Hydrodynamics 101

Today I worked with the 1-2 graders to extend their concepts of force
and motion to include work and energy, and then, after the break,
fluid dynamics.

While waiting for the kids to come back from chorus to start science,
I sat with one child who hates chorus, and we interleaved the pages of
two phone books.  When science started, we talked about friction and I
used the phone books as a demo.  The friction of 200 pages trying to
slide past 200 other pages is so much that two strong adults cannot
bull the books apart.  Mythbusters had a great episode on this, in
which they used bigger (800 page?) phone books and couldn't pull them
apart even with cars.  They finally resorted to military tanks, and
found that it took a force of 8,000 pounds to separate the books!

We then talked about work, which is applying a force over some
distance.  Sitting in your chair, you are applying a force (your
weight) to the seat of the chair, but you are not doing work.
Exerting a large force (eg lifting a heavy weight) over a large
distance makes for a lot of work.  We related this to irrigation
because the kids are studying the community, and are about to learn
that farming really took off around here when large pumps became
available to move the water.

Energy is the ability to do work, and we spent a looong time talking
about different forms of (mostly stored) energy: food, chemicals,
light, heat, electricity, etc.  We spent a loooong time figuring out
what makes the electricity that comes to our houses!

Then came break.  After break we finished up a few more forms of
storing energy: magnets, rubber bands, springs, etc.  But mostly we
moved on to discussing how water moves (fluid dynamics).  I did the
"three-hole can" demo (see paragraphs 3-4 of this post) to introduce
pressure and the relationship between pressure and water height.  Then
I did the finger-on-the-straw demo (paragraph 6 of that post) to show
that the air also exerts pressure.  Next was a siphon tank demo, to
show that air pressure can sometimes help quite a bit in moving water.
This demo did not work well, possibly because of a leak, so see this
video.  Finally, I did the balloon in a bottle demo (paragraphs 6-8 of
the post linked to above) which is very analogous to the
finger-on-the-straw demo but far more dramatic....I could see Teacher
Ethan do a double-take when he first saw it.

Then I led the kids through designing different water systems on the
whiteboard.  I supplied basic ideas such as water flowing into a
shovel on a pivot, and asked them to predict what would happen (when
the shovel fills with water, that end pivots down, dumping the water
out).  We went through a bunch of these ideas, and I made sure to lead
them to realize the need for a pump to cycle the water back from the
bottom to the top.  By this point they were very eager to start
drawing their own ideas, which played right into my plan.  We had a
great time making posters of our ideas.  In the last five minutes, I
unveiled the hydrodynamics kit which they will use in free-choice time
(or whenever Teacher Pa deems fit) to actually implement their ideas.

Overall, I think it went really well.  We discussed a lot of ideas,
without overwhelming the kids, and the poster-drawing session was both
fun and educational.