As you watch high jumpers sail over the bar this summer at the London Olympic Games, keep this equation in mind: U2 = 2gH. It explains why most of jumpers do the backward flip known as the Fosbury Flop. As University of Cambridge mathematician John Barrow writes in his book Mathletics: A Scientist Explains 100 Amazing Things about the World of Sports (W. W. Norton, 2012), the Fosbury Flop keeps one’s center of gravity low to the ground, and the lower one’s center of gravity, the less energy is required to successfully jump over the bar. In the above equation, U is the speed of the jumper (and thus the energy required), g is the acceleration caused by gravity, and H is the height of the center of gravity. Surprisingly, it is possible for the high jumper’s body to fly over the bar while his or her center of gravity passes below it.
Now, you might ask, why do many of the jumpers leap backward? That part is easy: when your back is to the pole, there is less chance that your arms or legs will hit the bar and knock it down.
COMMENT AT ScientificAmerican.com/aug2012
This article was originally published with the title "Fact Finder: High-Jump Physics"