Although I agree with Cecil’s conclusion/speculation that a penny dropped from the ESB would not kill (or otherwise “pass right through”) an unwitting pedestrian below, I think his equating a penny’s mass with that of a .22 bullet is incorrect.
Let’s remember: pennies today are made of aluminum (or “aluminium,” if you’re a Brit), meaning that the dropped penny has even less mass to counteract the stiff wind resistance and tumbling action in its fall.
More likely (here’s my wild speculation), the pedestrian would barely feel anything.
Pick up a newly minted penny. It’s incredibly light.
Unconvinced? Meet me at the Empire State Building. I’ll prove it. I’ll even bring my own roll of pennies, so that we can replicate my findings dozens of times. (Note: I trust you have a very, very big head.)
That was one of the worst Cecil columns I’ve ever read. It didn’t answer the question at all. Even I know more about dropping pennies off the Empire State Building than was covered in that column, much of which I learned from watching that moronic Urban Legends show they had on MTV last season. And when you’re learning more from Viacom than from the world’s smartest man, there’s definitely a problem. Sure, the column is 20 years old, but that’s no excuse. I’m disappointed in Cecil.
It will come as no surprise that people of varying degrees of mental health have been curious about the terminal velocity of pennies for some years.
Fortunately, we do not need to guess, since the question has been answered by direct experiment, and discussed in the alt.folklore.urban newsgroup.
In this delightful thread, we have an honest-to-God expert in Dennis Thompson of NASA, reporting on his own experience with falling objects at NASA’s Zero Gravity Research Facility at the Lewis Research Center in Cleveland. As a bonus, we have his response to a stunningly clueless (and mercifully anonymous) poster.
An afterthought: It would be interesting to see how much the DNA of the AFU and the SDMB have mingled over the years.
My brother heard a radio interview recently about this question. Because of the way the Empire State Building is shaped, the pennies don’t reach the ground.
The top of the building is very narrow, getting wider as it goes down. The pennies land on various ledges and stages of the building on the way down. There is one ledge in particular where almost all of the pennies land.
In Cecil’s column, he says officials claim no one has ever thrown anything off the building. In this interview they were finally admitting that people do.
The current zinc Lincoln cent is 19mm in diameter and weighs 2.50g (down from the 3.11g copper cent), which is a noticable, but not enormous, decrease in weight.
For a super-duper rough calculation of terminal velocity, calculate drag = 1/2[symbol]r[/symbol]C[sub]D[/sub]V[sup]2[/sup]A, where
[symbol]r[/symbol] = air density = 1.28 kg/m[sup]3[/sup]
C[sub]D[/sub] = drag coefficient ~= 1.1
V = velocity
A = penny area = 283 mm[sup]2[/sup] = 0.000283 m[sup]2[/sup]
Equate this to the weight of the penny (0.0025kg X 9.81m/s[sup]2[/sup] = 0.0245 N):
0.0245N = 1/2 X 1.28 kg/m[sup]3[/sup] X 1.1 X V[sup]2[/sup] X 0.000283 m[sup]2[/sup]
V[sup]2[/sup] = 123 (m/s)[sup]2[/sup]
V = 11.1 m/s = 24.8 mph is the terminal velocity. Since this doesn’t include the effect of tumbling, it’s probably not a real accurate estimation, but it should give a feel for the magnitude of the velocity.
Damn you, Q.E.D. Damn you to hell. I blame you for this travesty.
Once upon a time, a fellow could produce a rather melodious jingle in his pocket. Whole cities bristled with men merrily jingling their pocket coinage.
I like lingqi’s experiment, but I have to wonder aloud if there aren’t some important nuances that may not be incorporated in it. And before I start, let me just say that I expect lingqi’s findings are undoubtedly very close to providing a damn good answer.
Question #1: isn’t linqi just dragging the penny behind his or her car like a kite?
In other words, the string potentially acts to keep the flat face of the penny always turned into the wind (depending upon how it is attached, but presuming that it is attached at or near the center, for instance). This wipes out the effect that tumbling has on the object’s terminal velocity. I truly don’t know if this is a significant effect or not, but comparing the actions and speed of a kite “through” its media while fixed at a stable center, versus tumbling much more rapidly through that same wind when destabilized–and plunging straight at my head, I might add–I tend to think that the two motions could provide very different empirical results.
Question Two: Again, don’t know the answer to this, but is it possible–JUST POSSIBLE–that the penny could fall edgewise all the way to earth (frisbee-like), thereby presenting a vastly different (vastly smaller) frontal area from which to generate wind resistance? Or are the air perturbations and turbulence too great to ever allow this to happen? If it COULD happen, it would seem the terminal velocity could be much more in the range of the ball bearing than was assumed. A potential “Ouch!” at least.
Just thoughts, folks. Finer minds than mine know the answers. Show yourselves, ladies and gents, and kindly illuminate.
I would think that, if you glued a single thin string to the penny, it would be flexible enough to allow the penny to flutter. You should certainly avoid a stiff string or multiple strings. In any case. you’d be able to tell if this is an issue by observing the penny.
Doubtful; disks aren’t aerodynamically stable because the center of pressure and center of gravity are in the same place. Here’s a page explaining why with an experiment.
In the car-window experiment, the pennny is still free to tumble around an axis in line with the string. Now, there may be a difference between being allowed to tumble about one axis and being allowed to tumble about many, but since a penny is symmetric, I would tend to doubt it.
I think that lingqi’s experiment is as close as we’re going to get without actually dropping pennies from high places and clocking them with radar. I also strongly suspect that his experiment is fully adequate for the answer. Welcome, lingqi, and I hope that you make many more such posts in the future!
Yes, I can envision hundreds of experiments now taking place to determine, for example, the terminal velocity of string cheese, leather vests, parakeets, pudding cups, etc. all by dangling them out the window of a moving car.
Here’s a plug for the Straight Dope Bookstore. You need to buy some Striaght Dope Books.
In the 1970’s and 80’s, many a strange question was sent in from readers of Cecil’s column in the Balimore paper. And Cecil let them know it. Actually, after reading Cecil’s books, you would be convinced that the entire lunatic population of the US was consigned to Maryland back then. Hopefull things have changed.