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ORIGINAL: mik_ok
Sorry - I meant to say power requirement varies with the cube of speed. You're correcu in that drag varies with the square (= 0.5 x CdA x air density x speed squared)
but power requirement is proportional to both drag and speed (can't remember that equation off the top of my head [] ) so power requirement does indeed increase with the cube of velocity. [8D]
Quite right. Drag force is proportional to speed squared, so power required to maintain that speed is proportional to velocity cubed.
Energy = Force * Distance
Power = Energy / Time
Speed = Distance / Time
=> Power = Force * Distance / Time = Force * Speed.
(which we know from the torque - power relationship in any case).
Wheel torque has to be proportional to speed squared, so power has to be proportional to speed cubed. That model gives good looking numbers in any case - 200 mph cars generally need at least 450 bhp, more if they sacrifice some Cd for downforce.
Tom
