when an air balloon rises, what happens to the balloon that allows it to float?

Question

What component of density changes?

A. Would the density increase or decrease?

B.Explain hhow the ballon would rise higher and faster during the morning or afternoon flight?

C. as you rise higher and higher, and faster, why would you need to increase the heat in order to keep the balloon aloft?Whast thins out as you go higher?
oh and this has nothing to do with lower temps in the upper atmosphere.

Thanks !

Answer 1

Hot air is less dense than cold air. Work from there.

Answer 2

The point of this question is that at ground level the air inside a hot-air balloon is more dense than the air a few hundred feet up -- yet the balloon can rise to that height and beyond.

What component of density changes?
It depends on the design of the balloon. In the simplest scenario, where the balloon is completely enclosed, the volume changes. It's still the same mass of air, but the balloon expands. If the balloon has a fixed volume, with a vent at the top, then it's the mass that changes. I think the former design is used for helium weather balloons and the latter for hot-air recreational balloons.

A. The density decreases, either way.

B. In the morning the air is cooler and thus denser.
Suppose a fixed temperature difference deltaT between the inside of the balloon and the outside. For the air displaced by the balloon, PV = nRT; for the air in the balloon PV = xR(T + deltaT). Lift = k(n - x), where k is the average molecular weight of the air.

nRT = xR(T + deltaT)

cancel the Rs, and divide b T

n = x (T + deltaT)/T

Lift = k x(1 - (T + deltaT)/T)

simplify

Lift = kx*deltaT/T

So lift is inversely proportional to temperature. There would be more lift in the cool of the morning than in the heat of the afternoon.

C uses similar reasoning, only with a decrease in P. For a fixed deltaT, lift is proportional to P, because both n and x are.

Answer 3

when air ballon rises,the gaseous or the heat of the gaseous give the ballon to rise.actually,when something like ballon is floating the density is low than the density of air up there.for number two,i would like to say the pressure in morning-approach-to-noon and noon is lower.however you need to that the pressure at the base of sea is higher than the pressure in the air up there.ok....for number three,the higher the heat or the temperature,the higher the pressure is produced.so the ballon will keep aloft.(in science the term heat and temperature are different thing)