What is acceleration for? It doesn't seem to be affecting the speed.
edit: Anybody remember the name for that effect where the frequency modulations interfere with each other to create illusionary effects (the one where when you get the RPMs of a wheel up to a certain value, it will momentarily appear as if its spinning in the opposite direction), yeah I'm having fun with that effect right now :P
Acceleration - it affects the rate the speed increases. It ranges from -1000 to +1000 and that's mph per second. The speed is in mph. The default is 20 which is close to Earth's gravity. Try setting the acceleration to 1000 or something and you'll go from 0 to 1000 mph in one second and the speed increases by 16.666... mph each frame.
I don't remember what the effect is called though, but it's one of my favorites.
The wagon wheel effect?
Pulled that one out of my hat there. ;) Ah, curious psychology...
Hmm. That article doesn't have any images related to it and I happen to have an animated GIF (though rather small) that demonstrates the effect. I should add it to the article.