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Oct15-09, 08:40 PM   #10
 
Recognitions:
Science Advisor Science Advisor
I think I should point out that the drag force (which is what the ball experiences from the fan) is not a conservative force. The energy associated with aerodynamic drag (or viscous effects in general) is dissipative. Energy is still conserved- the total energy is *always* conserved- but some of the energy is dissipated and not available to be converted back into work.