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Can a Penny Dropped from a Skyscraper Kill a Person

February 6th, 2009

If you dropped a penny off of a skyscraper and it landed on a person below, could it kill him?  The simple and possibly surprising answer is no.  The reason some people may believe that a falling penny could kill a person is that as an object falls, the force of gravity causes it to accelerate.  The idea is that the penny could potentially fall with such speed that its force on impact with a person could be deadly.  This logic is slightly flawed, however, in that it fails to take into account some of the other principles of physics.  Although an object will accelerate while falling as a result of gravity, there is a limit to this acceleration.  This limit is known as terminal velocity and is determined by an object’s weight and any drag forces that are acting upon that object as it accelerates.  For a penny, the terminal velocity would be between forty and sixty miles per hour.  While this is rather fast, and may lead you to think that a falling penny can in fact kill a person, a penny’s mass is so small that it actually will not result in much bodily harm.  It may cause a cut or a bruise but it will not have the force to kill.  One must also consider that there are strong updrafts that surround tall buildings.  These updrafts would slow down the acceleration of the penny so that it probably would not be traveling at terminal velocity when it reached the point of impact.  Finally, the shape of a penny makes it relatively harmless.  If the penny were shaped more like a bullet, it could potentially become lodged in the unlucky person below and cause serious injury or death.  Therefore, taking into account a penny’s shape, mass and resistance encountered on the way down, a penny dropped from a building cannot kill a person.

  1. February 6th, 2009 at 22:11 | #1

    Good example to direct our thinking about some principles of physics. But writer must have given attention to the way penny falls. Is it falling the flat side verticle or hrizontal?

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