[NBLUG/talk] OT: physic puzzle reviewed.

Walter Hansen gandalf at sonic.net
Fri Jan 9 17:04:00 PST 2004


    I just remembered somthing that might be a significant indicator (at
least approxamately). When they had the 100th aniversary of the bridge
they shut it down and let people stand on it. The bridge was full of
people and it was completely flat (no arch) from the weight. However
the engneers were furrious when they found out about the flatening as
the bridge was never built to withstand that much weight (being enough
weight to make it flat). The organizers of the event evidently didn't
check and believed that people couldn't possibly be heavier than cars.
(cars are about 20lbs per square foot parked bumper to bumper; people
are about 100lbs per square foot at a rock concert; also the people
were allowed to be on the walkways where the cars are not allowed)

     Anyway people are just a little less dense than water, so it would
take less than 5.5 feet of water on the bridge to bring it flat. Such
a wave would undoubtibly have several times that volume of water on
the bridge for at least a few seconds, so without even accounting for
the force of the wave, the weight of that much water would certainly
crush the bridge. The forces would cause the weight to be unevenly
distrubited with most of the weight landing on the inward side of the
bridge. It would rip that side down and the rest would start falling
appart in reaction to the main damage. The towers and suspension
cables might survive depending on the sideways force exerted upon
them, but the roadway would be toast.


                                 -Walter

>
> Thanks to all who've commented!
>

<lots deleted for brevity>






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