Cold air molecules collide to generate heat energy. Cold energy in the room transforms into heat energy. The room becomes warmer as heat energy is added to the room. The room becomes warmer as cold energy is pushed out of the room.
I gave my students this multiple choice question: The temperature in a classroom is 15°C (59°F). The teacher turns the thermostat to 20°C (68°F) and keeps the door closed. Which of the following statements best describes the change that occurs as the temperature in the room increases to 20°C?

Only one answer is correct among these 4 choices:
- Cold air molecules collide to generate heat energy.
- Cold energy in the room transforms into heat energy.
- The room becomes warmer as heat energy is added to the room.
- The room becomes warmer as cold energy is pushed out of the room.

Could you tell me which one is correct?

The room becomes warmer as heat energy is added to the room.