1. Nikola Tesla, one of the inventors of radio and an archetypal mad scientist,
ID: 1472463 • Letter: 1
Question
1. Nikola Tesla, one of the inventors of radio and an archetypal mad scientist, told a credulous reporter in 1912 the following story about an application of resonance. He built an electric vibrator that fit in his pocket, and attached it to one of the steel beams of a building that was under construction in New York. Although the article in which he was quoted didn’t say so, he presumably claimed to have tuned it to the resonant frequency of the building. “In a few minutes, I could feel the beam trembling. Gradually the trembling increased in intensity and extended throughout the whole great mass of steel. Finally, the structure began to creak and weave, and the steelworkers came to the ground panic-stricken, believing that there had been an earthquake. ... [If] I had kept on ten minutes more, I could have laid that building flat in the street.” Is this physically plausible?
2. A sound wave that underwent a pressure-inverting reflection would have its compressions converted to expansions and vice versa. How would its energy and frequency compare with those of the original sound? Would it sound any different? What happens if you swap the two wires where they connect to a stereo speaker, resulting in waves that vibrate in the opposite way? Please answer in detail. Thanks
Explanation / Answer
(1)
Definition of Resonance - "The increase in amplitude of oscillation of an electric or mechanical system exposed to a periodic force whose frequency is equal or very close to the natural undamped frequency of the system."
Since, the frequency of the vibrator is same as building's, it will amplify vibrations.
This repition of forces, which caused vibration can fail the buiding's structure by fatigue. The fatigue failure is most common type of failure. One may have to notice, that fatigue strength of a structure is lot less than normal strength.
Fun fact: Army never parade on bridges, as their freiquncy of parade may match frequncy of bridge, which create resonance and may fail the bridge.
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