Go through this NOVA site and then
summarize the key points
learned:
✄ When the pilot turns on the burner of a hot air balloon, balloon begins rising upwards. It will not float until the ropes holding it down are untied though. The heated air now contains particles that are starting to move around more and more and will be starting to interact with one another. Soon enough they will start moving faster and faster.
✄ The particles begin to move much faster and farther away from one another, as constant heat is being applied. The particles are moving so fast that some of them escape from the opening in the bottom of the envelope. With all these air particles escaping from the balloon, the density has now decreased from its
original density. However, it has a constant volume.
✄ When the pilot of the balloon wants to drop and land, he/she turns off the burner, and the air particles begin to move closer together. Doing this brings in particles from the atmosphere to naturally avoid creating a
vacuum.
✄ The particles begin to move much faster and farther away from one another, as constant heat is being applied. The particles are moving so fast that some of them escape from the opening in the bottom of the envelope. With all these air particles escaping from the balloon, the density has now decreased from its
original density. However, it has a constant volume.
✄ When the pilot of the balloon wants to drop and land, he/she turns off the burner, and the air particles begin to move closer together. Doing this brings in particles from the atmosphere to naturally avoid creating a
vacuum.
Sources:
✿ http://www.pbs.org/wgbh/nova/balloon/science/density/shape.html
✿ http://upload.wikimedia.org/wikipedia/commons/c/cf/Colorado_Springs_Hot_Air_Balloon_Competition.jpg