Quote:
Originally Posted by mort
Hi darcane,
My physics is fine. You misunderstood the point of my post.
Yes, the power going to aerodynamic drag grows as the cube of the speed. But what you wrote (above) is wrong regarding acceleration.
Power is force multiplied by speed.
So if it takes 60 hp at 50 mph to accelerate at 1 g, then at 100 mph the power needed to accelerate at 1 g is 120 hp.
My point was that the reason you feel less oomph at high speed than at low speed is that if you only have the same amount of power - that power buys less acceleration the faster you go.
If you are going really fast, then aerodynamic drag uses up all your power, and you can't accelerate. But at relatively slow speeds, where the power to overcome rolling resistance and aero drag are low, then most of your power is available to accelerate. Consider if you could apply full power at 5 mph compared to 25 mph. If the power at the tires is the same then your acceleration at 25 mph will be 1/5th what it was at 5 mph. This why it is easy to burn rubber from a stop and impossible at 40 mph.
The actual physics: P = V * M * A
-mort
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Bugger, I believe you are mostly right on this. I had a free-body diagram in my head to determine what forces would be acting on an accelerating car to account for everything. While the force would be the same in either case to get 1g acceleration (after subtracting the effects of aero and friction) the power would not, but would instead be proportional to velocity as you state.
However, your example is still misleading because the effects of aerodynamic drag increase exponentially and very quickly dwarf the power needed for acceleration.