That sounds like a nice project. I think that you can teach 2nd graders
something about energy conservation. In other words, you can show them
that when one form of energy is reduced another increases. Of course,
you can only show this for a few forms. More importantly, they have no
prior reason to call different forms of energy the same thing. So I
think the demonstration that kinetic energy can go to potential energy
or that large scale energies can be lost as things heat up or that
light absorption leaves things hotter, etc should come first. That
would get the idea across that something or other about these effects
is in common, changing forms but not going away. Then maybe you can say
that this something gets called energy. That way the idea would be
first, and mere names second.
Here are some examples:
bouncing ball, swinging pendulum, .... When the thing is high it
goes slow, when it's low it goes fast. As if somehow you could trade
height for speed. But then it seems that gradually both the height and
the speed run down.
Show that the same thing (called friction) that tends to make things stop sliding or bouncing leaves them a little hotter.
Show crank-powered generator and light. Note that you could also
power generator with fallling stuff, like a water wheel. Draw
connections with height/speed.
Note that the light feels warm- draw connections with warmth from friction.
Note that batteries run down- and you can charge them up with a crank-powered generator.
So by this point it may be OK to say that you're talking about different forms of energy.
Maybe show some chemical energy- burn something, get heat and
light, maybe run a toy steam engine. You could even use it to lift
things. You can also talk about energy contained in food here, and how
the body uses it to keep warm and to do stuff like run around and lift
things. 2nd graders have lots of energy themselves (except when they
don't), and the foods they eat have a lot to do with that.
Now you may be ready to ask if there's usable chemical energy
stored in water- if it will burn. When they figure out the answer is
no, they will be more educationally advanced than certain prominent
politicians who say that we can obtain our future chemical energy from
the hydrogen in water.
(published on 10/22/2007)