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I’m a nerd who loves engineering and often I’ll be reading something, and a concept will resonate with me. And so, I’ve been thinking about the word 'resonance' itself.

It’s a term we often use in engineering and understand intuitively, but perhaps not always fully.

Resonance determines the length of antenna, why bridges collapse, and why a Les Paul guitar sounds so good. So what is it precisely?

Every object has a frequency or pitch at which it will vibrate sympathetically. At that particular pitch, the vibrations will increase hugely.
Ella Fitzgerald would famously break wine glasses by singing at the resonant frequency of the glass such that it would explode. Memorex (Cassette Tapes) famously built adverts around doing the same thing with her recorded voice.

The Tacoma narrows bridge collapse occurred when the wind passing through it happened to reach the resonant frequency of the bridge. The swinging peaked at resonance and moved so much that it fell apart.

View the video here
Tacoma 300px
eight col aasdaSmbulance generic If you look at users of radio-telephones (RT’s) such as taxis, police and ambulance you’ll probably notice that the length of the antennae are quite similar. Why is that?
If you think about it, we live in a sea of radio waves; FM radio, television, RT’s, cellular etc ad infinitum. How does an antenna preferentially pick up the signal we want?
A radio antenna for the emergency services band (143 MHz) will be resonant at about 500mm long and will have a sensitivity graph like the diagram below.
The antenna is effectively a filter that is very, very sensitive at 1 frequency.  A tiny voltage will appear on the antenna, but the highest voltage will be at the resonant frequency.
3db bandwidth

Mechanically, if you’ve towed a caravan or pushed a kid on a swing, you may have experienced resonance.  A small push keeping the swing moving at its resonant frequency.


Watch this frightening video of caravan resonance here
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