Rock Solid

2 plastic cups
2 cups water
microwave oven
oven mitts
1) Pour one cup of water into each cup. Place one cup into the freezer a few days before doing this demonstration to ensure that the water is frozen solid.
2) Place both cups of water in front of you. Ask the girls what they think would happen if you put a cup of water and an equal sized cup of ice into the microwave. They will probably say that the ice will melt and the water will get hotter.
3) Put both cups into the microwave. Set it for 2 minutes on high. Immediately start the microwave.
4) After the 2 minutes are up, put on the oven mitts and pull out both cups. Explanation: The molecules in ice are packed tightly together, and the vibrate. Water molecules also vibrate, but they also move around, rotate. The hotter the water, the faster they move. Microwaves heat foods by speeding up the rotation of the molecules. Since ice molecules don't rotate, the microwave doesn't affect them.