see Mythbusters. They did this experiment and the terminal velocity of a falling penny precludes it being dangeerous
When you start a thread, it’s helpful to other readers to provide a link to the column under discussion; saves search time and keeps us on the same page. In this case, I presume: http://www.straightdope.com/columns/read/205/would-a-penny-dropped-from-the-empire-state-building-kill-someone-on-the-ground
Thanks for the Mythbusters ref, mkmkmk. Of course, they do a single experiment, which neither proves nor disproves anything, really. Just because one penny (or a handful) doesn’t do any damage doesn’t mean on another day, that a different penny couldn’t. Cecil says no penny can, and cites the physics, which to my mind is more impressive than just testing a small sample. (That’s my complaint with Mythbusters in general, their assumption that one experiment can prove or disprove some myth.)
But Mythbusters often cite the physics. They get the voiceover guy and that blue board with the white crayon.
Also, Cecil cites pure gravity and no wind resistance. He doesn’t take drag into account. Sure, after he proves it won’t cause damage with no drag, he goes on to suggest the penny might tumble and slow further.
But here’s the thing: The Mythbusters demonstrated that the coin would tumble. Not could tumble, but would tumble. Then they measured the terminal velocity of a tumbling coin. That’s data, man.
And to top it off, they actually hit someone with a coin at that velocity. I don’t see [del]Cecil[/del] Little Ed catching pennies from the sky to answer the column.
I will grant you that sometimes (often) they claim conclusive results from limited test samples, and perhaps that isn’t warranted. But this case doesn’t count, in my opinion.
However, it is fair to point out that Cecil wrote this article in 1981, long before the Mythbusters did anything.
And it should be pointed out that a single sample CAN disprove something, if the single sample has all things true in the hypothesis, but results in a truly opposite conclusion. Thus, if the assertion is that, given the following conditions, a certain result is impossible, and you replicate the conditions and achieve the “impossible” result, you have just disproved the impossibility.
Further, Unca Cece’s statement proves absolutely nothing. His physics lecture is particularly unimpressive, since he calculates that the penny will hit the ground at a speed roughly 1/5th the velocity of a bullet leaving the muzzle of the gun; why would that NOT be sufficient to break through the skin and skull of someone (since, as he notes, the penny is about the same weight as the bullet)? Further, he doesn’t even address the issue of terminal velocity, or attempt to calculate it. And as for “tumbling”, if by this he means spinning, that actually will make the penny go FASTER than if it floated down as a disc parallel to the ground.
But what I hope Dex is saying is that attempting to establish an impossibility by one example of something not happening is not sufficient to prove the impossibility. In this he is correct.
Sorry gang but you couldn’t hit the ground from the top of the Empire State Building with a baseball thrown by a professional pitcher, never mind a penny! The building covers what, four city blocks and the observatory is in the center! All a penny (or a baseball) could possibly hit would be the building itself!
Now if the World Trade Towers were still there and you could get to the edge where it was open, that would be a different story.
Yes, that’s what I was trying to say. A single example can disprove a general rule: that is, “all zebras are black-and-white” is disproved by finding one purple-and-green zebra, but the rule “some dogs are black and white” is not disproved by finding a brown dog. In this case, it’s whether a penny dropped etc CAN cause damage, not MUST.
And Cecil DID in fact mention wind resistance.
Living in (or at least near New York), I can tell you the Empire State building takes up a 1/3 of a block, and it is mainly tower. You probably couldn’t toss a baseball or penny off the East or West side without hitting the building unless you really had a good throwing arm. However, the South and North sides of the observation deck is probably close enough to the outside of the building that you could toss a penny or baseball off to the sidewalk.
Here’s a link to Google Maps of the building: http://maps.google.com/maps?client=safari&oe=UTF-8&ie=UTF8&q=empire+state+building,+new+york+ny&fb=1&gl=us&hq=Empire+State+Building&hnear=Empire+State+Building&cid=0,0,14096438994681097860&ei=t74rS6KvIMSztgeDybiMCQ&ved=0CA8QnwIwAA&ll=40.748505,-73.985681&spn=0.001079,0.001966&t=h&z=19
You can see the South side of the observation desk. If you could toss something about 25 feet outward from there, you could hit the sidewalk. Note there are two observation desks. The main one with all the people crowded around and second higher level that’s actually inside the round tower. Most people don’t bother with the inside observation desk in the round tower because it takes even longer to get in, costs extra, and you don’t really get a better view.
That’s not exactly addressing the issue.
He said “for the moment” and then went on:
Cecil, hisownself, wonders if he oughtta rethink the penny issue in the Bullet fired into the air column.
As I noted, if by “tumbling” we are talking spinning, then this would presumably speed the penny up, not slow it down. “Updrafts” are not “wind resistance” per se, but rather an added effect upon the penny from air movement. “Wind resistance” is the simple issue of the effect upon an object of moving through air, which offers a resistance to that movement. It is wind resistance that causes an object to have a “terminal velocity”. And nothing of what Unca Cece was saying in that article addresses the effects of it in the least bit.
Depends on what you’re comparing to. You’re correct, of course, that a tumbling penny will have less resistance than one dropped parallel to the ground, but a tumbling penny will have more air resistance than one dropped edge-first.
(The refs I can find call calculating the drag on a tumbling disk a nasty problem, but give a reasonble estimate of a Cd of about 0.7 or 0.8 based on the disk’s frontal area, v. 1.18 for a face-first disk. Here’s one ref. Also, for completeness, something the size and weight of a penny will absolutely tumble. Here’s a nice paper on tumbling disks, nondimensionalized. A penny in air has nondimensional inertia I* of about 18 and a Reynold’s number at terminal velocity of about 20,000, putting it far up into the tumbling regime of Figure 3)
Although in general I agree with you about Mythbusters’ lack of rigor, I thought this was one of their better tests. They did the math at the beginning to get the terminal velocity for the bounding cases (face-first and edge-first, as calculated here). Which, to be blunt, was better physics than Cecil showed. Then they showed an actual penny tumbles, maintaining a terminal velocity between the two. And finally they shot the penny at the top-end bounding velocity, without any real harm. You can quibble with that last part being not necessarily rigorous, but I think you’d have to present some pretty decent evidence on why one would expect their handful of tests not to be representative of an extreme case.
I would think that the likelihood of a penny managing to maintain an orientation thin edge down through the air would be slim to none. Perhaps if it had some spin going already around an axis orthogonal to the plane of the penny and through its center of gravity…
I’ll have to read that article later tonight. That looks interesting, but the science will probably force me to go learn one or two pre-requisite concepts.
Closer to “none;” disks moving edge-first are unstable. However, for large Reynold’s numbers (i.e., higher velocities), disks moving face-first are also unstable. So for a large drop distance, the penny is certain to wind up tumbling. And the terminal velocity of a tumbling disk winds up, as might be intuitive, to be between that of an edge-first and face-first disk, which is what Mythbusters showed experimentally.
What I’d like to know is if there are “please don’t throw pennies off the observation deck” signs up there. (Though these days tossing ANYTHING off the Empire State Building would probably be grounds for a visit by the Department of Homeland Security.)
Well, I have taken a hit from a nickle falling 3 stories right on my forearm and can say that it hurt like hell and left a very large bruise, although it was not merely tossed but thrown straight down, not sure if that makes a difference but I’m positive a penny from that height could cause harm, even though hitting someone would be near impossible.
From about 3 stories, throwing might make a mild difference, but from any significant height the air resistance will slow the penny (or nickel) down if it is thrown faster than terminal velocity of a tumbling penny (or nickel).
What you received is probably the worst a coin could do. It will hurt, it might bruise, but it didn’t penetrate the skin, nevermind your skull.
Dropped a water balloon on the back of a young lady unprepared to be hit with an unprepared water balloon. It was not-nearly-as-entertaining as the original hit, though she jumped up, exposing herself.
Wikipedia gives their take on this issue:
I don’t think the wiki article wanted to use the word “bias”: “Address their topics conclusively”, might be better.