Can a Penny Dropped From a Building Kill a Pedestrian Below?

May 3, 2007 — -- Have you heard this one? That a penny thrown off the top of the Empire State Building could kill a pedestrian below? Or that it would go through the sidewalk?

Many visitors outside of the famous skyscraper we spoke to had heard all about killer pennies. "Anybody who gets hit by that penny is about to die, 'cause that's a long way for a penny to fall," said one young man. "It could actually go through someone's skull," said another.

Tourists at America's tallest building, the Sears Tower in Chicago, agreed. "If it hit concrete it would probably be smashed into little bits, or just flattened out if it landed sideways," said one man.

"I think it would go through the roof of a car, sink into the cement, or hurt someone," said one woman. "Not a pleasant thought. Don't want to try it, but it would be kind of interesting to find out," she said.

We thought so too, so we asked University of Virginia physics professor Louis Bloomfield about it. "They're thinking of a world without air ... but air resistance is a big deal for little things. It slows down leaves, it slows down raindrops and it slows down pennies," he said.

"The penny is heavier [than a raindrop] but it flutters as it comes down. It's very unstable in the air."

Bloomfield has heard about the myth so often he tackles it in his latest book, "How Everything Works."

"Pennies, they're not aerodynamically stable ... they catch a lot of wind ... basically they're safe," he said.

Safe? Really? We wanted proof. "The ideal thing would be to drop a penny off the Empire State Building and catch it," he said. "But sadly, no building will let us do this because they're all worried about the myth!"

The Test

At our request, Bloomfield concocted another test. He filled a large weather balloon with helium and attached a penny dispenser to it that spits out pennies one at a time. He launched the balloon hundreds of feet into the air and then a remote control device released the pennies and he ran around trying to catch them.

He didn't actually catch any of the pennies, but was hit by several of them, one time on the chin. "It was like getting hit by a bug ... it was noticeable, but nothing more. I was just disappointed I hadn't caught the thing," he said. "I didn't catch it because I'm a bad catcher and it was a windy day, but basically these things are just fluttering down."

But his balloon only went up a couple hundred feet -- the Empire State Building is over a thousand feet tall! "Even though we didn't go as high as the Empire State Building, it doesn't matter. The penny will hit full speed after 50 feet or so, and it just coasts," he replied.

The pennies "reach terminal velocity and no matter how high we put the balloon, they never picked up any more speed." Terminal velocity is the maximum speed a falling object reaches and is determined by the object's weight and air resistance. Because a penny is lightweight and not aerodynamic, air resistance slows it down so much that its terminal velocity is quite slow.

But not so for many other objects, Bloomfield warns. "Even if they're relatively small, if they're aerodynamically streamlined -- like a ball point pen -- they'll reach the point at which they're going a couple hundred miles an hour, and that's dangerous," he said. "Don't dump your handbag out the top of a building. Something in that bag is likely to go awfully fast."