The Breakdown: Urban Obstacle Courses

If you saw the most recent James Bond movie, Casino Royale, you might recognize the sport of parkour. It involves amazingly acrobatic, spontaneous physical feats, often performed in an urban setting. And although it looks like it's straight out of the superhuman stuff of The Matrix or Spiderman, it is very real. Its practitioners leap from rooftop to rooftop, scale walls and backflip over obstacles.

Watching a clip like this one, it's tempting to think there's some deft camera work at play, or some skilled CGI action, but these people are really just taking advantage of basic physics. They're taught to respect the laws of motion: They often roll when landing on a hard surface to reduce the impact on their legs and back. They take advantage of momentum, too, using body movements to transfer horizontal force into vertical when switching from running towards to scaling a wall. Similarly, they kick off walls to get a little higher and perhaps reach a ledge they couldn't have grabbed with a straight jump. Naturally, physics also gets them back now and then. Though you're not likely to catch too many slip-ups on the popular web videos or TV commercials featuring parkour and its variations, these guys are human: Friction and gravity don't always cooperate, and they do fall now and then.—Gregory Mone