Could A Penny Dropped From The Empire State Building Actually Kill Someone?

In July, two Russian climbers scaled the Empire State Building as a publicity stunt — and to secure an epic proposal spot. Fortunately, the risk-taking lovers made it back to the ground safely. Once the tallest building in the world, the Empire State Building measures 1,454 feet from base to pinnacle. Its towering stature has birthed many myths and legends, including tales of ghostly seances and haunted empty floors. Perhaps the most enduring legend, however, is that of the deadly penny drop, which claims that a penny dropped from the top of the Empire State Building can gain enough speed to kill someone once it reaches the ground.

As with most myths, this one is based in some truth, though it reaches an incorrect conclusion. It's true that a free-falling penny can reach surprisingly high speeds, but they're not speeds that will do any damage. Because pennies are flat, light, and round, they inevitably flip and tumble through the air, even in the absence of wind currents. Air particles collide with the tumbling disc, pushing it with an upwards force. Once the upward force of air resistance matches the downward force of gravity, the penny stops accelerating and reaches a terminal velocity of around 50 mph within the first few seconds of its fall. The same phenomenon also explains why a car's fuel economy tanks around 75 mph.

It requires a minimum of 68 joules of kinetic energy to fracture a human skull. A 2.5-gram U.S. penny traveling at 50 mph produces about 0.2 joules of kinetic energy. That's not even close to being deadly. Getting hit in the head by a penny dropped from the Empire State Building would probably feel like a sharp flick or a heavy raindrop, and you might not even notice it if you're wearing a hat.

Thanks to air resistance, it would be impossible for a penny dropped from the Empire State Building to kill someone. And even if you remove air resistance from the equation, a 2.5-gram penny would only reach about 200 mph when dropped from the 1,454-foot height of the Empire State Building, creating far fewer than the 68 joules of energy needed to split a skull. So how fast would a penny have to travel to become deadly? Thanks to some math from Isaac Newton, physics has the answer to this hypothetical question. 

Given the 2.5-gram weight of a penny, it would need to travel approximately 521 mph, to produce 68 joules of energy. At such a speed, a penny would penetrate the skin, and it could even fracture the cranium. Any faster, and the chances of survival plummet as the penny reaches supersonic speeds. 

Of course, such scenarios are entirely hypothetical. Here on Earth, air resistance slows down everything that moves within our atmosphere, including the most aerodynamically-optimized shapes, such as bullets and rockets. (In fact, if you shot a bullet in the vacuum of space, it would just keep flying.) Fortunately for the folks visiting the Empire State Building, pennies just aren't shaped for killing.