Image: California State Controller's Office
City-slickers: Have you ever worried that, at any moment, you could be struck dead by a penny flung off the roof of a nearby skyscraper?
You can rest easy — on that score, at least. In fact, it's extremely difficult to turn a penny into a lethal weapon, and hurling it over the barricades at the top of the Empire State Building won't get the job done. Even from that height, a penny is too small and flat, and cushioned by too much air, to become a torpedo.
Instead, it would flutter to the ground, like a leaf. If it did strike you, it would feel like being flicked in the forehead — "but not even very hard," said Louis Bloomfield, a physicist at the University of Virginia. And he should know. He recently used wind tunnels and helium balloons to replicate the fall of pennies from skyscrapers. When experimental pennies struck him, it didn't hurt. "I think one bounced off my face once," Bloomfield told Life's Little Mysteries.
People mistakenly assume that a falling penny, subject to the force of gravity, will accelerate for the entirety of its fall, achieving breakneck speeds by the time it reaches the ground. This would indeed happen if New York City was evacuated — that is, if all the air were removed and the penny was tossed off the Empire State Building into a vacuum — but as things are, collisions with air molecules slow falling pennies down. Called a "drag force," air resistance opposes the penny's downward motion, counteracting the force of gravity. [6 Weird Facts About Gravity]
The faster the penny falls, the greater the air resistance it experiences, and so at a certain maximum velocity of the penny, the drag force becomes equal and opposite to the downward gravitational force. With the two forces balanced, the penny no longer accelerates. Instead it falls at a constant speed, called the terminal velocity, all the way to the ground.
Pennies are flat, so they experience a lot of air resistance, and they are light, so it doesn't take much drag to counteract their weight. Thus, if hurled off a skyscraper, pennies achieve their terminal velocity after only about 50 feet (15 meters) of descent. After that point, they flutter to the ground at a measly 25 mph (40 kph), Bloomfield said.
If there were no air, a falling penny would accelerate to a speed of 208 mph (335 kph) by the time it reached the ground (or your head). At that speed, it might very well damage your skull, but it wouldn't drill through.
"A penny is pretty much a little nothing," Bloomfield said. "It's not a very compact object. It doesn't drill into you very well."
But don't take off that protective head gear just yet. Falling ballpoint pens are the real danger. If someone nonchalantly tossed one of those off the top of the Empire State Building, it could kill. Depending on their design, pens will either spin and flutter, or shoot down like an arrow. In the latter case, "it might well come down at 200 mph," Bloomfield said. "When it hits, it will hit a small area with a lot of momentum. It will chip the sidewalk. It could punch into a wooden board. You wouldn't want it to hit your head."
- Smart Answers for Crazy Hypothetical Questions
- How to Make the Penny Worth 1 Cent Again
- How to Survive an Elevator Free Fall
Copyright 2012 Lifes Little Mysteries, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
See what we're tweeting about
13 Comments
Add CommentFor anyone who had secret fantasies about poetic justice on Wall Street... dream on...
Reply | Report Abuse | Link to thisInteresting that a penny thrown from a tall building is relatively harmless, but could be deadly in a vacuum. Dropping a penny into a Republican presidential debate could be very dangerous...
Reply | Report Abuse | Link to thishmm. but if you were to say, attach a bit of ribbon to the penny - just enough to keep it falling edge on, it would be far more aerodynamic. Since it would not be tumbling, it could reach far higher speeds. I'm sure it would still reach a terminal velocity far below that of falling in a vacuum, but it'd be interesting to know just how fast.
Reply | Report Abuse | Link to thisHow long ago was it that Mythbusters thoroughly covered this urban legend? However, it will sting like the dickens if it hits someone! (Yes, they covered that too...)
Reply | Report Abuse | Link to thisI wonder how many times pens have been dropped off from one of the many offices in one of the many skyscrapers, people are just like they haven't been hit by them?
Reply | Report Abuse | Link to thisI suppose you are right. Considering you would not have any pennies at all with the democrats in control and on their socialist pillaging of everything we own and the spending insanity they are on.
Reply | Report Abuse | Link to thisNow we are going to have to put a wait period on buying pens (and pencils) since they could be used as weapons by terrorists throwing box loads of them off all the skyscrapers in New York at rush hour.
Reply | Report Abuse | Link to thisNo. Among my many concerns about being hit by a falling object from a tall building, a penny was not among them.
Reply | Report Abuse | Link to this"It is entirely possible that a penny dropped of the tallest building in the world might fall into the chamber of a penny gun with the resulting impact cauing the gun to go off, firing the penny into someone's heart and killing them.
Reply | Report Abuse | Link to thisOr Magneto might find it on the ground and use his mutant powers over metal to push it through someone's head.
So yes, a falling penny can indeed kill someone."
Don't forget choking hazards, copper allergies, cranial pressure relief holes, and how soft the human eye is...
" "Dropping a penny into a Republican presidential debate could be very dangerous..."
Reply | Report Abuse | Link to thisYou mean that those Republican low lifes might kill each other as they grub for the small change they might see on the stage? "
No, it's dangerous because the number of life times they would expend trying to find a way to tax that one penny the value of the entire national debt while taxing the rich nothing (since of course that would mean jobs lost, because of course only the rich supply jobs. And if a poor person is somehow able to start a business and start employing people, well it's pretty obvious he's not been paying his taxes...) ROFL
Pennies should be scattered at Tea Party rallies. Tea Party mouth-breathers are known for their fastidious litter picking skills, imagine the time and effort they'd expend picking up every last penny. If this is done regularly, quite a few of the misbegotten home-schooled cretins will choose to stay home and count their blessings.
Reply | Report Abuse | Link to thisA doubt, related to the falling penny question. If somebody points a pistol or a rifle at the sky, and fires it, can the bullet harm somebody in its way down from the top height reached, taking into the account the braking affect of the atmosphere ?
Reply | Report Abuse | Link to thisDavid Letterman threw a water melon off a building. But, that was waaaaay before he threw his career off the intern.
Reply | Report Abuse | Link to this