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Just slip out the back, Jack, make a new plan, Stan
Don't need to be coy, Roy, just listen to me
Hop on the bus, Gus, don't need to discuss much
Just drop off the key, Lee, and get yourself free
The C6 don't have a key lee. Push button start bart...
Location: West Los Angeles and Rancho Palos Verdes
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When I began this thread, I was asking in regards to most cars. Some people have unusually fast cars with unusual characteristics, but I wasn't asking about those types of cars, which I assumed would be implicit at the beginning of this thread..
Thanks to everybody who addressed my original post.
Simple physics. E =1/2m(v**2). Energy increases by the SQUARE of the speed. It takes four times as much energy to go at twice the speed. If I've lost you since you never had physics in HS, I apologize.
At those speeds, wind resistance doesn't play much of a factor, it's primarily gearing.
No. Wind resistance increases as the square of velocity. A car has an awful lot of aerodynamic drag at 60 mph. You'll notice it more in a car with a lousy drag coefficient. A brick on wheels like a full size SUV/pickup will be impacted more than a slippery egg-shaped design sedan.
Engines have their peak power at some RPM. 6,000-ish RPM for many cars. At 6,000 RPM, you get better acceleration going from 10 mph to 20 mph than from 60 mph to 70 mph. Even with a lousy slush-o-matic, you can put your foot to the floor and get the RPM up to red line at 60 mph.
The power available from an internal-combustion engine (or an electric motor, or a rocket, or really anything other than a Brayton-cycle engine) is basically constant with speed. So for a given Hp, there's less propulsive force available as vehicle speed increases.
And, Force = Mass * acceleration.
So as the available force decreases (with, recalling the above, increasing speed), the acceleration all also decrease, assuming that the vehicle mass is constant. This will be true regardless of aerodynamic drag. if one were to drive an electric car on teh surface of the moon, one would also find, that acceleration attenuates as the vehicle speed increases.
No. Wind resistance increases as the square of velocity. A car has an awful lot of aerodynamic drag at 60 mph. You'll notice it more in a car with a lousy drag coefficient. A brick on wheels like a full size SUV/pickup will be impacted more than a slippery egg-shaped design sedan.
Engines have their peak power at some RPM. 6,000-ish RPM for many cars. At 6,000 RPM, you get better acceleration going from 10 mph to 20 mph than from 60 mph to 70 mph. Even with a lousy slush-o-matic, you can put your foot to the floor and get the RPM up to red line at 60 mph.
Since p, Cd, and A are all constants you're left with v^2.
I guess if 400 and 3,600 is a negligible difference to you, then it's a negligible difference.
That's really a stupid thing to say though. It's a bigger difference than 60 versus 120. Why don't we get fabulous mileage at 20 then? Because the drag at 20 mph in a car is a negligible. By 60 mph that's no longer true. That 900% increase in aerodynamic drag from 20 to 60 has become important in terms of fuel economy. That's why you'll get better gas mileage going 50 than 60 or 60 instead of 70.
The transmission multiplies the torque, at the wheels, most in the lowest gear. A speed increases the trans must shift up to higher gear ratios, producing less torque multiplcation, to keep the engine rpm in an acceptable range.
Maybe on the Moon it is negligible, but here on Earth where most of us drive it is a huge factor.
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