2p coin dropped from the Eifel Tower!

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Offline Seany

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2p coin dropped from the Eifel Tower!
« on: 13/07/2007 15:44:51 »
Apparently.. When it is dropped from the Eifel Tower, and lands on somebody's arm at the bottom, it can cut through it.

Is this real? Is there such power when it falls and reaches terminal velocity?

If it is true.. What would happen if I spat out the Eifel Tower?
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Offline DoctorBeaver

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2p coin dropped from the Eifel Tower!
« Reply #1 on: 13/07/2007 16:17:59 »
How could you spit out the Eiffel tower? You couldn't fit it in your mouth!  [:D]

I don't know about cutting someone's arm off, but it would certainly do a lot of damage.
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another_someone

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2p coin dropped from the Eifel Tower!
« Reply #2 on: 13/07/2007 18:51:34 »
As Eth said, it can do a fair amount of damage, and could penetrate bone (i.e. if it hit you on the head, it could penetrate your skull, and enter your brain); but it would not be physically large enough to take an entire arm off.

Spit has a much larger surface area for the same mass, so its terminal velocity would be far less (and could possibly break up during the fall anyway).

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Offline that mad man

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2p coin dropped from the Eifel Tower!
« Reply #3 on: 14/07/2007 18:35:41 »
Unfortunately its a myth.  [:0]

The coins terminal velocity would be to low to do much damage.

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Offline DoctorBeaver

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2p coin dropped from the Eifel Tower!
« Reply #4 on: 14/07/2007 19:39:40 »
Here are the pertinent figures. I'll leave it to someone who knows how to calculate what kind of damage it could do.

Terminal velocity - 24-75mph depending on the coin's orientation during descent.
Weight - 7.12g
Thickness - 1.85mm

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another_someone

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2p coin dropped from the Eifel Tower!
« Reply #5 on: 14/07/2007 21:36:27 »
Ofcourse, the other factor that has been overlooked is that I suspect that the curvature of the outside of the Eiffel tower, being that it is much wider at the base than at the top, would probably make it very difficult to hit somebody on the ground with something dropped from the top.

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Offline DoctorBeaver

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2p coin dropped from the Eifel Tower!
« Reply #6 on: 14/07/2007 21:38:52 »
Ofcourse, the other factor that has been overlooked is that I suspect that the curvature of the outside of the Eiffel tower, being that it is much wider at the base than at the top, would probably make it very difficult to hit somebody on the ground with something dropped from the top.

Catapult?  [:D]
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another_someone

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2p coin dropped from the Eifel Tower!
« Reply #7 on: 14/07/2007 21:40:13 »
Here are the pertinent figures. I'll leave it to someone who knows how to calculate what kind of damage it could do.

Terminal velocity - 24-75mph depending on the coin's orientation during descent.
Weight - 7.12g
Thickness - 1.85mm

75mph is very much lower than I would have expected.  It is certainly very much lower than the velocity of an average bullet (even the subsonic ones from a small handgun), and the mass I would imagine would be comparable to the mass of a bullet.

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Offline DoctorBeaver

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2p coin dropped from the Eifel Tower!
« Reply #8 on: 14/07/2007 21:42:39 »
The figure of 24-75mph was for a US penny. I don't know how that compares sizewise with a 2p coin.

I must admit, I expected it to be much higher.
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Offline ukmicky

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2p coin dropped from the Eifel Tower!
« Reply #9 on: 15/07/2007 00:28:42 »
it would also depend on how it fell,if it tumbles then its velocity would be quite slow compared toedge on.

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Offline DoctorBeaver

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2p coin dropped from the Eifel Tower!
« Reply #10 on: 15/07/2007 00:57:04 »
it would also depend on how it fell,if it tumbles then its velocity would be quite slow compared toedge on.

That's why the velocity was stated as 24-75mph.
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Offline eric l

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2p coin dropped from the Eifel Tower!
« Reply #11 on: 15/07/2007 08:49:36 »
On a long drop, would a tumbling coin not be "braked" into falling straight on (oriented vertically) just to reduce drag ?  Or would the drag force it into a horizontal orientation ?
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Offline DoctorBeaver

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2p coin dropped from the Eifel Tower!
« Reply #12 on: 15/07/2007 09:10:01 »
On a long drop, would a tumbling coin not be "braked" into falling straight on (oriented vertically) just to reduce drag ?  Or would the drag force it into a horizontal orientation ?

I would certainly expect that to happen. Unless, of course, enough spin was imparted for it not to. Or what about turbulence... cvould that affect its orientation?
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Offline Soul Surfer

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2p coin dropped from the Eifel Tower!
« Reply #13 on: 15/07/2007 11:04:47 »
Assuming that the coin was dropped vertically as it accelerated almost any dissimilarity between the two sides would cause it to rotate and fly sideways a bit as it fell It would then probebly fly flat for a while slowing down its downward fall its angular momentum wout make it turn upwards a bit and eventually it will fall back in the other direction repeating the process.  Try dropping a coin into water you will see the same process happening much more slowly and on a smaller scale.
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Offline lightarrow

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2p coin dropped from the Eifel Tower!
« Reply #14 on: 15/07/2007 11:05:08 »
Ofcourse, the other factor that has been overlooked is that I suspect that the curvature of the outside of the Eiffel tower, being that it is much wider at the base than at the top, would probably make it very difficult to hit somebody on the ground with something dropped from the top.
You can throw it with normal force; the coin has time to move horizontally far enough.

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Offline lightarrow

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2p coin dropped from the Eifel Tower!
« Reply #15 on: 15/07/2007 11:13:43 »
Here are the pertinent figures. I'll leave it to someone who knows how to calculate what kind of damage it could do.

Terminal velocity - 24-75mph depending on the coin's orientation during descent.
Weight - 7.12g
Thickness - 1.85mm

That means, at 75mph, a kinetic energy = 51.264 Joule.
A 4.5 millimetres lead pellet with ~ 20 Joule of kinetic energy can penetrate through the skull. Clearly a coin is much larger than 4.5 mm, however 51.26 Joule are a lot, and if the coin hits you with the edge, it could probably break the bone; I wouldn't feel my head safe...
« Last Edit: 15/07/2007 11:20:51 by lightarrow »

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Offline Bored chemist

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2p coin dropped from the Eifel Tower!
« Reply #16 on: 15/07/2007 13:54:17 »
The coin is pretty much bound to tumble, that drops the speed roughly 3 fold and the energy 9 fold; 5J is a lot easier to deal with.
The question is debated here
http://www2b.abc.net.au/science/k2/stn/archives/archive101/newposts/2089/topic2089158.shtm
and they point out that the mythbusters team tried firing coins about. They hurt, but they wouldn't kill you unless you were really unlucky.
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Offline JimBob

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2p coin dropped from the Eifel Tower!
« Reply #17 on: 16/07/2007 04:36:17 »


Can't resist posting this - not totally off topic
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Offline DoctorBeaver

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2p coin dropped from the Eifel Tower!
« Reply #18 on: 16/07/2007 07:35:12 »
 
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