The Sky Is My Garden: Resonance

Sunday, September 13, 2020

Resonance

So, there is a weird thing at my house. I can tell when the big brown UPS van is approaching from quarter-mile away. Long before I see it.

Keep this thought in mind.

Nikola Tesla, the brilliant Serbian inventor who gave us (or perfected) the electrified world we now share, was very interested in harmonic resonance frequencies. You are likely familiar with these. An example is when sound shatters a glass. The frequency of soundwaves, upon reaching resonance, cause the glass to vibrate so violently the glass shatters.

According to Merriam-Webster, resonance is “a vibration of large amplitude in a mechanical or electrical system caused by a relatively small periodic stimulus of the same or nearly the same period as the natural vibration period of the system.”

Tesla tinkered with resonance frequencies in electrical circuits and mechanical oscillators. He claimed that a mechanical oscillator he made could destroy the Empire State Building with "five pounds of air pressure" if attached on a girder and tuned to the proper frequency.

Maybe absurd.

But consider the story of the Tacoma Narrows Bridge. The bridge was nicknamed “Galloping Gertie” due to the way its deck swayed under certain wind conditions. In 1940, only four months after being opened to traffic, wind at a certain speed caused the bridge deck to oscillate (something called aeroelastic flutter) at a forced resonance. The bridge quite literally tore itself apart. I have posted a short video about the bridge at the end of this blog.

Now, back to the UPS rig.

Something about the elevation of my house relative to the road, the open prairie before me carrying the sound waves, and the bullying rumble of the UPS van allows the sound waves to, more or less, assault my house from a great distance. The van produces sound waveforms that force my windows to, for lack of a more precise word, pulse rapidly. My entire house fills with a low but very perceptible rumble.