Understanding the gravity of the situation

Last Friday with the 1-2 graders we reviewed and extended our
observations of force and motion which we began two Fridays ago,
before the Yosemite trip.  Because it had been two weeks, we started
with quite a bit of review, which I did by asking the kids questions
rather than lecturing to them.  We observed the motion of a rolling
ball in order to change the context from last time (when we used a
hoverpuck or a marble shot out of a blowgun).

I had them observe and draw some motions.  This addressed California
Grade Two science standards 1a and 1b, as well as built the case for
the following argument.

By observing a ball thrown up in the air, we concluded that there is a
force on it even when I am not touching it, and that that force is
simply gravity.  I then repeated the donutapult demo to refresh their
thinking on how something goes in a circle only when there is a force
on it; if there is no force on it, it will go off in a straight line.
Then we talked about the Moon and how there must be a force on it
because it goes in a circle around the Earth.  That force is also
gravity!

(I think the following was too advanced, but we did discuss it.
Gravity always points to the center of the Earth.  One student is
going back to Korea soon, so I drew Davis and Korea on a globe and
showed how this must be the case.  Then I noted how the force on the
donut also points to the center of its "orbit" because that is the
only direction the string can pull.  So there is very strong reason to
think that the force on the Moon is Earth's gravity, the same force we
know and love, that makes things fall when we drop them! [Standard 1e])

After the break we discussed how to send forces in different
directions and in different amounts by using simple machines such as
levers, pulleys, and gears.  I had brought in the Gears!Gears!Gears!
toys earlier in the week, so they easily got the basic idea of this
standard (1d).  But I lost them    when I got into the details of
levers...they weren't able to predict where to place a lever and a
fulcrum to perform a given task, nor were they able to draw arrows
indicating the sizes of the forces at the different ends of the lever.
And I didn't really have the equipment handy to do real hands-on work
with that, so I may do this again this Friday with better equipment.