From: henry@spsystems.net   
      
   In article <3f78089c$0$58702$e4fe514c@news.xs4all.nl>,   
   Wim Dekker  wrote:   
   >I don't understand why kinetic energy increases quadratically   
   >with speed while the energy it costs to increase speed itself   
   >seams to be directly proportional to the speed.   
      
   Assuming that that last phrase should have been "to the speed increase",   
   no, it's not.  The energy cost is what you'd expect from the quadratic   
   increase in total energy with speed -- the energy increment required for a   
   speed increment rises with the absolute speed as well as with the size of   
   the speed increment.   
      
   You have to be very careful to do your bookkeeping consistently, and to   
   use the same frame of reference throughout.  You cannot measure total   
   energy with respect to the ground, and energy increment with respect to   
   the vehicle!   
      
   The rate of energy consumption of a rocket engine looks constant only when   
   measured with respect to the vehicle.  When all measurements are done with   
   respect to the ground, much of the energy invested in accelerating the   
   vehicle early on -- when its tanks are nearly full -- goes into making the   
   fuel more energetic, providing the rocket engine with much higher energy   
   later in flight.   
      
   For a rocket, it is usually much more useful to think in terms of momentum   
   than in terms of energy.   
   --   
   MOST launched 1015 EDT 30 June, separated 1046,         | Henry Spencer   
   first ground-station pass 1651, all nominal!            | henry@spsystems.net   
      
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