Quote:
Originally Posted by Matthew Shea  Even in a vacuum, as in outer space, the speed you're moving at is proportional to the square of the energy used. In other words, if you're traveling twice as fast, it requires four times the amount of energy to move a given mass. |
In fact I buggered it up. a=f/m, the relationship between acceleration and force or energy is linear, not exponential.
To accelerate to twice the speed will take twice the energy, but in a vacuum maintaining that velocity requires no energy (discounting the micro impacts of space dust and debris)
Now take wind resistance into the equation
p=1/2*pv(cubed)AC
power is half the density of the fluid by velocity cubed by area by drag coefficient.
to drive twice as fast will use 8 times as much fuel to push the car through that air (ignoring engine and gearing inefficiencies) so it will be 4 times as much fuel per distance travelled.
The efficiencies in the gearing, engine and drivetrain of a car seem to dictate the fuel efficiency at speed. I guess a car is at its most efficient in top gear at revs where there is the most power at partial throttle.