Some of the best recent Flash games have been those that have stuck rigidly to the laws of physics. Roller Coaster is a good example of that. In fact, it's been produced by Cambridge University as a cross between a simulation and a game.

You start with an incline, and the aim on each level is to move the supports up and down to create the curve of a roller coaster track. You need to strike a balance between providing maximum enjoyment and not making your riders ill.

It's all done with g-forces: they need to be high enough that the riders aren't bored, but make the curves too steep and you'll injure or even kill the rider.