Center of gravity is a difficult concept for kids to grasp. This experiment can help, though.
It's scientastic! Okay, that's not a real word, but it should be.
What You Need
An unsharpened pencil
1 piece of wire (ours was 16 gauge) about 12-14 inches long
2 wooden clothespins
Take a straight length of wire and put the pencil on top of it in the center, about an inch away from the end of the eraser. Holding the pencil and wire in place, bend the left "arm" of the wire over top the pencil. Do the same with the right "arm" of wire.
Now arc the two ends of wire downward slightly and clip the clothespins on each end.
Take the pencil and try to balance the eraser on your nose. Adjust the wire (closer to the eraser), its curve, or the position of the clothespins in necessary. Once you get the position right, you'll be surprised at how easy it is to balance ... for 10 seconds or even longer!
Why it Works
It's easier to balance something when you lower its center of gravity, which is precisely what the weights (i.e. wire and clothespins) accomplish. Another example of this is when high-wire walkers carry a long pole to help them balance better.
This great idea came from Jordan D. Brown's awesome book. Check it out!