Ep. 165: Doppler Effect

You know how a police siren changes sound when it passes by you? That's the doppler effect. It works for sound waves and it works for light waves. Astronomers use the doppler effect to study the motion of objects across the Universe, from nearby extrasolar planets to the expansion of distant galaxies. Doppler shift is the change in length of a wave (light, sound, etc.) due to the relative motion of source and receiver. Things moving toward you have their wavelengths shortened. Things moving away have their emitted wavelengths lengthened.

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2 Responses to “Ep. 165: Doppler Effect”

1. Mike Cloutier says:

   December 17, 2009 at 2:45 pm

   Hello. That was an interesting point about the Doppler shift being discovered in the examination of light, not sound, because there wouldn't have been anything like a car (train, maybe) to observe the phenomenon.

   But, a Doppler shift can be observed in horse racing. Each hoof in a 10-horse race, for example, generates a sound pulse creating an uneven low-frequency but audible and continuous tone that is raised in pitch as the horses approach and lowered after they pass and recede. I estimate the difference would be a semi tone, and noticeable if you pay attention to it and you stand right beside the rail.

   You can also notice the individual hoof beats of a single horse or a a few in a smaller race become discernibly slower as they pass, but that's not Doppler shift . . . is it?

   Imagine an entire cavalry advance coming toward you . . .
2. Stephen Krisocki says:

   December 30, 2009 at 9:05 pm

   The earth rotates at 1600 kilometers per second? The earth would disintegrate if its day lasted only 25 seconds. You mean 1600 kilometers per HOUR. Otherwise, it's a great podcast. Thanks

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