The Killing Coin

We’ve all heard the Urban myth at least once. Throw a coin from the top of the Empire State Building and it hits and impales the person standing on the ground below. But is it possible?

Can a Coin Dropped From a High Building Kill Someone?

Come to think of it, a bullet doesn’t weigh much, but it can penetrate someone’s flesh and even skull. Is it the same case with a penny? Turns out, it isn’t. A bullet is able to pierce through a skull because of its velocity. In short, a coin thrown from a high building can not attend enough velocity. Let me explain a bit.

When an object is released from the rest towards the ground, it experiences acceleration due to the force of gravity. The object starts accelerating at the rate of 9.8 ms^-2. Due to the presence of air however, the accelerating object starts to experience an upwards force of drag (as shown in the image). After sometime, the drag increases and cancels out the acceleration due to the force of gravity. The object then moves at a constant velocity called the terminal velocity.

Due to the presence of air and the flatness of the coin, it experiences very high air resistance. An article in the Scientific American reports that the terminal velocity of a coin is about 40 kmph which is not enough to even break skin. The actual terminal velocity depends on a lot of factors including humidity, temperature and others. The article goes on to report that in the absence of air (in vaccum), a coin can reach the terminal velocity of about 335 kmph. It is enough to cause serious damage even if it won’t drill through your skull.

Friendly advice: Although it doesn’t kill people down below. Don’t do it. Save your coins!