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What Is The Doppler Effect, What Does It Do For Us?

Image Credit: Wikimedia

We’ve all heard how the siren changes as the ambulance passes by us at speed. The curtain of an approaching siren rises, and also falls as the vehicle drives away. This change in tone of sound is called the doppler effect, or Doppler shift, after the mathematician and astronomer Christian Doppler, who discovered it in 1842.

The Doppler effect is caused by overlapping sound waves or opening them up. It determines the pitch of the sound you hear, the frequency of the sound, or how many waves per second. The siren’s frequency does not change, but as the ambulance approaches you, the same number of waves are stuck in a gradually shrinking range. This, in turn, increases the frequency of the sound waves you hear, so the pitch of the sound is higher (i.e. high). As the ambulance moves away, the sound waves spread over an increasing distance, the frequency and therefore the pitch of the sound also drops (the sound becomes pesky).

Let’s design an experiment to better understand the Doppler effect. Every 3 seconds from a car approaching you, you get a ball thrown towards you. As the car approaches you, the time the balls arrive at you will be slightly shorter, because the time the ball spends in the air will be reduced, as each new shot will be made closer than the previous one. Therefore, the arrival intervals of the balls will be narrowed according to the person who catches the ball.

In the same format, when the car starts to move away, each ball will spend more time in the air than the previous one, as the arrival range of the balls increases. Therefore, the time intervals of the balls will increase.

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The Doppler effect is observed in objects moving relative to each other. If you were the one who threw the ball in the advancing car, the range of shots of the ball would, of course, be equal for you. Let’s not call me a doppler effect. There are many methods in which this effect is actually used in our daily lives.

Speed Measurement Using Doppler Effect

The area where the Doppler effect is most beneficial in daily life is the determination of the speed of motion. If the properties of the wave emitted from the source and observed are known, it can be calculated at what speed the source and Observer move relative to each other. Measuring vehicle speeds, for example
Doppler effect is used in the radars used for. Waves emitted from the radar hit the moving vehicle and return. The speed of the vehicle is calculated by looking at the difference between the frequency of the emitted waves and the frequency of the returning waves. In medicine, this effect is again used to measure the blood flow rate.

Measuring The Distance Of Planets

The Doppler effect, which applies to all kinds of wave types regardless of sound, light, electromagnetic, is also actively used in astronomical calculations. In order to calculate the speed at which a celestial body approaches or distances itself from Earth, light reaching Earth from that body is analyzed. By comparing the spectrum of light emitted on earth from atoms in the celestial body with the spectrum of light emitted on Earth from atoms, the speed of the celestial body relative to the Earth is calculated.

Light deflection and relativistic doppler effect. Image Credit: Wikimedia

Although Doppler predicted that his invention would be useful to future generations, he probably couldn’t think of that much himself.

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