Why do hot air balloons only go to high?

Question

What keeps them from drifting off into outer-space?

It should be getting colder as it goes up, & the balloon is farther away from earth. The further an object is from earth, the less the gravitational pull is, right? So it should be easier & easier to break free of the pull of gravity as the balloons go up.

What keeps them from going up forever, or until their hot air supply runs out?

Answer 1

There is a gravitational potential barrier (GMm/R) which the hot air balloon has to break in order to get into the space i.e., the balloon should have a kinetic energy > potential barrier and it is the escape velocity which gives it the necessary kinetic energy.
(1/2)mv.v = GMm/R
v=sq. root (2GM/R) ----escape velocity--independent of mass of the object.
This keeps them from going to outer space.

Answer 2

Yes it is true that farther away from the earth the less gravitational pull but the pull is not strong enough to affect the ballon or anyother object in earth's orbit. Also a hot air ballon only has a limited air supply and as the air thins the ballon should no longer increase in height (i think thats true).

Answer 3

They go 'up' for the same reason that boats float. They displace a greater mass of air than their mass. But, as you go further up, the air density becomes lower and so the lower density air in the balloon gets closer to the density of the surrounding air. At the point the densities are equal, there is no more buoyant force and the balloon quits rising.

HTH ☺


Doug

Answer 4

hot air created by the burner create gas to expand, and it gives lighter air than the out side air. that the rule higher temp= more gas expands, and lighter it gets= goes up