I don't agree with sacicons about this part, because that would mean if you sat in your driveway with car in nuetral, gunned it, watched the revs go up, your gas gauge should also go up since the alternator would be sending more current.

There is a voltage regulator in cars so that the voltage does not exceed a specified amount. I have never seen a car where the gas gauge goes up as you rev high while the car is stopped.

I do agree with the part that includes movement from the car (as in hard right corner) moving the gas gauge. There is a float in your gas tank that monitors the amount and sends that signal. If you make any long sudden moves with your car, it will affect the reading. You'll notice sometimes if you're gunnin it for a bit, or braking for more than a few seconds, the gauge will move (especially noticable while the tank has less than a quarter in it).