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Old 01-29-2013, 07:04 PM   #27 (permalink)
mort
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Quote:
Originally Posted by darcane View Post
This is incorrect. Your version of physics would make setting land speed records trivially easy.
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So, if you accelerate at 1g at 50mph and it takes 80hp (20hp due to aero drag, 60hp you accelerate your mass at 1g, ignoring rolling resistance), at 100mph you should require 220hp (160hp due to aero drag, 60hp to accelerate your mass at 1g).
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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