How can a penny kill you

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Create Account See Subscription Options. With a fury only the furies could conjure, the metal disc hurtles down with enough speed to incinerate the cat. But is The Simpsons the perfectly accurate guide to reality we all assume it to be?

Is the urban myth true: can a coin dropped from the top of a skyscraper actually kill someone? It couldn't even burn flesh — except in certain circumstances. All dropped objects experience constant acceleration — in other words, they go faster and faster, their speed constantly increasing, at a rate of just under 10 metres per second.

But air resistance also increases the further the object has fallen. When air resistance matches gravity, the object will achieve "terminal velocity" — maximum speed, after which it no longer accelerates. At a weight of 7. The actual speed it would reach depends on a variety of factors, from humidity to air pressure. Pennies are round and flat. When dropped from a tall building, they have as much power as falling leaves, according to Louis Bloomfield, a physicist at the University of Virginia, as reported by Scientific American.

Bloomfield experimented with wind tunnels and helium balloons to simulate a penny falling from a skyscraper. He was hit by a few of the coins and was unharmed. The only way a penny would accelerate to such a point that it would cause damage is if it was dropped from a tall building encapsulated in a vacuum in which all the air has been removed. In real life, a falling penny collides with air particles, which prevents the coin from accelerating. This resistance, or drag force, keeps the penny from rapidly moving downwards, which thwarts the force of gravity.

As the penny speeds up, it encounters more air resistance. The drag force and downward gravitational force balance each other, preventing the coin from accelerating.