rise of two bottles, one with elevated
levels of carbon dioxide and the other with standard air. And here's
a nice video using an infrared camera to show quite directly that
infrared light is largely blocked by carbon dioxide.
Around the same time (1896) Svante Arrhenius recognized that humans
were pumping ever more carbon dioxide into the atmosphere, and that
this would lead to warming. But "warming" sounded reasonably
beneficial, especially given Arrhenius's prediction that it would take
place slowly over thousands of years. Arrhenius did not account for
the large increase in population over the ensuing century, nor for the
large increase in per-capita use of fossil fuels (cars, airplanes,
etc). Worldwide, we now emit about 17 times the carbon dioxide emitted
in 1896, so change is coming much faster. And now we know that an
increase in temperature is not as beneficial as it may sound because
it can radically change weather patterns, which imposes large costs on
humans as well as on many species which cannot move and adapt rapidly
enough. Apart from that, Arrhenius deserves kudos for his prescience.
Yet if we heard this prediction in 1896 we would be justified in
expressing some skepticism. Earth's atmosphere and oceans (where most
of the excess heat is deposited) form a complicated system, and the
response of a complicated system to a simple input (more heat) may
well not be a simple result (higher temperature). But healthy
skepticism goes only so far; unless you have a better model, you have
to admit that the best model predicts warming. Just saying "it's a
complicated system" does not give you the right to reject all models.
In this case, you would have to figure out where the extra heat would
go without causing increased temperatures, and you would have to have
some evidence to motivate belief in that model.
Fast forward to 2014. Warming is here, and we've learned a lot about
climate models in the meantime. We did find complications (El Nino,
for one), but the simple model was reasonable in its overall
prediction. More heat does mean a higher temperature.
One way "climate skeptics" (I put the term in quotes because
oil-company funding leads to a kind of "skepticism" different from the
detached sort of skepticism we encourage in science) sow doubt about
this result is to suggest that the warming may be due to natural
cycles. There certainly are natural climate cycles, but rather than
treat them in detail here I want to make a bigger point about how
science works: When a model makes a prediction and the prediction
comes true, we should gain confidence in the model, and we should lose
confidence in models which made contrary predictions. Yes, it's
conceivable that the greenhouse model's prediction came true through
a fluke of natural cycles rather than accurately modeling how nature works
...but how much confidence would you put on that possibility?
A prediction is a powerful thing, so let's note the distinction between
a prediction and a retrodiction (or postdiction), which is when you make a
hypothesis after looking at the data. Using data (rather than laws of
physics or other guiding principles) to generate hypotheses is a fine
thing to do, but because "patterns" can randomly appear in data you
cannot confirm the hypothesis with the same data which generated it;
you must seek out new data. (Admittedly, even scientists sometimes
forget to apply this principle.) Climate skeptics can suggest
alternative causes for the warming after looking at the data, but we
should have much more confidence in the model which actually predicted
the data.
Now, the news: a reconstruction of the timeline of growth and
shrinkage of a Peruvian glacier shows that shrinkage is most highly
correlated with temperature and not with other factors such as
precipitation. You have to get halfway through the article to get the
background:
land ice is melting virtually everywhere on the planet...the pace seems to have accelerated substantially in recent decades as human emissions have begun to overwhelm the natural cycles. In the middle and high latitudes, from Switzerland to Alaska, a half-century of careful glaciology has established that temperature is the main factor controlling the growth and recession of glaciers. But the picture has been murkier in the tropics. There, too, glaciers are retreating, but scientists have had more trouble sorting out exactly why.
So, you may have started reading the article thinking that scientists
understood very little about glaciers if they were just now finding a
"link" between glacier shrinkage and temperature, but you now see
that a lot of important knowledge has already been established.
Newspaper articles are designed to tell you what's new first, so it's not
the writer's fault that this background was buried deep in the article.
Nevertheless, in practice many readers will just read the headline and
skim the first part of the article, thus missing this crucial background.
Teachers and students should be aware of this when reading science news.
But wait, there's more! The article goes on to explain how the details
of tropical glaciers are different from most glaciers (intense
sunlight can vaporize the ice directly, and the sunlight lasts
year-round) but that one group of scientists has studied the matter
and still concluded that temperature is the driving factor in
shrinking tropical glaciers. "But a second group believes that in some
circumstances, at least, a tropical glacier’s long-term fate may
reflect other factors. In particular, these scientists believe big
changes in precipitation can sometimes have more of a role than
temperature." In other words, this is a legitimate scientific dispute, but
it is about the details of a very specific type of glacier and has little or
nothing to do with overall concerns about glaciers (or sea ice)
melting worldwide, much less about the reality of climate change. Yet
someone who wants to sow doubt about climate change can point to this
and say "scientists don't really understand why glaciers melt" and people
who don't read the article carefully may well be snookered by that.
Please make sure you (and, if you are a teacher, your students) don't
get snookered.
My next post discusses two more aspects of the nature of science---uncertainty
and model-independent statements---in the context of climate.
Monday, September 2, 2013
"Just" a Theory?
A recently published letter to the New York Times reminds us that relativity is "just a theory" and so is the Big Bang. Scientists and science educators need to set the record straight on this "just a theory" meme any time we get a chance to discuss science with kids and grown-up nonscientists. So here's my shot at it.
A good analogy is to think of facts as being like bricks: solid and dependable, but one or a few bricks are not very useful by themselves ("an electron passed through my detector at 11:58:32.01" or "the high temperature in Davis, CA on September 1, 2013 was 96 F"). Only when we assemble lots (lots) of bricks into a coherent structure do we get the benefits of having a building (the theory of relativity, or a climate model). Not only is an isolated brick rather useless, but the building can easily survive the removal of a few bricks here and there. A good theory integrates millions or billions of observations into a coherent whole. Calling relativity "just a theory" is like calling the Great Wall of China "just a fence," the Panama Canal "just a ditch," or the Golden Gate Bridge "just a road."
There's a reason that calling the Great Wall of China "just a fence" sounds more outrageous than calling relativity "just a theory"---I used the word fence which connotes something less important than a wall. There's a rich vocabulary to describe to describe barriers: from weak to strong we might use tape, rope, cordon, railing, fence, and wall. But most people don't use a similarly rich vocabulary to describe levels of sophistication of mental models. From weak to strong I might suggest educated guess, working hypothesis, model, and theory, but most people in practice indiscriminately use the word theory for any of these. So it's our duty as scientists to make clear that well-accepted scientific theories integrate an incredible range of observations into a structure which is so coherent that it is difficult to imagine all those pieces fitting into any other structure. Maybe a better analogy to calling relativity "just a theory" is calling an assembled jigsaw puzzle "just one way to fit the pieces together."
Gotcha, the just-a-theory crowd says, by making that analogy you are showing that you are rigid in your thinking and unwilling to accept alternative explanations. Nonsense. Scientists are constantly trying to prove accepted theories wrong. Anyone who succeeds in disproving relativity, the Big Bang, or evolution will win a Nobel Prize and eternal fame, so we'd be happy to do so. But we know from experience that the most likely explanation for an isolated fact that seems to contradict relativity, the Big Bang, or evolution is that the fact itself was taken out of context or is not being properly interpreted, rather than that an extremely well-tested theory is wrong.
This doesn't mean that we will twist any fact to make it fit into our well-accepted theories. It does mean that surprising facts may end up extending the theory rather than replacing it. For example, Newton's theory of gravity explains a ton of observations about the motions of the planets and stars, but in a few extreme circumstances (such as very close to the Sun) it doesn't predict exactly what is observed. Einstein developed a theory of gravity (general relativity) which does correctly predict these situations. Einstein's theory is more complicated than Newton's, but in most situations the complicated parts of Einstein's theory have very little quantitative effect so we can simplify it a great deal and in those cases it turns out to be identical to....Newton's theory! This almost had to be the case, because Newton's theory accounted so well for so many observations that it would be hard to imagine that it was wrong rather than incomplete.
This example shows that a small number of facts can be critically important and that scientists do pay attention to facts which don't fit the theory. But we don't modify or overturn theories willy-nilly. When the planet Uranus didn't move exactly as Newton's theory predicted, modifications of the theory were considered but so was the possibility that some mass other than the Sun and the known planets was pulling on Uranus, and that led to the discovery of Neptune. If we rejected well-established theories at the first hint of any discrepancy with new observations, we would be giving undue weight to the new observations and too little weight to the vast range of previous observations explained by the theory. If you want to overthrow a theory because some new observation seems to contradict it, then give us a better theory which explains the new observation while still fitting the previous observations just as well as the old theory. That latter part seems to be conveniently forgotten by people who want to reject well-established theories.
A closely parallel situation is that of criminal investigators and prosecutors who present their "theory of the crime" to a jury. ("Model of the crime" would better fit my vocabulary hierarchy, but this is the word actually used.) A lot of facts may be introduced into evidence ("a car with the suspect's license plate was recorded crossing the Tappan Zee Bridge at 2:20am on August 31"), but by themselves they don't mean anything important. A good theory of the crime provides a coherent explanation of so many different facts that the jury is forced to conclude that it is true beyond a reasonable doubt. If you want to call it "just a theory" then offer us a different theory which fits the facts just as well. The defense is given sufficient time and strong motivation to offer a good alternative theory, so failure to present one is damning.
A good analogy is to think of facts as being like bricks: solid and dependable, but one or a few bricks are not very useful by themselves ("an electron passed through my detector at 11:58:32.01" or "the high temperature in Davis, CA on September 1, 2013 was 96 F"). Only when we assemble lots (lots) of bricks into a coherent structure do we get the benefits of having a building (the theory of relativity, or a climate model). Not only is an isolated brick rather useless, but the building can easily survive the removal of a few bricks here and there. A good theory integrates millions or billions of observations into a coherent whole. Calling relativity "just a theory" is like calling the Great Wall of China "just a fence," the Panama Canal "just a ditch," or the Golden Gate Bridge "just a road."
There's a reason that calling the Great Wall of China "just a fence" sounds more outrageous than calling relativity "just a theory"---I used the word fence which connotes something less important than a wall. There's a rich vocabulary to describe to describe barriers: from weak to strong we might use tape, rope, cordon, railing, fence, and wall. But most people don't use a similarly rich vocabulary to describe levels of sophistication of mental models. From weak to strong I might suggest educated guess, working hypothesis, model, and theory, but most people in practice indiscriminately use the word theory for any of these. So it's our duty as scientists to make clear that well-accepted scientific theories integrate an incredible range of observations into a structure which is so coherent that it is difficult to imagine all those pieces fitting into any other structure. Maybe a better analogy to calling relativity "just a theory" is calling an assembled jigsaw puzzle "just one way to fit the pieces together."
Gotcha, the just-a-theory crowd says, by making that analogy you are showing that you are rigid in your thinking and unwilling to accept alternative explanations. Nonsense. Scientists are constantly trying to prove accepted theories wrong. Anyone who succeeds in disproving relativity, the Big Bang, or evolution will win a Nobel Prize and eternal fame, so we'd be happy to do so. But we know from experience that the most likely explanation for an isolated fact that seems to contradict relativity, the Big Bang, or evolution is that the fact itself was taken out of context or is not being properly interpreted, rather than that an extremely well-tested theory is wrong.
This doesn't mean that we will twist any fact to make it fit into our well-accepted theories. It does mean that surprising facts may end up extending the theory rather than replacing it. For example, Newton's theory of gravity explains a ton of observations about the motions of the planets and stars, but in a few extreme circumstances (such as very close to the Sun) it doesn't predict exactly what is observed. Einstein developed a theory of gravity (general relativity) which does correctly predict these situations. Einstein's theory is more complicated than Newton's, but in most situations the complicated parts of Einstein's theory have very little quantitative effect so we can simplify it a great deal and in those cases it turns out to be identical to....Newton's theory! This almost had to be the case, because Newton's theory accounted so well for so many observations that it would be hard to imagine that it was wrong rather than incomplete.
This example shows that a small number of facts can be critically important and that scientists do pay attention to facts which don't fit the theory. But we don't modify or overturn theories willy-nilly. When the planet Uranus didn't move exactly as Newton's theory predicted, modifications of the theory were considered but so was the possibility that some mass other than the Sun and the known planets was pulling on Uranus, and that led to the discovery of Neptune. If we rejected well-established theories at the first hint of any discrepancy with new observations, we would be giving undue weight to the new observations and too little weight to the vast range of previous observations explained by the theory. If you want to overthrow a theory because some new observation seems to contradict it, then give us a better theory which explains the new observation while still fitting the previous observations just as well as the old theory. That latter part seems to be conveniently forgotten by people who want to reject well-established theories.
A closely parallel situation is that of criminal investigators and prosecutors who present their "theory of the crime" to a jury. ("Model of the crime" would better fit my vocabulary hierarchy, but this is the word actually used.) A lot of facts may be introduced into evidence ("a car with the suspect's license plate was recorded crossing the Tappan Zee Bridge at 2:20am on August 31"), but by themselves they don't mean anything important. A good theory of the crime provides a coherent explanation of so many different facts that the jury is forced to conclude that it is true beyond a reasonable doubt. If you want to call it "just a theory" then offer us a different theory which fits the facts just as well. The defense is given sufficient time and strong motivation to offer a good alternative theory, so failure to present one is damning.
Saturday, February 23, 2013
Get My Drift?
Yesterday we did three activities related to plate tectonics: making a
model of continental motion and generating predictions from it;
locating earthquakes; and radioisotope dating of rocks.
In the first activity, I gave students cutouts of the continents.
(The best way to find these is by googling terms related to this
activity; you can't just print a world map because of the distortion
inherent in most projections.) The cutouts were on their desks as the
students filed in, so it was interesting to see what the students did
without any instructions: mostly arrange them as they are now rather
than try to put them together like a puzzle. But it only took a small
hint to get them assembling the puzzle. Once each group settled on a
way of fitting the continents together, I had them glue the model to
one side of a handout I had prepared. On the other side they were
instructed to make four specific predictions about what would be
observable if this model were true. I had to drop some major hints,
but the groups did eventually come up with the same four major
categories: (1) fossils on once-adjacent pieces of land should be the
same even though they are now very far apart; (2) living creatures on
once-adjacent pieces of land should be similar (making allowance for
evolutionary changes and for especially mobile animals such as birds
to be excluded from this analysis; (3) an expanding ocean floor should
be young in the middle where it spreads apart, and progressively older
near the continents (some groups put more emphasis on finding an
identifiable mid-ocean feature, but it's basically the same idea); (4)
once-adjacent pieces of land should have very similar older rock
layers even though they are now very far apart. One thing no one got
even though I mentioned GPS is that we should be able to measure the
distance between, say, North America and Europe increasing very
slightly each year (it is, by a few centimeters per year).
I had planned for this to be iterative. In my original plan the
groups were to make a very specific prediction such as "fossils found
in this part of Antarctica match the fossils in this part of
Australia", and then I would look that up quickly (to prevent
computers from being a distraction), and then after seeing how all
four predictions went they would make a better model on a new sheet of
paper (I brought lots of continent cutouts). But the initial puzzle
assembling took much, much longer than I anticipated. Some groups
took a lot of time to trim their rough-cut continent cutouts in
exquisite detail; others rearranged theirs many times; others just
didn't focus as much as I would have liked. So we didn't go through
another iteration. But one lesson that was clear to me at least is
that although South America fits nicely into Africa, almost nothing
else matches that clearly. At some point you have to guess (this is
clear when comparing the different guesses of the different groups),
and at that point you have to look for fossil evidence to verify or
falsify your guess. That whole process is what science is really all
about!
In the time left before break, I asked the students to guess why the
continents move. They had a lot of crazy theories, but I steered it
back to what we had learned last week: the core of the Earth is hot,
heat flows to areas of lower temperature, and it can flow through
radiation, conduction, and/or convection. We talked about how each of
these might or might not apply in this case, and figured out that
convection is well suited to transporting heat through the mantle,
which is fluid although not really molten. Once we got this all into
a diagram with convection loops in the mantle, it was clear that this
was a very plausible mechanism for making continents move.
This whole activity took 45 minutes, and as I mentioned I probably
should have budgeted much longer, and/or come up with ways to save
lots of time on the puzzle-assembly. Devoting time to verify or
falsify specific predictions and come up with a better model would
have been a great illustration of the process of science. Maybe it
should be a homework. But, apart from this reservation, I think it's
a great activity.
model of continental motion and generating predictions from it;
locating earthquakes; and radioisotope dating of rocks.
In the first activity, I gave students cutouts of the continents.
(The best way to find these is by googling terms related to this
activity; you can't just print a world map because of the distortion
inherent in most projections.) The cutouts were on their desks as the
students filed in, so it was interesting to see what the students did
without any instructions: mostly arrange them as they are now rather
than try to put them together like a puzzle. But it only took a small
hint to get them assembling the puzzle. Once each group settled on a
way of fitting the continents together, I had them glue the model to
one side of a handout I had prepared. On the other side they were
instructed to make four specific predictions about what would be
observable if this model were true. I had to drop some major hints,
but the groups did eventually come up with the same four major
categories: (1) fossils on once-adjacent pieces of land should be the
same even though they are now very far apart; (2) living creatures on
once-adjacent pieces of land should be similar (making allowance for
evolutionary changes and for especially mobile animals such as birds
to be excluded from this analysis; (3) an expanding ocean floor should
be young in the middle where it spreads apart, and progressively older
near the continents (some groups put more emphasis on finding an
identifiable mid-ocean feature, but it's basically the same idea); (4)
once-adjacent pieces of land should have very similar older rock
layers even though they are now very far apart. One thing no one got
even though I mentioned GPS is that we should be able to measure the
distance between, say, North America and Europe increasing very
slightly each year (it is, by a few centimeters per year).
I had planned for this to be iterative. In my original plan the
groups were to make a very specific prediction such as "fossils found
in this part of Antarctica match the fossils in this part of
Australia", and then I would look that up quickly (to prevent
computers from being a distraction), and then after seeing how all
four predictions went they would make a better model on a new sheet of
paper (I brought lots of continent cutouts). But the initial puzzle
assembling took much, much longer than I anticipated. Some groups
took a lot of time to trim their rough-cut continent cutouts in
exquisite detail; others rearranged theirs many times; others just
didn't focus as much as I would have liked. So we didn't go through
another iteration. But one lesson that was clear to me at least is
that although South America fits nicely into Africa, almost nothing
else matches that clearly. At some point you have to guess (this is
clear when comparing the different guesses of the different groups),
and at that point you have to look for fossil evidence to verify or
falsify your guess. That whole process is what science is really all
about!
In the time left before break, I asked the students to guess why the
continents move. They had a lot of crazy theories, but I steered it
back to what we had learned last week: the core of the Earth is hot,
heat flows to areas of lower temperature, and it can flow through
radiation, conduction, and/or convection. We talked about how each of
these might or might not apply in this case, and figured out that
convection is well suited to transporting heat through the mantle,
which is fluid although not really molten. Once we got this all into
a diagram with convection loops in the mantle, it was clear that this
was a very plausible mechanism for making continents move.
This whole activity took 45 minutes, and as I mentioned I probably
should have budgeted much longer, and/or come up with ways to save
lots of time on the puzzle-assembly. Devoting time to verify or
falsify specific predictions and come up with a better model would
have been a great illustration of the process of science. Maybe it
should be a homework. But, apart from this reservation, I think it's
a great activity.
Saturday, December 15, 2012
Origins Part II
(This is a continuation of a previous post.)
After a short break, we tackled the Big Bang. I asked if we needed to
extend the timeline even further back than the origin of the Earth.
They were clear on the need to do so, since the Earth and the solar
system formed from a pre-existing cloud of gas. I showed them some
pictures of galaxies and then some of a fly-through movie of galaxies from
the Sloan Digital Sky Survey. I just wanted to roughly establish that
galaxies are like neighborhoods: we have ours, and we can see where
some others are too. It was clear later that they have no real idea
that galaxies are much bigger than the solar system (even though I
said it); they kept mixing up planets and galaxies. But I didn't
dwell on that; I figure there's only so much I can do in one morning,
and it was more important to establish that "things are moving apart"
than to work on a sense of scale.
Next, I took a long loose spring (almost like the helical telephone
cord that used to be on all landline phones) to which I had attached
galaxies (each galaxy had the name of a kid). Starting with the
spring scrunched up, I extended the spring 12 feet or so and got the
galaxies far apart. I did this a few times so they could see how all
galaxies moved away from each other. This was actually the first time
I had done this demo, and now I'm sure I will do it with my college
kids. I always use a balloon, and I still will, but there's something
nice about also doing the one-dimensional case. It just makes
everything a lot more visible, especially in a big room. With the
spring stretched I asked how we could figure out how long it has been
since everything was together. One kid figured it out right away. He
explained that knowing how fast they are moving and how far apart they
are, we can calculate the time it took. He used the example of a
speed of one inch per year. In that case, the number of inches apart
is the number of years it took to get that far apart. This was an
amazingly good answer; it was almost as if I had rehearsed it with him
beforehand and planted him in the audience (I swear I didn't).
Next we went outside and practiced doing the same thing with our
bodies. With Teacher Pa as the Milky Way, we all ran away from her.
Teacher Ethan ran the fastest and became the most distant galaxy by
the time I said stop. I wanted to make clear that the most distant
galaxy is further away not because it has been traveling for a longer
time, and that there was a time when all galaxies were together. We
went back inside and I drew a diagram of us as someone above the field
would have seen us. If that person came upon that scene and saw us
moving very slowly, would he guess that we had started a long time
ago, or a short time ago? (Long.) If that person came upon that
scene and saw us moving very quickly, would he guess that we had
started a long time ago, or a short time ago? (Short.) Using the same
logic, astronomers have found that all galaxies were together and
started moving apart (the Big Bang) 13.7 billion years ago. I made a
big show of extending the timeline into the hallway and out of the
school to emphasize that that is a long time.
Now, the kids may have gotten the wrong impression that we are at the
center because everything is expanding away from us. To combat that,
I had prepared two transparencies. One has a smattering of galaxies, each
with a different shape so that it's recognizable. I had prepared this by putting
graph paper behind the transparency and drawing galaxies at random coordinates.
I prepared the second one by drawing the same galaxies (now in red instead
of black) at the same coordinates multiplied by 1.5. You can pick one galaxy
in the middle to represent the Milky Way and show the initial (black) transparency
to show where the other galaxies are around it. Then overlay the red one, matching
up the Milky Way's position, to see how everything moved away from us. Here's the
cool part: now you pretend you are an alien in another galaxy, match up that galaxy
across the two transparencies, and you ALSO see that everything is expanding away
from the alien! This blew everyone's mind, including the teachers. We spent a fair
amount of time with the kids picking a galaxy, and me matching that galaxy and
showing that everything moved away from it. Bottom line: just because we
observe everything moving away from us doesn't mean we're at the center. When
there's more space everywhere, EVERY galaxy can observe this. We're not special.
People often ask, where did the Big Bang happen? It happened everywhere,
including here! All the places that all the aliens in the universe could call "here"
all overlapped , in the distant past, with what WE call "here"! I reinforced this with
the traditional balloon demo of the expanding universe: draw some dots on a partially inflated balloon, then fully inflate it and show how each dot is further from each other dot, but none is in a special or central position. If the balloon could really be completely collapsed, then all the dots would be in the same starting position without ever really moving away from its position on the balloon.
But, should we believe that we can extrapolate that far back in time?
We should look for evidence! I made a lame show of demonstrating how
things are hot when compressed (I brandished a bike pump and asked
them to notice how the valve gets hot next time they pump up a tire),
so that the whole universe would have been red hot at some point in
the past when it was highly compressed. We actually see that light:
it's called the cosmic microwave background. This is fossil evidence
of a hot early universe.
We were running out of time but the kids voted to do the marshmallow
activity rather than just stop early. I had brought white and yellow
mini marshmallows and toothpicks. These represent the building blocks
of atoms (technically, protons and neutrons, but I didn't use those
words). These building blocks can be stuck together only at very,
very high temperatures which the universe experienced only in the
first three minutes, when it was even hotter than red hot. (Kind of
like marshmallows will stick together if heated.) We had talked about
solids, liquids, and gases in previous weeks, so I sketched out
hydrogen (just one proton) and helium (two protons and two neutrons),
which they knew were gases. I had set up cups half full of a mix of
protons and neutrons, in a 7:1 ratio. I gave them the cups and told
them they had only three minutes to build as much helium (ie stick two
white and two yellows on a toothpick) as they could. Because of the
paucity of neutrons, they were typically able to build only 3 helium
atoms, with about 36 hydrogen atoms left over. This is actually the
ratio we observe! So the atoms themselves are additional fossil
evidence of a very hot early universe. [Parents: if you're curious
where the 7:1 ratio came from, that came from the even hotter
conditions in the first fraction of a second, and the observed ratio
agrees with the Big Bang model, thus providing even further fossil
evidence. If you want to read more, search "Big Bang nucleosynthesis."]
Overall, it was a VERY successful day. The kids had many additional
questions about planets and orbits which I didn't take time to answer,
and this could form the basis of an activity for my next visit, and I
do think they gained an appreciation of the basic idea that we can
tell the age of the universe from how fast it's expanding. How well
they'll remember that or be able to answer questions on an assessment,
I'm not confident. But the basic idea is not beyond the grasp of 1st
and second graders. The movie we saw before the break was great, the
spring demo was great, and the marshmallow activity was good. (We
didn't have enough time to do it really well, but it's a very
promising idea and I will develop it further. Given more time, I
would have the kids make mini posters with "raw ingredients" "elements
after cooking in the heat of the Big Bang.") The radioisotope dating with
dominoes (see previous post) came up a bit lame, but I think it's a good idea
that just needs more refinement.
As the kids went to lunch, I worked on the science section of Teacher
Pa's poster comparing different religions' creation stories. Because
I wanted to emphasize the LACK of parallelism as discussed in my
previous post, I ripped off the science column and posted it on the
wall next to the window where the religion part of the poster was. I
also did not carry over the formatting of the rows in the religion
column. I hope to post a picture here rather than describe it in
words, but I think I achieved the right balance in emphasizing how
science is different from religion while respecting both.
Update: if you look at this picture full size, you will be able to read the poster.
After a short break, we tackled the Big Bang. I asked if we needed to
extend the timeline even further back than the origin of the Earth.
They were clear on the need to do so, since the Earth and the solar
system formed from a pre-existing cloud of gas. I showed them some
pictures of galaxies and then some of a fly-through movie of galaxies from
the Sloan Digital Sky Survey. I just wanted to roughly establish that
galaxies are like neighborhoods: we have ours, and we can see where
some others are too. It was clear later that they have no real idea
that galaxies are much bigger than the solar system (even though I
said it); they kept mixing up planets and galaxies. But I didn't
dwell on that; I figure there's only so much I can do in one morning,
and it was more important to establish that "things are moving apart"
than to work on a sense of scale.
Next, I took a long loose spring (almost like the helical telephone
cord that used to be on all landline phones) to which I had attached
galaxies (each galaxy had the name of a kid). Starting with the
spring scrunched up, I extended the spring 12 feet or so and got the
galaxies far apart. I did this a few times so they could see how all
galaxies moved away from each other. This was actually the first time
I had done this demo, and now I'm sure I will do it with my college
kids. I always use a balloon, and I still will, but there's something
nice about also doing the one-dimensional case. It just makes
everything a lot more visible, especially in a big room. With the
spring stretched I asked how we could figure out how long it has been
since everything was together. One kid figured it out right away. He
explained that knowing how fast they are moving and how far apart they
are, we can calculate the time it took. He used the example of a
speed of one inch per year. In that case, the number of inches apart
is the number of years it took to get that far apart. This was an
amazingly good answer; it was almost as if I had rehearsed it with him
beforehand and planted him in the audience (I swear I didn't).
Next we went outside and practiced doing the same thing with our
bodies. With Teacher Pa as the Milky Way, we all ran away from her.
Teacher Ethan ran the fastest and became the most distant galaxy by
the time I said stop. I wanted to make clear that the most distant
galaxy is further away not because it has been traveling for a longer
time, and that there was a time when all galaxies were together. We
went back inside and I drew a diagram of us as someone above the field
would have seen us. If that person came upon that scene and saw us
moving very slowly, would he guess that we had started a long time
ago, or a short time ago? (Long.) If that person came upon that
scene and saw us moving very quickly, would he guess that we had
started a long time ago, or a short time ago? (Short.) Using the same
logic, astronomers have found that all galaxies were together and
started moving apart (the Big Bang) 13.7 billion years ago. I made a
big show of extending the timeline into the hallway and out of the
school to emphasize that that is a long time.
Now, the kids may have gotten the wrong impression that we are at the
center because everything is expanding away from us. To combat that,
I had prepared two transparencies. One has a smattering of galaxies, each
with a different shape so that it's recognizable. I had prepared this by putting
graph paper behind the transparency and drawing galaxies at random coordinates.
I prepared the second one by drawing the same galaxies (now in red instead
of black) at the same coordinates multiplied by 1.5. You can pick one galaxy
in the middle to represent the Milky Way and show the initial (black) transparency
to show where the other galaxies are around it. Then overlay the red one, matching
up the Milky Way's position, to see how everything moved away from us. Here's the
cool part: now you pretend you are an alien in another galaxy, match up that galaxy
across the two transparencies, and you ALSO see that everything is expanding away
from the alien! This blew everyone's mind, including the teachers. We spent a fair
amount of time with the kids picking a galaxy, and me matching that galaxy and
showing that everything moved away from it. Bottom line: just because we
observe everything moving away from us doesn't mean we're at the center. When
there's more space everywhere, EVERY galaxy can observe this. We're not special.
People often ask, where did the Big Bang happen? It happened everywhere,
including here! All the places that all the aliens in the universe could call "here"
all overlapped , in the distant past, with what WE call "here"! I reinforced this with
the traditional balloon demo of the expanding universe: draw some dots on a partially inflated balloon, then fully inflate it and show how each dot is further from each other dot, but none is in a special or central position. If the balloon could really be completely collapsed, then all the dots would be in the same starting position without ever really moving away from its position on the balloon.
But, should we believe that we can extrapolate that far back in time?
We should look for evidence! I made a lame show of demonstrating how
things are hot when compressed (I brandished a bike pump and asked
them to notice how the valve gets hot next time they pump up a tire),
so that the whole universe would have been red hot at some point in
the past when it was highly compressed. We actually see that light:
it's called the cosmic microwave background. This is fossil evidence
of a hot early universe.
We were running out of time but the kids voted to do the marshmallow
activity rather than just stop early. I had brought white and yellow
mini marshmallows and toothpicks. These represent the building blocks
of atoms (technically, protons and neutrons, but I didn't use those
words). These building blocks can be stuck together only at very,
very high temperatures which the universe experienced only in the
first three minutes, when it was even hotter than red hot. (Kind of
like marshmallows will stick together if heated.) We had talked about
solids, liquids, and gases in previous weeks, so I sketched out
hydrogen (just one proton) and helium (two protons and two neutrons),
which they knew were gases. I had set up cups half full of a mix of
protons and neutrons, in a 7:1 ratio. I gave them the cups and told
them they had only three minutes to build as much helium (ie stick two
white and two yellows on a toothpick) as they could. Because of the
paucity of neutrons, they were typically able to build only 3 helium
atoms, with about 36 hydrogen atoms left over. This is actually the
ratio we observe! So the atoms themselves are additional fossil
evidence of a very hot early universe. [Parents: if you're curious
where the 7:1 ratio came from, that came from the even hotter
conditions in the first fraction of a second, and the observed ratio
agrees with the Big Bang model, thus providing even further fossil
evidence. If you want to read more, search "Big Bang nucleosynthesis."]
Overall, it was a VERY successful day. The kids had many additional
questions about planets and orbits which I didn't take time to answer,
and this could form the basis of an activity for my next visit, and I
do think they gained an appreciation of the basic idea that we can
tell the age of the universe from how fast it's expanding. How well
they'll remember that or be able to answer questions on an assessment,
I'm not confident. But the basic idea is not beyond the grasp of 1st
and second graders. The movie we saw before the break was great, the
spring demo was great, and the marshmallow activity was good. (We
didn't have enough time to do it really well, but it's a very
promising idea and I will develop it further. Given more time, I
would have the kids make mini posters with "raw ingredients" "elements
after cooking in the heat of the Big Bang.") The radioisotope dating with
dominoes (see previous post) came up a bit lame, but I think it's a good idea
that just needs more refinement.
As the kids went to lunch, I worked on the science section of Teacher
Pa's poster comparing different religions' creation stories. Because
I wanted to emphasize the LACK of parallelism as discussed in my
previous post, I ripped off the science column and posted it on the
wall next to the window where the religion part of the poster was. I
also did not carry over the formatting of the rows in the religion
column. I hope to post a picture here rather than describe it in
words, but I think I achieved the right balance in emphasizing how
science is different from religion while respecting both.
Update: if you look at this picture full size, you will be able to read the poster.
Friday, December 14, 2012
Origins Part I
Teacher Pa's class as been studying various religions, including their
creation stories, this week, so she asked me to review the scientific
"creation story" with the kids. She had made a big poster with
Hinduism, Judaism, Christianity, and Islam as column headings, each
with entries in rows titled [Name of] God, [Sacred] Book, Creation
Story, Golden Rule, What Happens After Death, and Holidays, and she
wanted me to fill in a Science column for Creation Story, Golden Rule,
and What Happens After Death.
I wanted to make very, VERY clear to the kids that science is not
another religion, so I refused to tell a "creation story" and instead
made a detective story about our origins. (It turns out I was
justified: even after spending the whole morning with the kids and
emphasizing how science works, as the kids went to lunch I began
ripping the Science column off the religion poster and my own son
Linus said, "Dad, what holidays does science celebrate?")
I started the morning by discussing what kinds of questions science
can answer and what kinds of questions it can't. If you're about to
bite into your last cookie and someone asks you to share it, can
science help you figure out if you should share it? No. If your best
friend moves away and you're lonely, can science help you figure out
what to do? No. Religion might help you with those questions. But
if you have a question about nature, such as "When did the Earth
begin?", then science can help. I think it's super-important to help
kids draw these distinctions. Because religion tries to say something
about our origins, and so does science, it's tempting to make
parallels between them. But the differences are more important then
the superficial parallels, and we need to help kids see that. Science
and religion are simply about different things. If we had a poster
comparing different sports, we wouldn't put Sudoku on it!
The kids had done a timeline of the history of Davis, so I started
with a blank timeline with "Now" on the right and "?" on the left. I
put a few recent events (the years they were born) close to "Now" and
asked how we could know about the distant past using evidence (clues).
Because they had recently been to Yosemite and seen a slice of a tree
with about 1,000 rings, I started with that: we know that trees grow
one ring each year, so this tree tells us that Earth is at least 1,000
years old. In fact, the oldest trees in the world live in California
and they are over 4,000 years old, so I marked that too. (Aside: by
matching long-dead trees with just-felled trees [using ring thickness
as an indicator of how good for growth each year was], scientists have
been able to put together tree-ring histories going back about 10,000
years!)
Next, we moved on to rocks. They had studied some geology in
preparation for Yosemite, so we reviewed how long it takes millions of
years for a river to carve a canyon, based on how fast we observe it
carving today. So Earth is at least millions of years old. One kid
knew that some rocks are at least 1,000,000,000 (one billion...I wrote
out the number to impress them) years old. But how, I asked.
"Dating." OK, but how do we do that? I did a very simplified version
of radioisotope dating. I took some dominoes and stood them up on a
desk. Standing up, they have some potential energy, because they have
the potential to fall. Once fallen, they don't have potential energy.
(We had talked a bit about this concept previously.) Now some atoms
in your bones (or in rocks) have this extra potential energy, but as
time goes on more and more of them lose this. I knocked down a few to
illustrate the passage of some time, then a few more to illustrate the
passage of more time, etc. They quickly got the idea of "more down
equals older" (I gave them many scenarios and they got the relative
ages right) but I'm not sure what they were really visualizing when we
said "more energy" or "fall down" because I got questions about
whether the atoms are dead or had changed into something else. A nice
thing about these dominoes was that they came in different colors, so
it was easy to point out that this domino is still a red domino with 5
and 2 dots, it's just that it doesn't have extra energy now. So I
think the got the idea that we were using small particles in the rocks
as a clock, but not much else. Which is probably ok; you can't do
everything. (If I had planned this whole semester better I probably
would have brought in a microscope very early on, and established the
concept of atoms so that I could safely refer to it throughout the
semester...last year all the kids in the school studied atoms but only
one of those kids is in this room this year.)
So I extended the timeline all the way across the other (very long)
whiteboard and wrote 4,500,000,000 as the age of the oldest rocks on
Earth. I then mentioned meteors, which they had heard of, and how
their slamming together would generate heat. (I slammed clay lumps
together for visual effect.) We think Earth was formed by meteors
slamming together and creating so much heat that they melted together.
The rock-dating clock starts when the rock solidifies, so the age of
the Earth is 4,500,000,000 years. I then wanted to show them a movie
rendering of this process, and I showed the first few minutes of the
Birth of the Earth episode of How the Earth Was Made; in the first
several minutes they have some really nice visualizations of this.
But they like it so much that we kept watching, well into break time,
and almost finished. But with about 10 minutes left in the 43-minute
episode, I really wanted them to stretch their legs so we encourage
them to go outside but left the option of continuing to watch. Half
the kids watched to the end. I highly recommend this episode, and in
fact this whole series. It emphasizes the use of evidence to test
ideas.
The kids had MANY questions in response to the video. It was great to click Pause as soon as a question arose so I could deal with it right away. I felt like the movie was an awesome way to keep their attention (which is sometimes a struggle), but I could still provide an interactive teaching environment. It was the best of both worlds.
I have a lot more to say about what we did after break, but I'll make
that another post. To be continued....
creation stories, this week, so she asked me to review the scientific
"creation story" with the kids. She had made a big poster with
Hinduism, Judaism, Christianity, and Islam as column headings, each
with entries in rows titled [Name of] God, [Sacred] Book, Creation
Story, Golden Rule, What Happens After Death, and Holidays, and she
wanted me to fill in a Science column for Creation Story, Golden Rule,
and What Happens After Death.
I wanted to make very, VERY clear to the kids that science is not
another religion, so I refused to tell a "creation story" and instead
made a detective story about our origins. (It turns out I was
justified: even after spending the whole morning with the kids and
emphasizing how science works, as the kids went to lunch I began
ripping the Science column off the religion poster and my own son
Linus said, "Dad, what holidays does science celebrate?")
I started the morning by discussing what kinds of questions science
can answer and what kinds of questions it can't. If you're about to
bite into your last cookie and someone asks you to share it, can
science help you figure out if you should share it? No. If your best
friend moves away and you're lonely, can science help you figure out
what to do? No. Religion might help you with those questions. But
if you have a question about nature, such as "When did the Earth
begin?", then science can help. I think it's super-important to help
kids draw these distinctions. Because religion tries to say something
about our origins, and so does science, it's tempting to make
parallels between them. But the differences are more important then
the superficial parallels, and we need to help kids see that. Science
and religion are simply about different things. If we had a poster
comparing different sports, we wouldn't put Sudoku on it!
The kids had done a timeline of the history of Davis, so I started
with a blank timeline with "Now" on the right and "?" on the left. I
put a few recent events (the years they were born) close to "Now" and
asked how we could know about the distant past using evidence (clues).
Because they had recently been to Yosemite and seen a slice of a tree
with about 1,000 rings, I started with that: we know that trees grow
one ring each year, so this tree tells us that Earth is at least 1,000
years old. In fact, the oldest trees in the world live in California
and they are over 4,000 years old, so I marked that too. (Aside: by
matching long-dead trees with just-felled trees [using ring thickness
as an indicator of how good for growth each year was], scientists have
been able to put together tree-ring histories going back about 10,000
years!)
Next, we moved on to rocks. They had studied some geology in
preparation for Yosemite, so we reviewed how long it takes millions of
years for a river to carve a canyon, based on how fast we observe it
carving today. So Earth is at least millions of years old. One kid
knew that some rocks are at least 1,000,000,000 (one billion...I wrote
out the number to impress them) years old. But how, I asked.
"Dating." OK, but how do we do that? I did a very simplified version
of radioisotope dating. I took some dominoes and stood them up on a
desk. Standing up, they have some potential energy, because they have
the potential to fall. Once fallen, they don't have potential energy.
(We had talked a bit about this concept previously.) Now some atoms
in your bones (or in rocks) have this extra potential energy, but as
time goes on more and more of them lose this. I knocked down a few to
illustrate the passage of some time, then a few more to illustrate the
passage of more time, etc. They quickly got the idea of "more down
equals older" (I gave them many scenarios and they got the relative
ages right) but I'm not sure what they were really visualizing when we
said "more energy" or "fall down" because I got questions about
whether the atoms are dead or had changed into something else. A nice
thing about these dominoes was that they came in different colors, so
it was easy to point out that this domino is still a red domino with 5
and 2 dots, it's just that it doesn't have extra energy now. So I
think the got the idea that we were using small particles in the rocks
as a clock, but not much else. Which is probably ok; you can't do
everything. (If I had planned this whole semester better I probably
would have brought in a microscope very early on, and established the
concept of atoms so that I could safely refer to it throughout the
semester...last year all the kids in the school studied atoms but only
one of those kids is in this room this year.)
So I extended the timeline all the way across the other (very long)
whiteboard and wrote 4,500,000,000 as the age of the oldest rocks on
Earth. I then mentioned meteors, which they had heard of, and how
their slamming together would generate heat. (I slammed clay lumps
together for visual effect.) We think Earth was formed by meteors
slamming together and creating so much heat that they melted together.
The rock-dating clock starts when the rock solidifies, so the age of
the Earth is 4,500,000,000 years. I then wanted to show them a movie
rendering of this process, and I showed the first few minutes of the
Birth of the Earth episode of How the Earth Was Made; in the first
several minutes they have some really nice visualizations of this.
But they like it so much that we kept watching, well into break time,
and almost finished. But with about 10 minutes left in the 43-minute
episode, I really wanted them to stretch their legs so we encourage
them to go outside but left the option of continuing to watch. Half
the kids watched to the end. I highly recommend this episode, and in
fact this whole series. It emphasizes the use of evidence to test
ideas.
The kids had MANY questions in response to the video. It was great to click Pause as soon as a question arose so I could deal with it right away. I felt like the movie was an awesome way to keep their attention (which is sometimes a struggle), but I could still provide an interactive teaching environment. It was the best of both worlds.
I have a lot more to say about what we did after break, but I'll make
that another post. To be continued....
Friday, September 14, 2012
Mystery tubes 2012
This year I have a new title (scientist in residence) at Peregrine School, and a new format: every Friday morning with grades 1-2 for three months, then with grades 5-7 for three months, then grades 3-4 for three months. This should allow me to go much further in depth with each group, and to facilitate really substantive projects on their part. Today was my first day with the five first and second graders, and to break the ice I brought some "mystery tubes" which are basically like the one shown on this short video.
The students got their hands on the tubes, did any experiment they wanted to (short of looking inside the tubes), and drew what they thought was inside. Most students went through a couple of iterations as they realized that their first model wouldn't reproduce their observations. When a student was satisfied with his/her drawing, I brought out toilet paper tubes, strings, beads, etc so they could build a model and show that it behaved like the real thing. The point: science is about building models (usually mental models rather than physical models), and this activity allows us to practice many aspects of this in one session, including thinking of experiments to test the model, performing those experiments, generating predictions from the model (hypothetico-deductive reasoning), and comparing the results of the experiments to predictions generated from the model. Furthermore, since I never allowed them to look inside the tube we had ample opportunity to discuss how science is less about knowing the right answer than about the process of finding answers. After all, nature never tells us the right answer directly. Kids at this age are very much in the mode of gaining knowledge from books, but it is worth making them stop and think about how every bit of the knowledge in books was, at some point, figured out by someone who had to figure out by reasoning and then convince other people that it was correct.
You can also read about the way I did this activity with mixed ages (grades 1-6) last year. A note for teachers using this activity: it took much more time this year, 45 minutes, because the 1-2 graders did not have the fine motor skills to easily build their little toilet-paper-tube model with strings and beads. With mixed ages last year, it seemed as if the young ones contributed equally intellectually, but the older ones probably did the actual tying of strings and beads. And the 45 minutes was with two adults helping four kids! If you try it with a larger group of 1-2 graders, you'll have to bring full-size materials. I do this activity with college students (who find it interesting and beneficial) so this activity is remarkable for the range of ages who find it suitable!
I learned something from Teacher Marcia too. With five minutes remaining in the period, I wanted to have a wrap-up discussion with the kids. She showed me a way to make kids pay full attention to the wrap-up discussion rather than surreptitiously keep working on their model: move them from the material-strewn desks over to the rug where they listen to stories etc. This was brilliant. Now if I can figure out how to do this with college students, I'll be set!
The students got their hands on the tubes, did any experiment they wanted to (short of looking inside the tubes), and drew what they thought was inside. Most students went through a couple of iterations as they realized that their first model wouldn't reproduce their observations. When a student was satisfied with his/her drawing, I brought out toilet paper tubes, strings, beads, etc so they could build a model and show that it behaved like the real thing. The point: science is about building models (usually mental models rather than physical models), and this activity allows us to practice many aspects of this in one session, including thinking of experiments to test the model, performing those experiments, generating predictions from the model (hypothetico-deductive reasoning), and comparing the results of the experiments to predictions generated from the model. Furthermore, since I never allowed them to look inside the tube we had ample opportunity to discuss how science is less about knowing the right answer than about the process of finding answers. After all, nature never tells us the right answer directly. Kids at this age are very much in the mode of gaining knowledge from books, but it is worth making them stop and think about how every bit of the knowledge in books was, at some point, figured out by someone who had to figure out by reasoning and then convince other people that it was correct.
You can also read about the way I did this activity with mixed ages (grades 1-6) last year. A note for teachers using this activity: it took much more time this year, 45 minutes, because the 1-2 graders did not have the fine motor skills to easily build their little toilet-paper-tube model with strings and beads. With mixed ages last year, it seemed as if the young ones contributed equally intellectually, but the older ones probably did the actual tying of strings and beads. And the 45 minutes was with two adults helping four kids! If you try it with a larger group of 1-2 graders, you'll have to bring full-size materials. I do this activity with college students (who find it interesting and beneficial) so this activity is remarkable for the range of ages who find it suitable!
I learned something from Teacher Marcia too. With five minutes remaining in the period, I wanted to have a wrap-up discussion with the kids. She showed me a way to make kids pay full attention to the wrap-up discussion rather than surreptitiously keep working on their model: move them from the material-strewn desks over to the rug where they listen to stories etc. This was brilliant. Now if I can figure out how to do this with college students, I'll be set!
Monday, April 9, 2012
Dinosaur layer cake
Some of the boys in Primaria are really into dinosaurs and have been
asking for a dinosaur-related experiment. By talking to them on
previous visits, I got a sense of what would be useful. They knew
that dinosaurs did not live at the same time as cavemen, but they
didn't know how we know that. Understanding this brings together a
lot of key ideas in geology and in scientific reasoning, so I thought
it would make a great activity. But it turned out to be more of a
demo than a small-group activity, so it fit the schedule well on a day
when there was less time for science due to the Easter egg hunt.
I brought a large, clear plastic box and set it on a table in the
outdoor area. As part of the setup I also filled some buckets with
different materials in the yard: sand, wood chips, and black dirt from
the planter boxes. I started, as usual, by asking them what they know
about the topic, and I tried to steer the resulting conversation
toward how they know what they know. (Aside: this is one of the few
times I had a conversation with the entire class of 20+ kids at once,
and it was surprisingly not chaotic. It really helped to have them
seated before the start, with everyone able to see because I was on a
platform.) One boy was able to give an answer like "men hadn't
evolved yet" but no one know how we know that. So that provided the
motivation for the following demo.
As part of the preparation, I had also printed out skeletons of
different dinosaurs as well as Lucy and a modern human, and glued
these to pieces of cardboard. I pulled out the stegosaurus and asked,
"Who knows what this is?" Then we imagined stegosaurus caught in a
mudslide. I had a volunteer help me pour the bucket of sand over the
stegosaurus (in the large clear plastic box). Then, some time later,
here comes a...does anyone know what this is? Triceratops.
Triceratops dies and gets buried in a layer of wood chips, symbolizing
a different type of soil in that area at that time, which ultimately
forms a different layer of rock. We repeated with a T. Rex and
another layer of sand.
Then we imagined that the area was underwater for a time. We talked
about how an area could be underwater at times and above water at
other times. We reviewed what they had learned about rivers and the
water cycle, and decided that layers of sediment can build up on the
lake's bottom or the sea floor. We also related it to what they had
learned about the deep ocean, that things (like whale bones and
smaller bits of nutrients) rain down from above. We simulated this by
having a few volunteers rain down black dirt, while I dropped an
elasmosaurus skeleton in.
Next, I did a special, thin, brightly colored layer using a bottle of
paprika. They guessed it represented lava but I said we would come
back to discuss it later.
Then I brought out Lucy and discussed her, buried her in another layer
of wood chips and then brought out the modern human skeleton and
buried him in a final layer of sand. The final product was
impressive, clearly showing seven different layers of "rock" through
the clear plastic. (The box was about 2.5 feet long by 1.5 wide by
1.5 feet deep, and was about 2/3 filled by the end.) We discussed how
the oldest rock layers are on the bottom and the newest are on the
top, so that the fossils we find on the bottom layers are of creatures
who lived long ago, and the fossils we find on the top layers are of
creatures who lived recently. (This is true even if an earthquake
comes later and tilts the layers. I tilted the box and asked who had
been to the Grand Canyon and seen the tilted layers there; a
substantial minority had seen it.) Do we ever find cavemen (Lucy) on
the bottom layers? No. Do we ever find dinosaurs on the top layers?
No. We can even tell which dinosaurs lived earlier, and which lived
later.
Next, I had them exercise their hypothetico-deductive reasoning
skills. If Lucy had lived as early as the dinosaurs, what would we
find? If the dinosaurs had lived as late as Lucy, what would we find?
Finally, I returned to the thin paprika band. All over the world, we
find an easily identifiable band called the K-T boundary, and we find
dinosaur fossils only below that band, indicating that dinosaurs died
out around the time the band was formed. And the band has been found
to contain an element, iridium, in much higher concentrations than
normally found on Earth, but consistent with a certain type of
asteroid. The conclusion is that an asteroid impact and its aftermath
killed the dinosaurs.
I'm aware that this model is not universally accepted; some scientists
think volcanism played a role in the demise of the dinosaurs, and some
think the dinosaurs were dying out before the asteroid impact, which
perhaps only delivered the coup de grace. But there's only so much
detail you can go into with five-year-olds. The best thing I can do
to help them deal with nuance as they grow more sophisticated is to
give them practice reasoning with evidence, just as I did.
I left the whole layer cake for the kids to excavate in their free time after lunch.
I had originally envisioned doing something which would make the layers set more
like stone so they would really have to chip away at it, but after finding out that
plaster of paris is toxic, decided not to go there. I suppose a weak concrete might work,
and I may return to this idea in future years. If I had done plaster or concrete, I would
have found something to color the layers slightly so they would show a bit of contrast.
As it happened, the sand/woodchips/black dirt made a beautiful set of layers.
I highly recommend reading this story of how Walter Alvarez and collaborators figured out the K-T boundary. It really shows how
science works; it involves far more creativity and discovery than most
students are led to believe by being forced to do contrived lab
exercises in school. Unfortunately, many K12 teachers have
experienced science only in that contrived, uninteresting context, and
themselves do not believe science requires creativity, and therefore
create a vicious cycle when they pass that attitude on to their
students. I'll sign off with this link to a list of misconceptions about science.
asking for a dinosaur-related experiment. By talking to them on
previous visits, I got a sense of what would be useful. They knew
that dinosaurs did not live at the same time as cavemen, but they
didn't know how we know that. Understanding this brings together a
lot of key ideas in geology and in scientific reasoning, so I thought
it would make a great activity. But it turned out to be more of a
demo than a small-group activity, so it fit the schedule well on a day
when there was less time for science due to the Easter egg hunt.
I brought a large, clear plastic box and set it on a table in the
outdoor area. As part of the setup I also filled some buckets with
different materials in the yard: sand, wood chips, and black dirt from
the planter boxes. I started, as usual, by asking them what they know
about the topic, and I tried to steer the resulting conversation
toward how they know what they know. (Aside: this is one of the few
times I had a conversation with the entire class of 20+ kids at once,
and it was surprisingly not chaotic. It really helped to have them
seated before the start, with everyone able to see because I was on a
platform.) One boy was able to give an answer like "men hadn't
evolved yet" but no one know how we know that. So that provided the
motivation for the following demo.
As part of the preparation, I had also printed out skeletons of
different dinosaurs as well as Lucy and a modern human, and glued
these to pieces of cardboard. I pulled out the stegosaurus and asked,
"Who knows what this is?" Then we imagined stegosaurus caught in a
mudslide. I had a volunteer help me pour the bucket of sand over the
stegosaurus (in the large clear plastic box). Then, some time later,
here comes a...does anyone know what this is? Triceratops.
Triceratops dies and gets buried in a layer of wood chips, symbolizing
a different type of soil in that area at that time, which ultimately
forms a different layer of rock. We repeated with a T. Rex and
another layer of sand.
Then we imagined that the area was underwater for a time. We talked
about how an area could be underwater at times and above water at
other times. We reviewed what they had learned about rivers and the
water cycle, and decided that layers of sediment can build up on the
lake's bottom or the sea floor. We also related it to what they had
learned about the deep ocean, that things (like whale bones and
smaller bits of nutrients) rain down from above. We simulated this by
having a few volunteers rain down black dirt, while I dropped an
elasmosaurus skeleton in.
Next, I did a special, thin, brightly colored layer using a bottle of
paprika. They guessed it represented lava but I said we would come
back to discuss it later.
Then I brought out Lucy and discussed her, buried her in another layer
of wood chips and then brought out the modern human skeleton and
buried him in a final layer of sand. The final product was
impressive, clearly showing seven different layers of "rock" through
the clear plastic. (The box was about 2.5 feet long by 1.5 wide by
1.5 feet deep, and was about 2/3 filled by the end.) We discussed how
the oldest rock layers are on the bottom and the newest are on the
top, so that the fossils we find on the bottom layers are of creatures
who lived long ago, and the fossils we find on the top layers are of
creatures who lived recently. (This is true even if an earthquake
comes later and tilts the layers. I tilted the box and asked who had
been to the Grand Canyon and seen the tilted layers there; a
substantial minority had seen it.) Do we ever find cavemen (Lucy) on
the bottom layers? No. Do we ever find dinosaurs on the top layers?
No. We can even tell which dinosaurs lived earlier, and which lived
later.
Next, I had them exercise their hypothetico-deductive reasoning
skills. If Lucy had lived as early as the dinosaurs, what would we
find? If the dinosaurs had lived as late as Lucy, what would we find?
Finally, I returned to the thin paprika band. All over the world, we
find an easily identifiable band called the K-T boundary, and we find
dinosaur fossils only below that band, indicating that dinosaurs died
out around the time the band was formed. And the band has been found
to contain an element, iridium, in much higher concentrations than
normally found on Earth, but consistent with a certain type of
asteroid. The conclusion is that an asteroid impact and its aftermath
killed the dinosaurs.
I'm aware that this model is not universally accepted; some scientists
think volcanism played a role in the demise of the dinosaurs, and some
think the dinosaurs were dying out before the asteroid impact, which
perhaps only delivered the coup de grace. But there's only so much
detail you can go into with five-year-olds. The best thing I can do
to help them deal with nuance as they grow more sophisticated is to
give them practice reasoning with evidence, just as I did.
I left the whole layer cake for the kids to excavate in their free time after lunch.
I had originally envisioned doing something which would make the layers set more
like stone so they would really have to chip away at it, but after finding out that
plaster of paris is toxic, decided not to go there. I suppose a weak concrete might work,
and I may return to this idea in future years. If I had done plaster or concrete, I would
have found something to color the layers slightly so they would show a bit of contrast.
As it happened, the sand/woodchips/black dirt made a beautiful set of layers.
I highly recommend reading this story of how Walter Alvarez and collaborators figured out the K-T boundary. It really shows how
science works; it involves far more creativity and discovery than most
students are led to believe by being forced to do contrived lab
exercises in school. Unfortunately, many K12 teachers have
experienced science only in that contrived, uninteresting context, and
themselves do not believe science requires creativity, and therefore
create a vicious cycle when they pass that attitude on to their
students. I'll sign off with this link to a list of misconceptions about science.
Saturday, March 10, 2012
Epistemology 101
A little side note on yesterday's class: I knew some students in the upper
grades had studied electricity before, but I decided to start at a
pretty basic level with static electricity, to make sure everyone
really understood what they thought they understood. At some point a
student volunteered an answer to one of my questions, and I asked,
"How do you know that?" with the intention of highlighting how the
student's conclusion followed from the things we had just observed.
But the student said she knew it because a teacher (in a previous
year) had told her, so I asked how the teacher knew that. The
response: that teacher had a teacher at some point. So where did THAT
teacher learn it? The whole class was eagerly getting in on the act
and shouting out different answers by this point, but one answer was
"From scientists." So how did scientists learn it? Eventually we came
back to the idea of doing experiments and learning from them.
I think this was really useful because too many people are stuck at
the first stage of epistemology: knowledge comes from an authority,
and that's that. Of course, it's normal at this age (grades 4-6), but
I'd like to do whatever I can do to move the kids on through the next
stages. It goes to the very nature of science: is it just a set of
results, or is it the process? It's both, of course, but the process
too often gets short shrift in education. It's difficult to
teach---it can't be a unit by itself, rather it has to be built in to
every science unit, which makes the logistics very difficult---and
it's difficult to write a test question about it. But it has to be
done.
If you're interested in what thoughtful people have discovered about
the stages of epistemology, you might start with this quick summary of William G. Perry's research.
The second group, grades 1-3, would have missed out on this except
that at some point I said, "Here's what I think is going on," and one
student said. "You're the teacher, you should KNOW what's going on" or
something like that. So that was a good chance to have a similar
discussion with that group.
grades had studied electricity before, but I decided to start at a
pretty basic level with static electricity, to make sure everyone
really understood what they thought they understood. At some point a
student volunteered an answer to one of my questions, and I asked,
"How do you know that?" with the intention of highlighting how the
student's conclusion followed from the things we had just observed.
But the student said she knew it because a teacher (in a previous
year) had told her, so I asked how the teacher knew that. The
response: that teacher had a teacher at some point. So where did THAT
teacher learn it? The whole class was eagerly getting in on the act
and shouting out different answers by this point, but one answer was
"From scientists." So how did scientists learn it? Eventually we came
back to the idea of doing experiments and learning from them.
I think this was really useful because too many people are stuck at
the first stage of epistemology: knowledge comes from an authority,
and that's that. Of course, it's normal at this age (grades 4-6), but
I'd like to do whatever I can do to move the kids on through the next
stages. It goes to the very nature of science: is it just a set of
results, or is it the process? It's both, of course, but the process
too often gets short shrift in education. It's difficult to
teach---it can't be a unit by itself, rather it has to be built in to
every science unit, which makes the logistics very difficult---and
it's difficult to write a test question about it. But it has to be
done.
If you're interested in what thoughtful people have discovered about
the stages of epistemology, you might start with this quick summary of William G. Perry's research.
The second group, grades 1-3, would have missed out on this except
that at some point I said, "Here's what I think is going on," and one
student said. "You're the teacher, you should KNOW what's going on" or
something like that. So that was a good chance to have a similar
discussion with that group.
Sunday, October 2, 2011
Floating and Sinking
Most kids love playing with water, and in hot weather water is a good thing to do science outdoors with. (Not to mention that the ocean is the theme in Primaria this year!) Discovering what sinks and what floats is a natural entry point for science because it is so simple that the youngest kids can appreciate it, yet it can lead to quite sophisticated concepts for the older ones who are ready to handle those. Furthermore, I designed this activity to lead naturally up to a submarine-building activity I want to do next time.
I started with just a simple glass of water visible. I asked each
child if they thought a wood chip would float or sink. For me, this
next step is really important. If the vote is not unanimous, I ask if
we can settle the issue just by counting the votes. Science is not a
democracy! We have to do the experiment and pay attention to the
results if we want to make any progress! And if the vote is unanimous, I
ask them if maybe we don't need to do the experiment. We agree
(sometimes with some nudging from me) that even if we all think it's
going to float, we should still do the experiment because sometimes we
could all be wrong in our predictions. I really want to emphasize
these aspects of the scientific method as early as possible, and this
activity is a good place to do it.
Then I repeat with several objects, such as a stone, a marble, a piece
of plastic, a bolt, a paper clip, etc. The kids have some idea that
lighter things are more likely to float, so the paper clip gives some
pause. I try not to use the word "density" because this means nothing
to the pre-K/K kids, but I do try to summarize that floating/sinking
is expected for something that is light/heavy for its size, not just
light/heavy in some absolute sense.
Then we get to the more interesting demo. (Some of them desperately
want to play with this stuff already, but I promise they can play if
they pay attention for just a bit longer.) I pull out a hard-boiled
egg and we see that it sinks. But if I add plenty of salt to the
water, the egg begins to float. This shows that the salt is mixing
with the water in a way which makes the water heavier. (By the way,
floating an egg is apparently how people used to determine they had
added enough salt to their pickling solution when making pickles.)
Then we repeat the whole thing with sand. Try as we might, the egg
does not float and the sand just collects at the bottom rather than
dissolving in the water. Here we have the observational basis for
some chemistry: salt in water forms a solution, but sand in water does
not. (I didn't state it this technically, but we did talk about how
ocean water behaves at the beach...the salt is an integral part of it,
as we can tell by its taste, but the sand is not.) We also have the
idea of different kinds of mixtures, which ties in nicely with the
previous pre-K/K science activity.
Finally we get to the play time. But this is serious play. I bring
out one tub of water in which I place some aluminum-foil boats.
Although they are metal, they do not sink. I challenge them to figure
out how to sink the boats. In parallel, a second tub contains empty
8-oz plastic soda bottles which I also challenge the children to sink.
The challenge aspect is really important. They come up with the ideas
and try them out. It seems like play time, but it has a purpose. This
particular challenge has the extra purpose that it builds up to the
future submarine activity.
With the foil, I have extra challenges ready for those who quickly
figure out how to sink the boats with stones. I challenge them to sink
the foil just by crumpling it up into a ball. It is surprisingly
difficult to do this; small air bubbles trapped in the foil are
surprisingly effective at floating it even after squeezing as hard as
possible. Some of them easily recognize that air bubbles must be the
problem, while others need some hints. The persistent ones finally
succeed in hammering out the air bubbles using anything vaguely
hammer-like. Meanwhile, others have gone in a slightly different
direction, crumpling the foil around a stone so that it forms a ball
with high average density.
With the plastic bottles, students take one of two initial strategies:
filling the bottles with water, or with stones/sand. Those who try
water see that water is not heavier than water, so that a waterlogged
plastic bottle still does not sink. Then they tend to start over with
stones/sand. However, the stone/sand strategy is surprisingly
ineffective. You can fill a bottle 1/4 full or even 1/2 or even 2/3 full of
stones/sand and it still doesn't sink. There's just too much air in
the bottle. However, few students have the patience (or the time left
in the activity) to fill the small-necked bottle completely with stones/sand.
They figure out (possibly with some hints) that they can
replace the bothersome air with water and finally get it to sink.
This is really good background for the submarine activity!
I think we spent 20 minutes with each group of about 5 kids, and that
was the perfect amount of time and the perfect size group. Larger groups could be
accommodated with more tubs of water; more than 3 kids per tub would not be good.
I started with just a simple glass of water visible. I asked each
child if they thought a wood chip would float or sink. For me, this
next step is really important. If the vote is not unanimous, I ask if
we can settle the issue just by counting the votes. Science is not a
democracy! We have to do the experiment and pay attention to the
results if we want to make any progress! And if the vote is unanimous, I
ask them if maybe we don't need to do the experiment. We agree
(sometimes with some nudging from me) that even if we all think it's
going to float, we should still do the experiment because sometimes we
could all be wrong in our predictions. I really want to emphasize
these aspects of the scientific method as early as possible, and this
activity is a good place to do it.
Then I repeat with several objects, such as a stone, a marble, a piece
of plastic, a bolt, a paper clip, etc. The kids have some idea that
lighter things are more likely to float, so the paper clip gives some
pause. I try not to use the word "density" because this means nothing
to the pre-K/K kids, but I do try to summarize that floating/sinking
is expected for something that is light/heavy for its size, not just
light/heavy in some absolute sense.
Then we get to the more interesting demo. (Some of them desperately
want to play with this stuff already, but I promise they can play if
they pay attention for just a bit longer.) I pull out a hard-boiled
egg and we see that it sinks. But if I add plenty of salt to the
water, the egg begins to float. This shows that the salt is mixing
with the water in a way which makes the water heavier. (By the way,
floating an egg is apparently how people used to determine they had
added enough salt to their pickling solution when making pickles.)
Then we repeat the whole thing with sand. Try as we might, the egg
does not float and the sand just collects at the bottom rather than
dissolving in the water. Here we have the observational basis for
some chemistry: salt in water forms a solution, but sand in water does
not. (I didn't state it this technically, but we did talk about how
ocean water behaves at the beach...the salt is an integral part of it,
as we can tell by its taste, but the sand is not.) We also have the
idea of different kinds of mixtures, which ties in nicely with the
previous pre-K/K science activity.
Finally we get to the play time. But this is serious play. I bring
out one tub of water in which I place some aluminum-foil boats.
Although they are metal, they do not sink. I challenge them to figure
out how to sink the boats. In parallel, a second tub contains empty
8-oz plastic soda bottles which I also challenge the children to sink.
The challenge aspect is really important. They come up with the ideas
and try them out. It seems like play time, but it has a purpose. This
particular challenge has the extra purpose that it builds up to the
future submarine activity.
With the foil, I have extra challenges ready for those who quickly
figure out how to sink the boats with stones. I challenge them to sink
the foil just by crumpling it up into a ball. It is surprisingly
difficult to do this; small air bubbles trapped in the foil are
surprisingly effective at floating it even after squeezing as hard as
possible. Some of them easily recognize that air bubbles must be the
problem, while others need some hints. The persistent ones finally
succeed in hammering out the air bubbles using anything vaguely
hammer-like. Meanwhile, others have gone in a slightly different
direction, crumpling the foil around a stone so that it forms a ball
with high average density.
With the plastic bottles, students take one of two initial strategies:
filling the bottles with water, or with stones/sand. Those who try
water see that water is not heavier than water, so that a waterlogged
plastic bottle still does not sink. Then they tend to start over with
stones/sand. However, the stone/sand strategy is surprisingly
ineffective. You can fill a bottle 1/4 full or even 1/2 or even 2/3 full of
stones/sand and it still doesn't sink. There's just too much air in
the bottle. However, few students have the patience (or the time left
in the activity) to fill the small-necked bottle completely with stones/sand.
They figure out (possibly with some hints) that they can
replace the bothersome air with water and finally get it to sink.
This is really good background for the submarine activity!
I think we spent 20 minutes with each group of about 5 kids, and that
was the perfect amount of time and the perfect size group. Larger groups could be
accommodated with more tubs of water; more than 3 kids per tub would not be good.
Friday, September 9, 2011
Icebreaking Activity: Mystery Tubes
Today was my first day with the elementary kids. This is a brand-new school with about 22 students total in grades 1-6, and there is flexibility to work with age-segregated or mixed-age groups. I did the mystery tube activity (with extension #1) because it's a good icebreaker, and it naturally comes first because it addresses the nature of science. (By the way, I discovered this activity when the folks from http://undsci.berkeley.edu/ came to UC Davis and conducted a workshop on science outreach. Their website is worth a look, especially the diagram showing the real process of science, which is the exact opposite of the cookbook 5-step procedure you see in most textbooks. But maybe that's another post.)
I chose mixed-age groups because I was afraid the younger kids would struggle with it, and could use assistance from the older ones (the activity is recommended for grades 6-16, but I was pretty confident that grades 4-6 could handle it well). There was a fair amount of awkwardness because everybody was new to the school, and there was no established pattern of working in groups; some students still didn't know some other students' names! Considering that, it seemed to go fairly well. While some younger kids did struggle, a few other younger kids just nailed it. So while I still wouldn't recommend it for a group younger than 4th grade, it was eye-opening to see some really good results from individual 2nd-graders. At the same time, I have to admit that there wasn't much discussion of concepts like "Test results sometimes cause scientists to revise their hypotheses." We were doing those concepts, but it was hard to discuss them in these mixed-age groups. In the future, if I have mixed-age activities I might think about how to "debrief" the older kids separately afterward, to discuss how they can take what they learned in the activity and generalize it to make it useful in other parts of their studies and their lives.
A few tips for those wishing to do this:
Most discussions of the process of science focus on the mechanics of it. Students pose a question ("How does this thing work?"), suggest hypotheses (saying "I think there's a knot inside" and drawing a diagram of where and what kind of knot), and then test their hypotheses ("If I pull here it should..."). This is all great, but teachers usually present it in a context where the correct answer is already known, or revealed at the end. If the answer is already known ("today we will measure the density of water"), the activity turns into a dry, dull exercise. If the answer is revealed at the end, the whole idea of science as an ongoing process of inquiry is subverted.
I chose mixed-age groups because I was afraid the younger kids would struggle with it, and could use assistance from the older ones (the activity is recommended for grades 6-16, but I was pretty confident that grades 4-6 could handle it well). There was a fair amount of awkwardness because everybody was new to the school, and there was no established pattern of working in groups; some students still didn't know some other students' names! Considering that, it seemed to go fairly well. While some younger kids did struggle, a few other younger kids just nailed it. So while I still wouldn't recommend it for a group younger than 4th grade, it was eye-opening to see some really good results from individual 2nd-graders. At the same time, I have to admit that there wasn't much discussion of concepts like "Test results sometimes cause scientists to revise their hypotheses." We were doing those concepts, but it was hard to discuss them in these mixed-age groups. In the future, if I have mixed-age activities I might think about how to "debrief" the older kids separately afterward, to discuss how they can take what they learned in the activity and generalize it to make it useful in other parts of their studies and their lives.
A few tips for those wishing to do this:
- have a bucket of threadable beads ready. These are handy for tying onto the strings in the models so they don't slip through the holes in the toilet paper tubes, as well as for connecting the strings in the interior (in any way they wish; I don't hint in any way that they should use the beads to connect the strings, but they get used because they're handy).
- I made tubes with different types of connections in the interior, because often when two groups of scientists think they're doing the same experiment, they're not really, due to some confounding variable. So I think having all tubes identical subverts the process-of-science aspect of the lesson, and this came in really handy when students begged me for the answer (I honestly didn't know the answer for each individual tube) or thought they figured out the answer and tried to tell everyone else rather than let the others experiment more.
- If you suspect groups might not function well as a group, it's ok to forget about "sharing findings" and the like. I wish I had more toilet paper tubes because many students wanted to make their own model, and I think that would have been better than forcing students to build models in groups. It's hard to wait for your turn at improving the model!
- We did it in 3 rotations of 20-25 minutes each. I think it needs a bit more time than that, like 30 minutes.
Most discussions of the process of science focus on the mechanics of it. Students pose a question ("How does this thing work?"), suggest hypotheses (saying "I think there's a knot inside" and drawing a diagram of where and what kind of knot), and then test their hypotheses ("If I pull here it should..."). This is all great, but teachers usually present it in a context where the correct answer is already known, or revealed at the end. If the answer is already known ("today we will measure the density of water"), the activity turns into a dry, dull exercise. If the answer is revealed at the end, the whole idea of science as an ongoing process of inquiry is subverted.
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