What happens if you drop a penny off the Empire State Building? This question fuels a long-standing urban legend, suggesting a small coin accelerated by gravity could become a deadly projectile. This misconception often evokes images of a penny piercing sidewalks or causing severe injury. However, the scientific reality tells a different story.
The Physics of Falling
Objects falling through Earth’s atmosphere are subject to more than just the pull of gravity. While gravity continuously accelerates an object downward, another force, known as air resistance or drag, simultaneously acts in the opposite direction. Air resistance increases as an object’s speed increases, creating a counteracting force against gravity.
Eventually, for any falling object, 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. The object then continues to fall at a constant speed, which is known as its terminal velocity. Factors such as an object’s mass, shape, and surface area significantly influence its terminal velocity. A lighter object with a larger surface area relative to its mass will experience greater air resistance and reach a lower terminal velocity more quickly.
The Penny’s Minimal Impact
Applying these physical principles to a penny reveals why the urban legend is false. A penny, being light and relatively flat, encounters substantial air resistance as it falls. It reaches its terminal velocity within a short distance, around 50 feet (15 meters) of descent. This means that even when dropped from the Empire State Building, which stands over 1,250 feet tall, the penny does not continue to accelerate throughout its entire fall.
The terminal velocity of a penny is about 25 to 50 miles per hour (40 to 80 kilometers per hour). At this speed, the impact force of a 2.5-gram penny is minimal, not enough to cause serious injury or damage. Its force is comparable to a raindrop or a small tossed pebble, resulting in little more than a sting. The myth persists because people overestimate gravity’s effect and fail to account for air resistance, associating a famous landmark with an exaggerated fear of falling objects.