9/11, the sheer scale of the collapse...

[max_tranmere]

I heard someone say years ago that if you dropped a coin off the top of the World Trade Centre it would shatter a paving stone as it hit the ground. I also heard that if you dropped a stale sandwich off the top (with an elastic band holding it together) it would go through the roof of a bus. Considering that, try and imagine what would have happened if you dropped a stone off the top - it doesn't bear thinking about. What would have happened if you dropped a paving slab from the top is too big a thing to try and contemplate in terms of the damage it would do on impact with the ground. Considering all those things, try and imagine what happened on September 11th 2001 when ONE AND A HALF MILLION TONS of masonry and steel came down in a matter of seconds. I'm surprised it didn't go through the world and out the other side. Makes you think doesn't it. I don't think an area of several square acres of the earth has ever had that much hit it, so hard, and so quickly - except Ground Zero at Hiroshima and Nagassaki in 1945 perhaps...

[Jonone]

[Essex Lad]

max_tranmere wrote:

> I heard someone say years ago that if you dropped a coin off
> the top of the World Trade Centre it would shatter a paving
> stone as it hit the ground. I also heard that if you dropped a
> stale sandwich off the top (with an elastic band holding it
> together) it would go through the roof of a bus.

Neither would penetrate either because when you drop something it will eventually reach terminal velocity which basically means it doesn't fall any faster when it reaches a set speed irrespective of how heavy or light the object is. In other words, if you dropped a coin off WTC or Big Ben and it hit you on the head it would hurt but would almost certainly not kill you.

[rgb]

Perhaps this is where Galileo went wrong with his famous experiment - he should have a thrown a stale sandwich held together with a rubber band from the Tower of Pisa.

[one eyed jack]

If you threw a bag of shit off the WTC it would hit the ground and splat so violently it would spray everyone with do-do for a mile around too.

I'm sure some crazy american or nutty tourist would've done all those things including the stone, coin and sandwich too.

I went to NYC last year and visited the Rockefeller and Empire State and came to this conclusion given the winds experienced on top that the impact of a coin hitting the ground wouldnt be that big a deal otherwise I'm sure many would've died over the years by random objects thrown off by random idiots trying to prove this impact theory

[mrmcfister]

There you go Max,take the right drugs and you'll think your sick bag is a six iron.Simple Simon said it right?Watch out when this junky satellite hits later today ...should make a crevice from here to Nigeria.

[JamesW]

"I heard someone say years ago that if you dropped a coin off the top of the World Trade Centre it would shatter a paving stone as it hit the ground."

You didn't say what kind of coin exactly?

For argument, let's say it was a UK Pound coin (Dimensions: diameter 22.5 mm, thickness 3.15 mm, mass 9.5 g).

At the terminal velocity, the aerodynamic drag force equals the weight.

Weight = 9.5e-3 x 9.81 = 0.093 N

where
A is the frontal area
CD is the drag coefficient.
rho is the density of air = 1.2 kg/m^3
Drag force = (1/2) CD rho A V^2

If it is falling flat, then
CD = 1.28
A = pi x 22.5^2 / 4 mm2 = 3.98e-4 m^2

0.5 x 1.28 x 1.2 x 3.98e-4 V^2 = 0.093

V = 17.4 m/s = 4.8 km/h, which is far too small to cause any damage

If it is falling edge first, the frontal area is
22.5 x 3.15 = 70.6 mm^2 = 7.06e-5 m^2
The drag coefficient would probably be about 0.1

0.5 x 0.1 x 1.2 x 7.06e-5 V^2 = 0.093
V = 148 m/s = 41 km/h

That would without question hurt you if it hit you on your head, but it's highly improbable that it would damage the pavement.

I believe that some years ago the TV show Mythbusters tackled this question using a US One Cent coin and their experiment concluded that if the cent hit anyone it would barely break their skin (if at all) and it certainly wouldn't have much impact on a paving stone.

[JamesW]

"I heard that if you dropped a stale sandwich off the top (with an elastic band holding it together) it would go through the roof of a bus."

In order to correctly compute the velocity of the stale sandwich can you fully detail the contents of the sandwich, i.e. ham, cheese or what? You also need to state exactly how stale the sandwich is as that would affect the size and mass, plus the shape of the sandwich matters as that would make a difference to the drag coefficient, so I need to know that too.

[max_tranmere]

Lots of interesting comments there. Thanks to JamesW who has really gone to town on this. I am only going on what I heard, "coin" and "sandwich" was the full extent of the brief, I never heard what size of coin or what might be in the sandwich, just "coin" and "sandwich".

I stood on top of the World Trade Centre when I visited New York in the 1990's. I remember the tower that did not have the radio mast was the one with the viewing platform on the roof that the tourists went up to. The height was incredible, you could turn around on the spot and see the whole circumference of Manhatten island, I heard also that if it rained you were too high to get wet as you were effectively above the clouds. I assume on a rainy day the rain clouds would form below the height of the 110th floor. If clouds were permanently there that would obscure the tourist's view of the ground from the roof and that wasn't the case - you could clearly see everything, but it was a sunny day.

I remember seeing signs telling people not to throw things over the edge, you couldn't get near the edge anyway, the tourists were in a crows-nest type thing that was slightly raised and in the middle of the large roof. I remember the lift to get from the ground to the 110th floor was super-quick.

Sadly no one will ever see that exact view again. RIP the 3,000.