Planets and their orbits

Today I brought the coin funnel to Primaria and we learned how orbits work.  One four-year-old came up with Kepler's 3rd Law all by himself!  With 6-8 kids in each group I organized it by having each child raise a quiet hand, tell me something they know about planets or the Sun, and then I gave that child a marble to roll in the well.  That gave me a chance to comment on what we could learn from each marble.  Depending on how it was thrown, the lesson could have been about escape velocity, about planets not falling straight into the Sun, about all the planets going around in the same direction, etc. Most of the time we pretended the Sun was at the center but if you want to make it more exciting you can pretend it's a black hole. 

Then  we shifted gears and built a scale model of the solar system: I showed a basketball representing the Sun, and I laid out various objects (a tomato, a grape, a small candy, etc) for them to choose which one they thought was the right size to represent Jupiter, the Earth, etc.   The correct answers are truly amazing: learn more at this well-written site. We didn't have time to go outside and put the correct distances between the planets, but I did describe the highlights of that aspect: Earth would be roughly in the office if we were with the Sun in the P1 room.

Aside on teaching and learning: one aspect of orbits is that all objects in a given orbit go at the same speed, regardless of their mass (technically, as long as the mass is much smaller than the mass of the thing being orbited).  To reinforce that, I dropped two marbles of very different mass and asked which one would hit the ground first.  Of course, many had the misconception that the heavy one would hit first.  I remark on it now because I had done the same demo with the same kids eight weeks ago in a slightly different context, so it's clear that they forgot.  These misconceptions are persistent!

Whirled Series

Today at the elementary we explored series vs parallel circuits.  I
drew circuits on the board and part of my challenge to the kids was to
figure out how to build what I had drawn.  This led to some conceptual
breakthroughs; for example, some of them had not imagined that they
could twist the ends of three wires together at the same time to make
a more complicated circuit, but they were driven to this idea by the
challenge of building what I had drawn on the board.

The first pair of circuits compared parallel vs series switches rather
than light bulbs (of course there was still one light bulb in the
circuit so we could see when current was flowing).  This reinforced
the basic concept that you need a complete circuit from the positive
battery terminal to the negative one: with switches in series you need
both of them closed, but with switches in parallel you only need one
or the other.  As a corollary, an extra wire dangling off a closed
circuit (which is basically what you have in a parallel-switch
arrangement when one switch is closed and the other one is open)
doesn't hurt anything.

Next, we compared parallel vs series light bulbs.  Students saw that
two light bulbs in series (with a single battery) were quite dim, but
that in parallel they were much brighter.  (This one sentence
summarizes at least 10 minutes of work on their part!)  In thinking
about how to explain this beforehand, I thought a real explanation
involving current and voltage would just be too complicated, but I
didn't want to dumb it down too much either.  As it happened, when the
time came things were so hectic as I flitted from group to group that
I had to settle for something quick: with two paths in parallel we can
get twice the flow.  (This doesn't really explain anything because
there are still parts of the circuit which are NOT parallel...but I
think it was suitable for this age.)

Finally, we used two batteries to power our two light bulbs in series.
I had them compare two ways of connecting the batteries: top of one
touching bottom of the other, and bottoms together.  To explain the
result, I again shied away from voltage numbers and instead stuck to
the concepts they had thought about a lot: current wants to flow from
+ to -, so when you put them with bottoms together the two batteries
want the current to flow in opposite directions and nothing gets done.

Of course, it would have been instructive to compare two batteries in
parallel, but we did not have time.  Furthermore, to explain that one
I think they really would need a full treatment of current vs voltage.

One of the kids discovered how to make a short circuit, so I explained
that to the whole group.  That was something I should have planned do
even if no one had discovered it.

All in all, these activities were at just the right level in the sense
that they couldn't always predict what was going to happen, so that
the experiments did contribute to their understanding; yet the
experiments were not so far beyond their understanding as to be
frustrating.  There were elements of frustration, but they had more to
do with the assembly of the circuits.  Ease of assembly was much
improved over last time because I had soldered wires to many light
bulbs and batteries, but the circuits were also much more complicated.
Next year I will invest in real electronics kits with breadboards and
such.

Sparking an Atttraction

Today at the elementary we built electromagnets.  First I asked each table to prove that they were ready by getting a light bulb to light up given a battery and a few wires.  From their time with teacher Lorie they should have learned that electricity has to travel in a circuit, and most of them were able to do that fairly quickly.  To move on to the electromagnet, each table had to pass a test: if they switch the wires on the light bulb, will it still light up?  Many of them said no quite confidently, but regardless of what they predicted I made them do the experiment.  I then explained how the bulb (a small incandescent bulb for a flashlight or nightlight...the simplest, cheapest type of light bulb) works.  It heats up when electric current passes through, and gets so hot it glows.  This mechanism is so simple that it doesn't even matter which direction the current passes through.  Fancier light bulbs (LEDs) might be more persnickety.

For the electromagnet I told each table to wind a wire tightly many times around a 10d nail.  (Unlike the website linked to in the previous sentence, I didn't bother with switches; we just held things together with electrical tape and/or fingers.) As they finished, some of them asked me what to do next, and others just started trying things.  I gave only vague hints to those who asked, such as "Figure out how to pass electricity through it."  The trick is to make a complete circuit, just as with the light bulb, but they really had to think and experiment (and receive some more hints) before getting it.  This just shows how hard it is to transfer knowledge learned in one context to another context.

After the first session, I figured out that the best way to respond when asked what to do with the wire-wrapped nail is to ask them to check if it's magnetic yet.  This serves two purposes (1) makes them develop a procedure for checking if it's magnetic, which I wanted them to do at some point anyway (picking up a paper clip is the best test I know of); and (2) see that you need flowing current to make the electromagnet work.  After some current flows, the nail tends to get permanently magnetized, making it less obvious later on that current is necessary.  Therefore it's best to demonstrate early on that there is no magnetism.  Also, if you reuse materials from earlier experiments you might well get materials that have accidentally been permanently magnetized.  You'll want to check for this before handing materials out.

For tables which had time left after proving to me that their electromagnet functioned, I gave additional challenges.  Some I challenged to make 2 light bulbs light up.  To others I gave permanent magnets and asked them to figure out how to magnetize a nail without electricity.

All in all this was a pretty good 45-minute activity, with no lecture by me (although it is good to emphasize at some point that this demonstrates that there is a connection between electricity and magnetism).  The one downside was that any circuit more complicated than a single bulb or nail was impossible to keep together with tape and fingers, and one of the younger kids got very frustrated even with a single bulb.  If I were to do more circuit experiments, I would prep by soldering wires on to the light bulb and battery terminals.  This had crossed by mind beforehand, but I thought that this might be giving too much away; I wanted them to figure out the relevant parts of the light bulb.  So in the future I might have one set of bare bulbs for beginners, and one set of bulbs with leads for those who want to make more complicated circuits which don't fall apart.  (Those who don't like soldering might consider using sockets and wires with crimp connections, etc.)

Science in the River City

K12 teachers in the Sacramento area should check out the Science in the River City professional development workshop.  It happens roughly monthly throughout the school year and the last one this year is coming up on April 24.  Teacher feedback indicate that it's pretty useful.

More static electricity

Today I visited Primaria and did an abbreviated, simplified version of the static electricity work I did with the elementary.  The bare essentials are to demonstrate attraction (hair to rubbed balloon) and then show that, counterintuitively, two rubbed balloons do not attract doubly but actually repel.  This leads us to conclude that there must be two kinds of charge and that like repels like.  I also did the deflection-of-water demo because it's too cool to miss, and it demonstrates that all things contain two kinds of charge even if on balance they are uncharged.

I also emphasized that electricity is stronger than gravity (a wimpy balloon overcomes the entire Earth's pull of gravity on the hair) so they could be hurt if they play with it without a grownup around.

One thing I did differently is that I immediately made a connection to magnetism.  They had played with magnets with their regular teacher, so I thought they might be able to make the connection themselves.  But when I asked what other thing (other than static electricity, whose dual nature we had just established) sometimes attracts and sometimes repels, they drew a blank.  I reminded them of magnets and noted the similarity between +/- and north/south, saying that there is a deep connection but they might have to be older to understand it.

That led nicely to the last 5-10 minutes, in which they played with magnets and static electricity, doing their own experiments.  There are a lot of fun things they can build, like anti-gravity devices (opposing ring magnets threaded onto a vertical pencil, which keeps them from sliding sideways), magnet bombs (stacks of opposing magnets forced together by hand, then suddenly released), and remote-control devices (a magnet on top of a tray manipulated by an unseen magnet below the tray).  They just need a little bit of hinting to start exploring the possibilities.

Addendum: the effectiveness of the static electricity demos varies quite a bit from day to day depending on the humidity.  If you have any flexibility, save it for a dry day.

True North

Today at the elementary school we became familiar with magnets.  Grades 1-3 did more of an exploration than a specific lab or task.  I was amazed at how excited they were to play with magnets!  They discovered all kinds of creative things like an "antigravity" device and moving a magnet on a desk using another magnet under the desk, which could not be seen by casual spectators.  I tried to structure their exploration around some basic questions asking how magnets behave in ways similar to and different from charged objects, which was our previous session, and after a lot of exploration we discussed this as a group.    In addition to run-of-the-mill magnets, I brought in one really strong magnet, some small pieces of steel, a plastic case with iron filings, and some compasses.  I sketched how Earth has a magnetic field much like the one shown by the iron filings around a magnet, but we did not talk about compasses much more than that. (I know the kids had some training in the practical use of compasses at their field site. )  The compasses were used mostly as devices which could be spun like crazy by the handheld magnets!

For grades 4-6 I had planned a more directed activity after a shorter period of exploration, because most of them had already played with magnets at some point.  The activity was to build a compass by magnetizing a small piece of steel and then allowing the small piece to move freely.  The moving-freely part was supposed to be accomplished by floating it in water, which a small piece of steel can actually do thanks to surface tension (which formed a mini-lesson in itself).  It seemed pretty easy to get it to float when I practiced it at home, but it was very difficult at school.  The kids got discouraged and played with other aspects of magnets when I wasn't at their table to help them.  I still think it's a good lab, but next time I have to find even smaller pieces of steel, or some other way to remove friction.  I made an on-the-fly attempt at removing friction by hanging it on a string, but the string was too stiff to allow it to rotate freely.  Some people suggest sewing needles, but that seemed a bit dangerous.  I guess I could just blunt the needles before use.

This blog entry is a bit short, without the usual diagrammatic explanation of everything we discussed, but I have to save time this week.  Someday I hope to write a longer explanation of everything we talked about.  We did discuss in quite a bit of detail, because we had 45 minutes per group, which is now the norm since about mid-February.  This amount of time really facilitates thought and discussion.

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.