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Imagine your self hanging near the top of a flagpole. If you rock back and forth at just the right speed and increase speed slowly. eventually the pole will bend and then snap.
Take the same idea but instead of yourself at the top of the pole, there is something that looks like a metronome. It starts
rocking with less force and gradually makes it bend further and further until it makes it snap.
it could be used by demolition crews as a tool to bring down large structures without the use of heavy machinery or explosives.
Stump Shaker
Stump_20Shaker
The same tyrannical principle. [bungston, Dec 11 2008]
Tesla's earthquake machine
http://en.wikipedia...echanical_resonance
Either baked by Tesla or busted by Adam and Jamie. [Gamma48, May 02 2009]
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Annotation:
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Many buildings are specifically designed to prevent this to
prevent earthquake damage.
Even if they weren't finding the resonant frequency of a
building, finding an attachment point (or even
combination of points) where said resonance can be
applied (it doesn't do any good if your attachment point
fails before your building does), and maintaing resonant
excitation once the building starts swaying are all non
trivial problems.
Also, in a related note to the attachment point, I would
expect most buildings to have a non-catastrophic failure
mode wherein parts of the building broke and altered the
resonant frequency sufficiently to prevent total failure.
Finally, one of the major advantages of explosives or
machinery is that they allow you to control the failure.
The mostly do this be applying overwhelming force to
guarantee failure in the desired spot. A shaking or swaying
building would fail at exactly it's critical load, and since
there is no way to know this exactly (building materials are
not uniform), there is also no way to determine where the
building is going when it comes down.. |
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//it could be used by demolition crews as a tool to bring down large structures without the use of heavy machinery or explosives.// |
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And not just one building, but all of them down the street. Like a row of dominoes. |
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/I would expect most buildings to have a non-catastrophic failure mode/ |
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Such modes would be prohibited as part of the building code. |
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[-] bad science. the metronome device you propose would be heavier than the //heavy machinery// currently used for the purpose because physical structures are damped to some degree at all frequencies. |
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If a building was an ideal spring, you could excite it at its resonant frequency with your metronome device, and the oscillations would grow indefinitely. For a real building (or damped spring), the oscillations get bigger until the energy going in (from your metronome) equals the energy going out (from the dampers). A flagpole is very springy with little damping, but damping (provided by the ground around the flagpole, air resistance, etc) still slows down the pole and makes it pretty hard to bring down. For a real building, with lots of different materials, the energy required to get any meaningful oscillation is much greater. You'd need a wrecking-ball-crane-sized machine on the top of the building, moving really forcefully, to bring down the building. A normal wrecking ball crane would be cheaper and more effective. |
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Although Mythbusters seemed to refute the efficacy of Tesla's oscillator, especially for modern structures, I still believe the idea is essentially valid. |
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