Statement 1-- A balloon filled with helium doesn't rise indefinitely.
Statement 2--The balloon halts at such a height where the weight of the air displaced is just equal to the weight of the helium gas and the balloon.

Question

Statement 1-- A balloon filled with helium doesn't rise indefinitely.
Statement 2--The balloon halts at such a height where the weight of the air displaced is just equal to the weight of the helium gas and the balloon.

anonymous · Answer

The answer is :--statements 1 and 2 are true and that statement 2 is the correct explanation of 1.
NOW MY QUESTIONS:
1.Why don't we consider drag(viscous) force here? Or do we?
2. How will the balloon halt when the weight of the air displaced is just equal to the weight of the helium gas and the balloon? AT THIS POINT, the net force should be 0 and it should rise to a higher height before coming down, and then execute some sort of periodic motion up and down.

anonymous · Answer

@Vincent-Lyon.Fr

vincent-lyon.fr · Answer

The air drag, which is not mentioned here, is the force that explains why the balloon does not oscillate about its equilibrium altitude.

Whether it is present or not, it depends on velocity, and so is zero when the balloon is at equilibrium. This is why this altitude can be worked out without any reference or knowledge with respect to air drag.