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Doppler effect

Can you measure a speed using the Doppler effect?

Nivel :

High School



In this protocol, the student uses a sound recording of a moving vehicle to calculate its speed by measuring the Doppler effect. The recording is present in the Sounds Library of the application.

➡️ Retrouve cette activité dans le Catalogue d'activités de l'application FizziQ
(Activités > ➕ > Catalogue d'activités)

En savoir plus

1. You have probably noticed that the noise of a car is higher when it comes towards you than when it moves away from you. This is the Doppler effect. Can we calculate using this effect the speed of a vehicle from the noise it creates?

2. For this experiment we need the recording of a sound emitted by a moving mobile, for example the honking of a car when it passes in front of you.

3. You can create this recording yourself, but in the meantime you can use a recording that is in the sound library in the Tools tab.

4. Listen to the recording called Doppler Effect. What do you see? Can you explain this phenomenon theoretically?

5. Records and compares the sound spectrum of the horn before and after the car has passed the observer. Do you notice a difference in the frequency of the peaks?

6. Calculate this percentage offset of the frequency value for multiple frequency peaks? Can you deduce the speed of the car?

7. We would like to make more precise measurement, can you use the sound signal amplitude measurement to calculate the car speed more accurately?

8. Document your results in your logbook. Is the vehicle a car or a bicycle?

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