Doppler Effect ((new)) -

Police use Doppler radar to bounce radio waves off your car. By measuring the change in frequency of the returning wave, they can calculate your exact speed.

At its core, the Doppler Effect is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. doppler effect

It was first proposed by Austrian physicist in 1842. He hypothesized that the observed frequency of light and sound waves depends on the relative speed of the source and the observer. How It Works: The "Accordion" Principle Police use Doppler radar to bounce radio waves off your car

When an object moves away from Earth, its light waves stretch out, shifting toward the red end of the spectrum (longer wavelengths). It was first proposed by Austrian physicist in 1842

used this phenomenon to discover that almost every distant galaxy is "redshifted." This provided the first concrete evidence that the universe is expanding. Real-World Applications