If a hot air balloon is being carried by a continuous wind current in a particular direction, in which direction will the flags on its basket wave?


1 Answer 1


The balloon will asymptotically approach the wind velocity. As it gets close, the force due to drag will decrease because the apparent wind will be small. To the extent it matches the wind velocity, flags will hang straight down. To the extent it is (barely) below wind velocity, the flags will point (just a little) in the direction of the wind. If the wind slows down a bit, the flags will point backwards until the balloon slows down to the new velocity.

  • $\begingroup$ Concise and correct. I particularly like the last statement - a counterintuitive twist. $\endgroup$
    – Floris
    Jan 16, 2016 at 16:00
  • $\begingroup$ Since the wind is moving the balloon and given the size of hot air balloons can the speed of the balloon reach that of the wind? $\endgroup$
    – ispirato
    Jan 18, 2016 at 7:00
  • $\begingroup$ @ispirato: I said it in the first sentence. The balloon speed will approach the air speed asymptotically. It is the same as if the balloon were magically started moving at the wind velocity in still air. It will slow down, appoaching zero speed asymptotically. The two situations are equivalent-the balloon starts with a certain velocity relative to the air and that velocity decays away. $\endgroup$ Jan 18, 2016 at 7:03

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