Experiments

Is it possible to build an earthquake machine?

posted: 04/11/12
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As seen in "MythBusters: Earthquake Machine."
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Finding: BUSTED

Explanation: Engineering genius Nikola Tesla figured out how to do a lot of impressive stuff like harness electricity and get cars to crank up. But did he really create a small mechanical generator that could produce earthquakes on demand? MythBusters Adam Savage and Jamie Hyneman aren't so sure.

Tesla invented a machine consisting of pistons and air springs that turns a central linear rod. He claimed that, when attached to objects, this device could send vibrations through them at the precise frequency needed to literally shake them apart in much the same way an earthquake would. In physics terms, the earthquake machine supposedly could match an object's resonant frequency, or the vibration speed that naturally accelerates its oscillation rate.

To understand how resonant frequency works, think about a playground swing. The energy someone gets from a push varies depending on the frequency and location of said push. When you push at the right moment of resonant frequency, the swing moves farther and higher. If Tesla's theory was correct, as his machine increases an object's oscillation rate, the resulting positive feedback should cause the object to break apart.

To see if Tesla was all talk, the MythBusters rebuilt the earthquake machine using an electromagnetic linear motor. They then attached the 5-pound device to a bridge and adjusted the frequency of the motor's linear revolutions to match the structure's resonant frequency.

Amazingly, that did send a detectable vibration through the bridge — one that could be felt even hundreds of feet away from the oscillating motor. But while those results confirmed Tesla's theory was on the right track, the machine wasn't capable of inciting earth-shaking damage.

The 19th-century savant still has a ton of impressive inventions credited to his name; however, the quake box is one that doesn't live up to the hype.

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