From: Lee Corbin (lcorbin@tsoft.com)
Date: Sat Oct 12 2002 - 21:44:46 MDT
Robert wrote in some thread
> Each collapse triggered a 2.7 richter earthquake. Each tower was
> about 40,000 tons of material (not pounds). That's 80 million
> pounds of material, striking the earth at 250 mph (367 fps).
> Kinetic energy equals mass times velocity squared, or
> 10,775,120,000,000 ft-lbs/sec for each tower collapse.
> How many tons of TNT is that equal to?
Energy should come out in ft-lbs, and one foot-pound apparently
is 1.356 joules (I looked it up---my failure to work this out
from first principles is humiliating). So if you are correct,
then this translates to 1.07 x 10^13 joules, no?
A handy thing to remember whenever you're thinking of how
much megatonnage a volcano requires to throw some immense
mass a half-mile into the air, or thinking about how many
H-bombs it would take to literally blow up the world (i.e.,
give every atom of the Earth escape velocity) is
1 megaton = 4x10^15 joules.
In fact, the source for this is my old copy of "Spacetime
Physics" by Taylor and Wheeler, p. 136. Two of the factors
they use to derive this are "10^3 calories/gram of TNT-
equivalent" and "10^6 grams per ton", so we know that this
is a pretty rough calculation.
Anyway, your 1.07 x 10^13 joules works out to about .0027
megaton, or 2.7 thousand tons of TNT. The little Hiroshima
bomb was 5,000 kilo-tons, I believe.
Lee
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