What Would Happen If You Got Hit By A Penny Dropped From A Skyscraper?
The Penny Is Ultimately Slowed Down During Its Fall
Photo: foreverseptember / flickr / CC-BY-ND 2.0Anything falling from an immense height - say, the top of a skyscraper - is subject to the force of gravity. Because of this, you might assume that a falling penny would reach dangerous speeds. However, falling pennies are actually slowed down as they move, due to collisions with air molecules.
Air Resistance Builds The Faster The Penny Falls
The air resistance a penny experiences while falling is referred to as a “drag force.” This air resistance opposes the downward motion of the penny, and the air resistance builds the faster the penny falls. So, once the penny reaches the highest velocity it can possibly attain during its fall, the drag force counteracts gravitational forces.
The Penny Stops Accelerating Once Drag And Gravitational Forces Become Equal
Pennies experience quite a bit of air resistance because they are flat. The coins are also fairly lightweight, so it doesn’t take much drag force to counteract their weight against the force of gravity. Once the drag and gravitational forces become balanced, the penny no longer accelerates.
The Penny Is Still Moving Pretty Fast For A While
Once acceleration ceases, the penny falls at a constant speed all the way to the ground (or whatever or whomever it may run into beforehand). This constant speed is called the terminal velocity. Because pennies are lightweight and flat, they reach their terminal velocity after falling 50 feet. According to physicist Louis Bloomfield, the penny’s speed before reaching this velocity is documented to be around 208 miles per hour.
Once The Penny Reaches Its Constant Speed, It Falls At 25 Miles Per Hour
Once the first 50-foot stretch of a descent is reached, pennies slow down to fall at a constant 25 miles per hour. This speed is hardly enough to be lethal, especially when considering that a penny weights 1 gram. Even if one fell from the Empire State Building and reached speeds of 100 miles per hour before hitting its terminal velocity, it would have less than 1 foot-pound of energy on impact. Any collision would sting, at worst.
The Final Verdict
Ultimately, a penny tossed from a skyscraper would not kill someone. It may barely even hurt. Pennies are not sleek or aerodynamic, which causes them to move slower through the air. Because of this and their lightness, they fail to gather much speed. Getting hit by something with a gram of weight, slowly tumbling through the air, may sting a bit, but it wouldn't be lethal.
But Some Small Falling Objects Can Be Dangerous
Photo: dog97209 / flickr / CC-BY-NC-ND 2.0Though a falling penny may be relatively harmless, small falling objects can be seriously dangerous. Even ballpoint pens can be fatal if they from a certain height. Physicist Louis Bloomfield explains that a falling pen will hit a small area with a lot of momentum upon impact. According to him, a falling ballpoint pen could “chip the sidewalk,” or “punch into a wooden board.” So it's best not to toss anything off of a skyscraper.
If You Drop A Whole Roll Of Pennies From The Empire State Building On Someone's Head, It Could Be Fatal Unless They're Wearing A Hard Hat
Photo: Jim.henderson / Wikimedia Commons / CC0 1.0It's all physics when it comes to speed and impact of force. That penny you're dropping from the Empire State Building weighs about a gram, right? So according to a breakdown of weight vs. acceleration vs. impact, if you increase that to a 50-gram nut — or perhaps an entire roll of 50 pennies — and drop it the 1,000 feet from the top, it would, in theory, "reach a velocity of about 250 mph" if you don't calculate air resistance. This results in 100 foot-pounds, which could kill you at that force, unless, allegedly, you're wearing a hard hat.
