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Asked by elliejade to Asif, Laura, Lena, Sean, Viv on 15 Mar 2012.
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Sean Murphy answered on 14 Mar 2012:
A pound coin dropped from the Empire State Building wouldn’t reach the floor due to the updrafts and roofs of the lower floors.
Mythbusters also tested this
http://dsc.discovery.com/videos/mythbusters-penny-drop-minimyth.html
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Lena Ciric answered on 15 Mar 2012:
Great video! I wish I was a mythbuster. The science they do is ALWAYS fun.
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Laura Waters answered on 15 Mar 2012:
If it was a REALLY big coin it would but then that wouldn’t count I don’t think!
Comments
elliejade commented on :
Okay but if it was just straight down how long do you predict it would take?
Sean commented on :
Dimensions of a UK pound coin:
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
Drag force = (1/2) CD rho A V^2
where
A is the frontal area
CD is the drag coefficient.
rho is the density of air = 1.2 kg/m^3
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
tatesnow commented on :
That’s crazy, i worked it out exactly the same! Brownie points, Sean!
Sean commented on :
Height of Empire state building = 381 meters
So @ 148m/s, about 2.57 seconds