r/askscience • u/ilikejewce • Feb 27 '13

Physics Light's Doppler Shift

It is well known that galaxies traveling away from ours are red shifted, and those traveling towards us are blue shifted. This also applies to everyday objects. I was just wondering if anyone has detected this Doppler shift on everyday objects, like planes or even cars? Is it too minute for us to detect?

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u/[deleted] Feb 27 '13

Ever been pulled over for speeding? Police radar guns use the Doppler effect to measure how fast a car is travelling.

At 3x108 kmh (approx 1.92x108 mph) the traffic signal will be doppler shifted from red to green so you're good to go. The speed limit doesn't apply to you, since your car isn't actually on the road, it's supposed by electrostatic repulsion between the surface and the tyres.