This relates to our recent themes of solid/liquid/gas and pressure, but mostly it was for fun. I brought a steel tube just a bit larger than a tennis ball, a 16-oz plastic soda bottle, a tennis ball, and some liquid nitrogen. After the usual LN2 demos, we went outside to make the cannon. I found a large object to hold the tube upright, then I loaded the bottle with about 4 oz of LN2, screwed the cap on tightly, dropped the bottle into the tube, and dropped the tennis ball on top. Then we waited for the liquid nitrogen to boil into gas, which would make the pressure inside the bottle roughly 100 times atmospheric pressure. It took about 5 minutes, and then the bottle exploded, propelling the ball hundreds of feet into the air and out into the neighboring field. Even the ripped-apart bottle shot up in the air, about 50 feet. It was awesome!
I had a second bottle and ball, but I was too greedy. I put in about 8 oz of LN2 to get a bigger boom, but after a 7-8 minute wait we heard a hissing. The bottle had a nonexplosive leak. Since it was starting to rain as well, we went inside, figuring it would not blow. But after another 7-8 minutes, we heard it blow. Bottom line: it's awesome with just 4 oz.
Friday, December 21, 2012
A Sense of Scale
Today we covered three small topics. It's my last day with the 1-2
graders (I will rotate to the upper graders), and also the last day
before Christmas vacation, so I tried to squeeze in several fun things
and also answer some of the questions which arose last week. So we
didn't go super-deep in any one topic, but we had a blast.
We started with a movie: the ten-minute 1977 classic Powers of Ten by
Charles and Ray Eames. I wanted to show this movie because the kids
had many questions last time, when I mentioned galaxies but didn't
have time to really explain them. This movie steadily zooms out from
a person on Earth to show how big and how far apart astronomical
objects are. The movie then zooms progressively in to show the sizes
of microscopic things. (Note: if you want more snazzy modern special
effects you might try the more recent Cosmic Voyage, but Powers of Ten
feels more intense.) I stopped the movie many times to answer
questions as they arose, but eventually there were too many questions.
We had four 3-4 graders in the room, and I will be doing astronomy
with them in the spring. It looks like showing this movie would be a
good way to start my three months with them. They could generate
questions, and we could take our time answering them. The best
question today was, "How do we know all this?" and I hated not having
time to give a real answer. My three months of astronomy with the 3-4
graders will be the answer to "How do we know all this?"
I then showed a website for visualizing the sizes of things, where you
control the zoom. This is a great site for showing how much
bigger the Sun is compared to Earth, how much bigger some stars are
compared to the Sun, etc. But be warned: they do NOT show the space between these objects, so don't be fooled. The space in between stars
is VERY, VERY BIG compared to the stars themselves.
Apart from that, it's a great tool. (One caveat: I did not zoom out all the way to the "estimated size of the universe"...there is no estimated size of the universe.) Exploring this site also generated many questions, so that may also be a good icebreaking activity. Because you can zoom in as well, it could even be a good icebreaker for life sciences as well.
A few more links for interested parents:
Activity number three will be the next blog post.
graders (I will rotate to the upper graders), and also the last day
before Christmas vacation, so I tried to squeeze in several fun things
and also answer some of the questions which arose last week. So we
didn't go super-deep in any one topic, but we had a blast.
We started with a movie: the ten-minute 1977 classic Powers of Ten by
Charles and Ray Eames. I wanted to show this movie because the kids
had many questions last time, when I mentioned galaxies but didn't
have time to really explain them. This movie steadily zooms out from
a person on Earth to show how big and how far apart astronomical
objects are. The movie then zooms progressively in to show the sizes
of microscopic things. (Note: if you want more snazzy modern special
effects you might try the more recent Cosmic Voyage, but Powers of Ten
feels more intense.) I stopped the movie many times to answer
questions as they arose, but eventually there were too many questions.
We had four 3-4 graders in the room, and I will be doing astronomy
with them in the spring. It looks like showing this movie would be a
good way to start my three months with them. They could generate
questions, and we could take our time answering them. The best
question today was, "How do we know all this?" and I hated not having
time to give a real answer. My three months of astronomy with the 3-4
graders will be the answer to "How do we know all this?"
I then showed a website for visualizing the sizes of things, where you
control the zoom. This is a great site for showing how much
bigger the Sun is compared to Earth, how much bigger some stars are
compared to the Sun, etc. But be warned: they do NOT show the space between these objects, so don't be fooled. The space in between stars
is VERY, VERY BIG compared to the stars themselves.
Apart from that, it's a great tool. (One caveat: I did not zoom out all the way to the "estimated size of the universe"...there is no estimated size of the universe.) Exploring this site also generated many questions, so that may also be a good icebreaking activity. Because you can zoom in as well, it could even be a good icebreaker for life sciences as well.
A few more links for interested parents:
- http://www.nikon.com/about/feelnikon/universcale/ is a similar idea as the previous link but with a different feel. It's worth checking out, but it mostly focuses on microscopic things rather than astronomical things (it has a few mistakes too.
- http://www.wordwizz.com/pwrsof10.htm is another site along these lines; it's not as pretty as the previous two, but it does properly show the vast space between things.
- http://www.powersof10.com/ is a site (currently in beta) by the Eames Office. I just discovered while gathering links for this post, so I can't say much about it other than it looks promising.
Activity number three will be the next blog post.
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....
Tuesday, December 11, 2012
Written in Fire
We split Friday morning into two unrelated activities: sound, and a
review of states of matter.
For sound, I brought a lot of toys: tuning forks, a xylophone, etc.
The standard I wanted to cover was "sound is made by vibrating objects
and can be described by its pitch and volume" so I started with the
tuning forks and steered a discussion of pitch and volume (they
noticed right away that the tuning fork vibrated). It was pretty
funny, as the kids focused entirely on pitch, and I could not get them
to guess, despite numerous hints, that VOLUME or LOUDNESS was a
difference between the two sounds I was playing, even when they were
the same pitch. (It didn't help that when I really whacked the
xylophone hard, it did change its pitch somewhat as the whole thing
shook.)
Then I turned the kids loose to play with the tuning forks, the
xylophone, and a few other toys:
Then we got back together as a group and talked about how our
observations are explained by sound being a wave. To visualize this,
Teacher Pa and I stretched a very long spring (like the coiled wire
that ran from a telephone to its handset, in the old days before
wireless phones) across the room, and I bunched up my end and released
the bunch (still holding my end). It was very clear that a pulse
traveled the length of the spring to Teacher Pa, and it bounced off
her and came back to me. I related this to the behavior of the
thunder stick (what do you think happens if you hold the spring rather
than the tube?) We also had two plastic cups linked by a string, and
Teacher Pa gave a chance for each kid to hear her voice carried along
by the string.
For the piece de resistance I brought a Rubens tube. This is a long
tube with many small holes drilled in a line, connected to a propane
tank. You turn the propane on and light the holes so it looks like a
row of 100 candles. Now comes the cool part: there is a speaker
attached to one one. Hooking it up so that music plays on the speaker
makes waves in the propane in the tube and pushes it out more in some
places than in others. The fire dances to the music! Music has lots
of tones mixed together though, so it's best to start with some pure
tones. I brought a function generator to generate tones of any
desired frequency and amplitude, which is a really great
visualization. Into and beyond break/snack time, kids and teachers
from all the rooms in the school were cycling through our room and
watching this. The upper graders were transfixed. They wanted to try
all their favorite songs. We found that (to the dismay of some)
Gangnam Style was a really good one for making the flames dance. We
eventually had to shut it down at close to 11:30, about an hour after
I first fired it up. To see a Rubens tube in action yourself, check out this educational video.
From 11:30 to 12:15, Teacher Pa led us through some activities
reviewing the states of matter. For example, she passed out images of
many different things and the kids had to paste them onto a poster in
the Solid column, the Liquid Column, or the Gas column. This was
really useful for the kids, and for the teachers to assess how much
the kids got it. In discussing this with the kids, we found a great
idea for next week: clarifying what we mean by "amount" or "size" of
something. The difference between "size" (which most people would
take to mean a diameter, a distance across, or a height) and volume
came up in the context of gas expanding to fill its container, and it
was clear that we didn't have time to address it that day. So we'll
do that next time. It will play into one of the Investigation and
Experimentation standards about measuring length and volume, but I
want to keep it conceptually rich as I did last year.
review of states of matter.
For sound, I brought a lot of toys: tuning forks, a xylophone, etc.
The standard I wanted to cover was "sound is made by vibrating objects
and can be described by its pitch and volume" so I started with the
tuning forks and steered a discussion of pitch and volume (they
noticed right away that the tuning fork vibrated). It was pretty
funny, as the kids focused entirely on pitch, and I could not get them
to guess, despite numerous hints, that VOLUME or LOUDNESS was a
difference between the two sounds I was playing, even when they were
the same pitch. (It didn't help that when I really whacked the
xylophone hard, it did change its pitch somewhat as the whole thing
shook.)
Then I turned the kids loose to play with the tuning forks, the
xylophone, and a few other toys:
- bathtub flutes, which you can fill with water and then blow on while they drain. The pitch corresponds (inversely) to the length of the wave which just fits in the air-filled part of the tube, so the pitch starts out high and then drops as the water level drops.
- plastic hoses flared on one end. You whirl them around quickly, and they make an eerie whistling noise. Same principle as the flute, only this time the length is fixed, and we make the air flow by whirling the tube rather than blowing on it.
- a "thunder stick" which is a long spring connected to a drum membrane stretched over one end of a tube (the other end is open). Holding the tube and shaking it results in surprisingly loud boingy sounds.
Then we got back together as a group and talked about how our
observations are explained by sound being a wave. To visualize this,
Teacher Pa and I stretched a very long spring (like the coiled wire
that ran from a telephone to its handset, in the old days before
wireless phones) across the room, and I bunched up my end and released
the bunch (still holding my end). It was very clear that a pulse
traveled the length of the spring to Teacher Pa, and it bounced off
her and came back to me. I related this to the behavior of the
thunder stick (what do you think happens if you hold the spring rather
than the tube?) We also had two plastic cups linked by a string, and
Teacher Pa gave a chance for each kid to hear her voice carried along
by the string.
For the piece de resistance I brought a Rubens tube. This is a long
tube with many small holes drilled in a line, connected to a propane
tank. You turn the propane on and light the holes so it looks like a
row of 100 candles. Now comes the cool part: there is a speaker
attached to one one. Hooking it up so that music plays on the speaker
makes waves in the propane in the tube and pushes it out more in some
places than in others. The fire dances to the music! Music has lots
of tones mixed together though, so it's best to start with some pure
tones. I brought a function generator to generate tones of any
desired frequency and amplitude, which is a really great
visualization. Into and beyond break/snack time, kids and teachers
from all the rooms in the school were cycling through our room and
watching this. The upper graders were transfixed. They wanted to try
all their favorite songs. We found that (to the dismay of some)
Gangnam Style was a really good one for making the flames dance. We
eventually had to shut it down at close to 11:30, about an hour after
I first fired it up. To see a Rubens tube in action yourself, check out this educational video.
From 11:30 to 12:15, Teacher Pa led us through some activities
reviewing the states of matter. For example, she passed out images of
many different things and the kids had to paste them onto a poster in
the Solid column, the Liquid Column, or the Gas column. This was
really useful for the kids, and for the teachers to assess how much
the kids got it. In discussing this with the kids, we found a great
idea for next week: clarifying what we mean by "amount" or "size" of
something. The difference between "size" (which most people would
take to mean a diameter, a distance across, or a height) and volume
came up in the context of gas expanding to fill its container, and it
was clear that we didn't have time to address it that day. So we'll
do that next time. It will play into one of the Investigation and
Experimentation standards about measuring length and volume, but I
want to keep it conceptually rich as I did last year.
Sunday, December 2, 2012
It's a Gas
Last Friday I discussed solids, liquids and gases with the 1-2
graders. I brought in samples of each to provide a basis for
discussion. In addition to the obvious (a wood block, a glass of
water, a balloon filled with air), I brought some things designed to
stimulate their thinking: a rubber band, a cloth, a balloon filled
with water, and sand. We took about 35 minutes to discuss how we
could define solid, liquid, and gas. It's not as obvious as you might
think at first; for example, if liquids and gases flow unlike solids,
why can you pour sand? Does that mean sand is a liquid? I wish I had
time to document our discussion here! I'll just document that at the
end it is important to note that substances can change from one state
to another and back depending on the temperature. Water is the best
example: we talked about glaciers, lakes and rivers, and rain, which
they have already studied this year. But it's worth mentioning other
examples lest they think this is peculiar to water. The metal parts
of their desks were once liquid, which was poured into a mold.
In the hour after snack break, we did a more extensive experiment. I
handed out cups with (small amounts of) vinegar, and they wrote down
observations: it smells funny, it's liquid, etc. They did the same
with cups of (small amounts of) baking soda. They also weighed both
cups on the scale together. I found it easier to use a kitchen scale
which read grams rather than a scientific scale which reads to a
hundredth of a gram, so that I didn't have to explain decimal points.
Then they mixed the two and observed the reaction. They drew it and
wrote down their observations. Then we observed what was left: it
smelled different, and it weighed less (typically by a few grams out
of about 100 to start with). We figured out together where the
missing grams went: when the bubbles popped, the gas escaped (in the
earlier session we had talked about this with respect to balloons).
They did all of the above in small groups (individuals, actually,
because we had three adults and four kids!), but we spent a few
minutes at the end summarizing what we learned. One child wrote on
his worksheet "V [vinegar] +B [baking soda] = air" so that was a great
place to start discussing. Did we know that gas was air? What else
was produced? They seemed to not recognize that what was left in the
cup was also a result of the reaction and should go on the right hand
side of the equation. Is the stuff left in the cup just leftover
vinegar and baking soda? No, because it smelled different. The
equation written by the child was a great insight, but by the end we
produced a more accurate equation with more words.
Finally, it is important to note that this is a chemical reaction: we produced
some new kinds of substances! This is very much unlike water going
from liquid to gas, which they might have in mind as a model
transformation of a substance. Because some of them like explosions,
I related it to the chemical reactions in explosions. Explosions (ok,
most explosions) are chemical reactions too; they just happen faster
and give off more heat.
Then the kids spent 5-10 minutes drawing a scene with as many
different solids, liquids, and gases as they could think of, labeling
each. At the very end, I rewarded them with a show of Diet Coke and
Mentos fountains. It was raining, so I bought 1-liter bottles whose
fountains could be contained in the sink. This turned out to be a
great capstone for the morning, as carbonation seemed to be a new idea
to many of the kids. We tasted the Diet Coke before and after
defizzing to see the effect of gas on our taste buds. We also
discussed how the gas was in the liquid and normally comes out slowly
(you can see small bubbles coming out when the cap is off) but comes
out quickly with the help of Mentos.
For those who want more: Here is an entertaining video of Diet Coke and
Mentos reactions. If you want to go beyond entertainment and learn more
about why it happens, you should watch the Mythbusters episode on Diet
Coke and Mentos. They do experiments with different ingredients to figure
out what is most responsible for the reaction.
graders. I brought in samples of each to provide a basis for
discussion. In addition to the obvious (a wood block, a glass of
water, a balloon filled with air), I brought some things designed to
stimulate their thinking: a rubber band, a cloth, a balloon filled
with water, and sand. We took about 35 minutes to discuss how we
could define solid, liquid, and gas. It's not as obvious as you might
think at first; for example, if liquids and gases flow unlike solids,
why can you pour sand? Does that mean sand is a liquid? I wish I had
time to document our discussion here! I'll just document that at the
end it is important to note that substances can change from one state
to another and back depending on the temperature. Water is the best
example: we talked about glaciers, lakes and rivers, and rain, which
they have already studied this year. But it's worth mentioning other
examples lest they think this is peculiar to water. The metal parts
of their desks were once liquid, which was poured into a mold.
In the hour after snack break, we did a more extensive experiment. I
handed out cups with (small amounts of) vinegar, and they wrote down
observations: it smells funny, it's liquid, etc. They did the same
with cups of (small amounts of) baking soda. They also weighed both
cups on the scale together. I found it easier to use a kitchen scale
which read grams rather than a scientific scale which reads to a
hundredth of a gram, so that I didn't have to explain decimal points.
Then they mixed the two and observed the reaction. They drew it and
wrote down their observations. Then we observed what was left: it
smelled different, and it weighed less (typically by a few grams out
of about 100 to start with). We figured out together where the
missing grams went: when the bubbles popped, the gas escaped (in the
earlier session we had talked about this with respect to balloons).
They did all of the above in small groups (individuals, actually,
because we had three adults and four kids!), but we spent a few
minutes at the end summarizing what we learned. One child wrote on
his worksheet "V [vinegar] +B [baking soda] = air" so that was a great
place to start discussing. Did we know that gas was air? What else
was produced? They seemed to not recognize that what was left in the
cup was also a result of the reaction and should go on the right hand
side of the equation. Is the stuff left in the cup just leftover
vinegar and baking soda? No, because it smelled different. The
equation written by the child was a great insight, but by the end we
produced a more accurate equation with more words.
Finally, it is important to note that this is a chemical reaction: we produced
some new kinds of substances! This is very much unlike water going
from liquid to gas, which they might have in mind as a model
transformation of a substance. Because some of them like explosions,
I related it to the chemical reactions in explosions. Explosions (ok,
most explosions) are chemical reactions too; they just happen faster
and give off more heat.
Then the kids spent 5-10 minutes drawing a scene with as many
different solids, liquids, and gases as they could think of, labeling
each. At the very end, I rewarded them with a show of Diet Coke and
Mentos fountains. It was raining, so I bought 1-liter bottles whose
fountains could be contained in the sink. This turned out to be a
great capstone for the morning, as carbonation seemed to be a new idea
to many of the kids. We tasted the Diet Coke before and after
defizzing to see the effect of gas on our taste buds. We also
discussed how the gas was in the liquid and normally comes out slowly
(you can see small bubbles coming out when the cap is off) but comes
out quickly with the help of Mentos.
For those who want more: Here is an entertaining video of Diet Coke and
Mentos reactions. If you want to go beyond entertainment and learn more
about why it happens, you should watch the Mythbusters episode on Diet
Coke and Mentos. They do experiments with different ingredients to figure
out what is most responsible for the reaction.
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