Could a penny dropped from a skyscraper kill someone?

A penny dropped from the Empire State Building or a similar skyscraper is very unlikely to kill anyone. It is small, light and flat, so air slows it to a modest speed long before it reaches the ground. Physicist Louis Bloomfield of the University of Virginia, who tested falling pennies, said being hit would feel like a flick on the forehead, and not even a hard one. A University of Leicester student paper reached a similar conclusion: the penny would not reach a speed sufficient to kill or badly injure anyone, though it would be painful. [1] [2]

The myth assumes that gravity keeps accelerating the coin for the whole fall. In a vacuum that would happen, and the penny would reach about 208 to 209 mph at the sidewalk. At that speed it could damage a skull or a pavement slab, though Bloomfield said it still would not drill into a person, because a penny is not a compact object. [1] [3]

Air exerts an upward drag force that grows as the coin speeds up. When drag equals the penny's weight, acceleration stops and the coin falls at a steady terminal velocity. A penny tumbles and flutters like a leaf, leaving a broad turbulent wake, so it reaches terminal velocity at only about 25 mph (40 km/h). Bloomfield tested this in a small vertical wind tunnel, where the penny hovered when the air moved upward at about that speed. Reports say the coin reaches this speed after roughly 50 feet (15 meters) of falling. [3] [1] [4]

Estimates vary a little by source. The University of Illinois gives a terminal velocity of 30 to 50 mph depending on conditions, and notes that even at 50 mph the penny's momentum is tiny. The Naked Scientists put the speed lower, perhaps 5 to 10 meters per second (15 to 20 mph), and note that you could throw a penny that hard by hand. [5] [6]

The Illinois article adds that the Empire State Building tapers, so a penny dropped from the top would likely strike the building's side. The Naked Scientists note that a penny spun like a wheel would slice through air with less resistance, move faster and could hit edge-on, making it more dangerous, though they do not claim it would be lethal. [5] [6]

Heavier or more streamlined objects are a different matter. HowStuffWorks says a roll of 50 pennies, about 125 grams, falling from around 1,400 feet could strike at about 20 mph and deal a deadly blow to the head. Bloomfield said a ballpoint pen that falls point-first might reach about 200 mph and could kill, while one that flutters would not. [4] [1]