Throckmorton
Lifer
- Aug 23, 2007
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Originally posted by: jagec
Originally posted by: Throckmorton
Originally posted by: KillerCharlie
That is incorrect. The force required to propel the vehicle is essentially just the drag plus the rolling resistance from the tires. These two forces are typically in the same ballpark.
The rolling resistance roughly estimated as vehicle weight times rolling coefficient. The rolling coefficient on a typical car is 0.015 - the force is 1.5% of the vehicle weight. On a 3000 pound car, that's 45 pounds.
Drag, usually written as drag coefficient times reference area times dynamic pressure, is usually the same order of magnitude. For the Corvette, the CD*A is about 6.5. The dynamic pressure at 60 mph is about 9.2 psf. That means the drag is about 60 lbs.
In fact, in many cases, semi-trucks have a lot more rolling resistance than drag - meaning that drag on your car is a bigger part of performance than it is for a semi.
One interesting thing the drag does is make the vehicle's performance highly dependent on weight. If there was no drag, your car's acceleration would be almost completely independent of weight.
No, if there was no drag, acceleration would still depend on the ability of the drivetrain to accelerate the mass, which is the biggest factor in acceleration as it is. If there was no drag, it would take no energy to maintain the momentum of a car, so you could go infinite distances without using energy like you would in space.
Acceleration is and always will be F=ma...fully dependent on weight. Drag comes into play by reducing the available surplus force the engine is generating...it takes a certain amount of power just to keep the car going at a given speed, and that increases with speed, reducing your acceleration. If you had frictionless bearings and were driving in a vacuum, your acceleration would be constant...or at least, if you had an infinitely variable transmission...and no weight loss from fuel consumption...and a supply of air to burn it...well, let's just say it won't be happening anytime soon.
Yeah but he said that without drag, acceleration would be independent of weight, which makes no sense. Weight is the biggest factor until you get to high speed, and without drag it would be the only factor.