Flipping out

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At the 2006 X Games, Travis Pastrana became the first motocross rider to launch his dirt bike into a successful double backflip. The record-breaking stunt made James Riordon, a physicist with the American Physical Society in Maryland, wonder if more flips were physically possible.

After performing some calculations, Riordon concluded that the amount of kinetic energy, or energy of motion, a rider has when he or she flies off the ramp is enough to complete a maximum of four backflips.

But don't try this at home! To land a quad backflip, equal amounts of energy must go toward gaining air and rotating backward. If a rider is even result could be disastrous. Jump too high, and there won't be enough energy to spin. Jump too low, and the biker gains spinning power, but won't have enough time to make it four times around.

So how long before a pro rider sticks a triple? "It's not a question of physics stopping them from three flips; it's a question of nerve," says Riordon

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