The Surprisingly Simple Physics of the Doppler Effect

You have probably experienced the Doppler Effect even if you didn't know what to call it at the time.
Loukia Papadopoulos

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The Doppler Effect, also known as the Doppler Shift, is named after the Austrian physicist Christian Doppler, who coined the hypothesis back in 1842. When explained, it seems simple and self-evident. 

It is, however, nonetheless a crucial concept. Let's explain it, shall we? One of the best ways to do so is with the example of an oncoming ambulance. When an ambulance approaches you, its siren has a higher pitch as it is approaching than when it is moving away. That's simply the Doppler Effect.

The principle was tested in 1845 by Dutch chemist and meteorologist Buys Ballot using sound waves. He found that a sound's pitch was higher than the emitted frequency when the sound source approached an observer and lower than the emitted frequency when the sound source moved farther away from the observer.

It was finally proved in 1848 by an experimental study undertaken by Scottish civil engineer, naval architect and shipbuilder John Scott Russell. Today, the Doppler effect has applications in robotics, in some types of radar, and even in astronomy.

It is is most prominently used to calculate the speed at which planets, stars, and galaxies are approaching or receding from us and to find new alien worlds.

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