Quote:
Originally Posted by Maury Markowitz
Steady state gas milage is roughly due to two factors, the air resistance which goes with the square of speed, and rolling resistance which goes with the speed. So, roughly, milage is the fuel use at idle dividend by the cube of speed. Roughly. Then you add in things like hills and such.
The part I don't understand is acceleration. It would *appear* that the amount of energy needed to accelerate to a given speed is a fixed, it's simply 1/2*m*v^2. There's no "t" term in there for the time you take, nor an "a" for the acceleration. It's just initial vs. final velocity.
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first, the wind resistance is cube of speed, but you get to divide by miles covered, so your MILEAGE is a function of speed squared.
Mileage and acceleration are indeed sort of unrelated, but they do tie together.
The faster you accelerate, the more time you spend at "top speed", which means you burn more fuel simply because you are going faster.
Second, the ECU computer in the car richens the mixture drastically above a certain point. It goes "open loop" and throws gas at the engine, because extra gasoline gives more power. You REALLY want to stay out of "open loop" for mileage.
Third, an automatic transmission will stay in low gears longer, meaning more average RPM's, which means more gasoline burned.
Fourth, driving conditions can mean you burn more gas as a systems point of view. If you and I are next to each other, and the light turns green, and you rabbit out there and get up to 45mph , only to stop 1/4 mile on for the next red light, and I ease out, and my top speed is only 30 mph, you burned well over twice as much gasoline on that single section of road than I did. First, you accelerated to 45 which takes twice as much gas as it takes to accelerate at 30mph, and second, you spent time at 45 mph which burns twice as much gas as it does for 30mph if you look at only wind resistance.
Hope this helps
and yes, i'm also a math/physics major.