Falling Man

Professor Kakalios cites a classic Spider-Man episode to explain what happens when a body in motion stops too soon. When the villain pushes the superhero's girlfriend, Gwen Stacy, off a bridge, Spider-Man caught her in his web. But her neck snapped and she died.

"That's one of the times that comic books got it right," said Kakalios, the author of "The Physics of Superheroes." "The force of the webbing was so great that her body could not handle it. Anytime something stops so abruptly, there's going to be great trauma on the body." In the comic, Gwen went from at least 95mph to zero in a split second--which means that Spider-Man was responsible for the death. He should have figured out a way to use his web to slow her descent before catching her. Reducing the deceleration--the rate at which an object comes to a stop--is critical to safety in high-speed vehicles like cars, spaceships, and even roller coasters.

If the platform Moreno clung to hit something on the way--like the side of the building--its momentum could have slowed. In effect, Moreno would have experienced several discrete falls rather than one single fall.

That's how car safety equipment works. First the seatbelt stops the body's forward movement, with four inches of slack to allow the body to continue to move forward without slamming into the dashboard. The airbag then deploys, slowing the body's movement, providing a soft impact area and distributing the crash's force over a large area.

(Studies of falls have been important in the development of safety equipment. A 1942 study of falls from dangerous heights was used by Ralph Nader as part in his analysis of auto dangers in his 1965 book "Unsafe at Any Speed.")

Another factor may have come into play; it's possible that the wind currents flowing through New York's forest of buildings created some kind of cross-pressure that also slowed the plunge. As any sailor in cities like Boston and Chicago can attest, the movement of wind through buildings can create heavy and erratic gusts.