The idea of a penny dropped from a skyscraper, such as the Empire State Building, becoming a deadly projectile, is a persistent urban legend. This myth suggests a small coin, accelerated by gravity, could gain enough speed to cause serious injury or even be lethal upon impact. This enduring fascination prompts a closer examination of the scientific principles governing falling objects and the actual consequences.
The Science of Falling: Air Resistance and Terminal Velocity
Objects accelerate towards Earth due to gravity, but their speed does not increase indefinitely. As an object falls, it encounters air resistance, a force that opposes its downward motion. Air resistance increases with the object’s speed, its cross-sectional area, and the density of the air. Eventually, the upward force of air resistance becomes equal to the downward force of gravity. At this point, the net force on the object becomes zero, and it stops accelerating, falling at a constant maximum speed known as terminal velocity.
An object’s terminal velocity is determined by its mass, shape, and surface area. For instance, a feather has a much lower terminal velocity than a bowling ball because it has a larger surface area relative to its mass, encountering more air resistance at lower speeds. A typical US penny, weighing about 2.5 grams and having a relatively flat shape, reaches its terminal velocity fairly quickly. Its small mass and shape prevent it from accelerating to extreme speeds, as air resistance rapidly balances the gravitational pull. This occurs when the penny is falling at approximately 25 to 50 miles per hour.
The Reality of a Falling Penny’s Impact
Considering the principles of air resistance and terminal velocity, a penny dropped from a great height would not achieve the destructive force often imagined. Once it reaches its relatively low terminal velocity, its kinetic energy remains limited. The impact of a penny traveling at this speed would be comparable to being struck by a raindrop or flicked by a fingernail. While it might sting slightly or cause a minor red mark, it would not penetrate skin or cause a serious injury.
The energy transferred upon impact from a penny at terminal velocity is too low to be lethal or cause significant damage. For comparison, a typical raindrop hits the ground at about 17 to 20 miles per hour, and its impact is barely noticeable. The myth of a deadly falling penny drastically overestimates the speed and kinetic energy a small, light object can accumulate. The idea of a penny becoming a dangerous projectile capable of causing severe harm is not supported by physics.
Beyond Pennies: Why Throwing Objects is Dangerous and Illegal
While a penny dropped from a skyscraper poses minimal physical threat, throwing any object from a tall building is inherently dangerous and carries significant risks. Even a seemingly harmless item can become unpredictable due to wind currents, potentially striking an unintended target. The danger is amplified if the object is heavier or larger, as it could cause severe injury or even death. For example, a heavier object like a cell phone could cause serious harm due to its greater mass.
Throwing objects from tall structures is illegal and can lead to severe legal consequences. Such actions are considered reckless endangerment, a criminal offense that can result in fines or imprisonment, even if no one is injured. If an object thrown causes injury, charges could escalate to assault or more serious offenses, depending on the intent and outcome. The act of throwing anything from a building is a serious matter with significant legal and safety ramifications.