A very entertaining demo that illustrates that metals expand at different rates when they are heated. Two metals are annealed together, side by side. The end of the strip is placed in a propane flame and pushed forward. As the metals are heated they begin to expand at different rates, causing the strip to bend, or bow. Turn the faucet on and push the heated strip through the water, and as the water cools, the metal returns to its original shape. Great introduction to the idea that solids expand when they are heated and contract as they cool.
LL Demos & Labs: Bimetallic Strip.