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#21
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Galileo To Taste Jupiter Before Taking Final Plunge
In article ,
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! | |
#22
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Galileo To Taste Jupiter Before Taking Final Plunge
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