2. a. Metal particles move more rapidly when heated so the particles moved further apart. b. Metal particles move less rapidly when heated so the particles moved closer together. c. The metal particles did not move. The water loosened the lid. d. The metal particles melted because the water was so hot.

3. a. expansion b. contraction c. diffusion d. participation

5. a. Metal reacts to heat. b. Metal particles expand when heat energy is added and contract when heat energy is removed. c. Metal is a good conductor of electricity. d. Bimetal strips are magic.

7. a. This observation is evidence that air is in the gas phase of matter. b. This observation is evidence that heat makes air expand. c. This observation is evidence that warm air diffuses faster than cold air. d. This observation is evidence that air particles are in constant motion.

11. a. Bar graph b. Line graph c. Pie Graph d. What Graph?