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It has nothing to due with "convection" or any other motion of the air. (If it did, then how would you explain floating helium balloons, which are at the same temperature as the air?)

The pressure of the air around you (even perfectly still air) decreases with altitude. It's well known, for example, that the air pressure at the top of a mountain is much less than at the mountain's base--that's why you need breathing equipment up there. The difference is caused by the weight of the air itself--lower locations have a greater mass of air weighing down on them than higher locations, and that produces pressure.

Even within a room, there's a SLIGHT difference in air pressure between the floor and the ceiling. The air pressure at the floor is slightly greater. That difference produces a small upward force called "buoyancy" on EVERY object in the room, including you. Air pressure pushes on you from all directions; but the pressure on your feet (pushing up) is slightly greater than the pressure on your head (pushing down). This isn't enough to make you float, but it is enough to reduce your measured weight by a small amount.

The amount of buoyancy acting on an object depends on an object's VOLUME. For a typical adult human (in typical air), the buoyant force on their body is around 3 ounces. That means the number you see on the bathroom scale is about 3 ounces less than your "real" weight.

It also means that if your "real" weight (due to gravity's pull) were less than 3 ounces, the buoyant force would overcome gravity, and you would float away! So the trick to floating is to reduce your weight (your mass), while increasing your volume (to increase the buoyant force). Both of those actions decrease your density. It turns out that if you decrease your density to the point that you're less dense than the air around you, the buoyant force will exceed the gravitational pull, and you'll float.

So that's what hot air balloons do. Hot air is less dense (has fewer molecules per cubic meter) than cold air, so that reduces the balloon's weight. But because those molecules are moving fast, they have enough pressure to expand the balloon, increasing its volume (and hence increasing the buoyant force). When the buoyant force exceeds the weight, the balloon rises.

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13y ago

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Related Questions

Is a hot air balloon a balanced or unbalanced force?

A hot air balloon is balanced because the upward lift force from the hot air inside the balloon is equal and opposite to the downward force of gravity on the balloon and its contents. This balance allows the hot air balloon to float in the air.


What is the buoyant force of a hot air balloon?

The buoyant force on a hot air balloon is equal to the weight of the air displaced by the balloon. When the air inside the balloon is heated, it becomes less dense than the surrounding air, causing the balloon to rise. The buoyant force allows the balloon to float in the air.


What force brings a hot air balloon to earth after the hot air is let out?

Erm.. no.. i believe its Buoyancy... this force causes u the hot air balloon to rise.. not Gravity..


What force makes a hot air balloon rise up into the air?

The upthrust exerted by surrounding air on the balloon.


What keeps a hot air balloon aloft?

Hot air is lighter. See the related link.


What happens when the force acting on a hot air balloon are balanced?

When the force acting on a hot air balloon is balanced, the balloon will remain at a constant altitude. This means that the buoyant force on the balloon is equal to the gravitational force acting on it. As a result, the balloon neither rises nor descends.


Does gravity affect a hot air balloon?

Yes. Without gravity, a hot air balloon would rise infinitely. You could never return to the ground. Balloons tend to hover more or less. The force of the air pushing up on the balloon and the force of gravity pulling down on the balloon are usually very close to one another. This keeps the balloon at a steady height, unless you heat the air in the balloon, or let it cool.


What are the two forces that affect a hot air balloon?

The two forces that affect a hot air balloon are buoyancy and gravity. Buoyancy is the force that lifts the balloon due to the difference in densities between the hot air inside the balloon and the cooler air outside. Gravity acts to pull the balloon back down toward the ground.


How does hot air balloon work?

the balloon works with the poplo force forcing it up


What force brings the balloon to earth after the hot air is let out?

Force of gravity


What forces are used in a hot air balloon?

In a hot air balloon, buoyant force (lifting the balloon due to the density difference between the hot air inside the balloon and the cooler air outside) and wind force (pushing the balloon in a particular direction) are the primary forces involved in its movement. Additionally, the pilot can control the vertical movement using the burner to heat the air inside the balloon.


What force keeps a hot air balloon up in the air?

It is because hot air is lighter than cool air. Because it has less mass per volume unit, the hot air needs to be propelled upwards into the fabric using the burner. To lift 1000 pounds of weight, you'll need about 65000 cubic feet of heated air. They simply float with the wind and are not directed, until the pilot lands the balloon.