Hot Air Balloon and Buoyancy

[Schwann]

Ok so here it goes. Hot air rises because it has more kinetic energy, more spread out, and thus less dense. In a hot air balloon the less dense hot air allows the balloon to float in an atmosphere of colder, more dense air. Is this correct.

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[BerkReviewTeach]

Ok so here it goes. Hot air rises because it has more kinetic energy, more spread out, and thus less dense. In a hot air balloon the less dense hot air allows the balloon to float in an atmosphere of colder, more dense air. Is this correct.

Yes!

If the weight of displaced cold air (which defines the buoyant force) is slightly more than the weight of the hot air in the balloon and the balloon system itself, then the balloon will lift off of the ground. As the balloon lifts, the surrounding air gets colder, so there is an increasing acceleration upwards. The hot air balloon must be vented and/or cooled in order to get it to stop ascending. Once it is hovering, the buoyant force up = the weight of the balloon, basket, contents, and hot air.

 

[nothing123]

Ok so here it goes. Hot air rises because it has more kinetic energy, more spread out, and thus less dense. In a hot air balloon the less dense hot air allows the balloon to float in an atmosphere of colder, more dense air. Is this correct.

Essentially yes, although I don't know if it's so much they are heating air or simply utilizing some form of lighter "air" (i.e. more helium based). At any rate, the gas in the balloon does have to be less dense than the air it's displacing in order for the buoyant force to exceed its own weight.

 

[BerkReviewTeach]

Essentially yes, although I don't know if it's so much they are heating air or simply utilizing some form of lighter "air" (i.e. more helium based). At any rate, the gas in the balloon does have to be less dense than the air it's displacing in order for the buoyant force to exceed its own weight.

Great point about lighter than air systems. They are generally closed systems and function much like submarines in the air. "Derigibles" used to be a common MCAT topic a few years back and they emphasized the difference between open hot-air balloons versus closed helium derigibles.