1. AN EXPANDING SITUATION

2. Get Started What happens when air is heated? Can you see hot air?
What happens when air is cooled? Can you see cold air?

3. Work On It

4. Communicate
Based on your observations and our discussion from the Expanding Situation experiment, answer the Communicate questions on page 7

5. Build on What You Know
Explain in your flight passport how you got your balloon to rise high enough to clear the hill

6. A key concept to the study of air and flight is that air expands when heated and contracts when cooled. This characteristic is important to an understanding of how lift works. As air is heated, the molecules speed up and move farther apart. This heated air takes up more space…

7. As the air is cooled, the molecules slow down and move closer together, causing the air to take up less space. Heated air, which has greater volume than cooler air with the same mass, will naturally rise, since the pull of gravity works harder on the denser air.