From: vitalmis@optusnet.com.au   
      
   Ian Stirling wrote:   
      
   > Keith Harwood  wrote:   
      
   >> The only time it's not stationary in the airmass is when something is   
   >> dragging on the ground (as at launch or landing) or when it is passing   
   >> through a windshear.   
   >   
   > Or when wind direction changes.   
      
   Yup, but it's only momentary. The force arising from the wind change is   
   applied over the whole crosssection of the ballon and is enormous compared   
   to the mass of the balloon. From F=ma, the acceleration a must be very   
   large. If the change in velocity of the wind is v then the time t to change   
   the velocity of the balloon is given by v=at. v is small, a is enormous, t   
   is terribly small. But the rate of change of the wind isn't all that crash   
   hot, so if t is terribly small then v must be terribly small. If you do   
   this properly using the rate of change of wind velocity to calculate F   
   you'll find that to all intents and purposes the balloon is embedded in the   
   air mass regardless of changes in the wind.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)