In 2009 Jamaican sprinter Usain Bolt set the world record in the 100-meter sprint at 9.58 seconds. For those of us more accustomed to sitting than sprinting, to translate this feat into terms of speed is to simply underscore the stunning nature of Bolt’s performance.

Speed is the rate at which an object (or person) moves through time. It is represented mathematically as speed = *d/t* (in which *d* is distance and *t* is time). That means that Bolt’s speed during his world-record run was 10.44 meters per second. Since many people are more familiar with automobiles and speed limits, **it might be more useful to think of this in terms of kilometers per hour or miles per hour: 37.58 or 23.35, respectively**. That’s faster than the estimated average traffic speed for the U.S. cities of Boston, New York City, and San Francisco. Even more astounding is the fact that Bolt started from a speed of zero and then had to accelerate, which means that his top speed actually was faster.