DOPPLER'S EFFECTPHYS 101 LO5

Real Life Experience

• You must have noticed this before. As the train approaches the station, the sound of its horn at a higher pitch and as the train moved away, it is at a lower pitch.

Real Life Experience

• You must have noticed this before. As a train or a car approaches, the sound of its horn is at a higher pitch and as it moves away, the horn is at a lower pitch. (high pitch reflects high frequency)

This is Doppler's effect!!

Why does Doppler's effect occur?

• Click here for a passing car horn

You are here as the car approaches

↑

This is the car.

Why does Doppler's effect occur?

• Click here for a passing car horn

You are here as the car approaches

↑

This is the car.

Why does Doppler's effect occur?

This is the car.

You are here as the car leaves

Why does Doppler's effect occur?

• The Doppler effect occurs when a source of waves and the observer are moving relative to each other, resulting in the observer measuring a different frequency of the waves than the frequency that the source is emitting.

• The phenommenon is named for the Austrian physicist Christian Doppler (who first described it).

Three scenarios

• stationary source, moving receiver

• stationary receiver, moving source

• moving source and receiver

Three scenarios

• stationary source, moving receiver

• stationary receiver, moving source

• moving source and receiver

All can be concluded in one formula

• fr and fs: frequency of receiver and source

• vr and vs: speed of receiver and sourcer

• v: speed of sound in air

Questions

Assume you are Sitting on a beach one day. You find a flight is moving towords you with speed of 100m/s. What frequency will you hear as the plane flying towards you which engine emiting sound with a frequency of 1000 Hz?

solution

• What if the plane is leaving?

• What if the plane is leaving?

Resources

• http://www.physicsclassroom.com/class/sound/Lesson-3/The-Doppler-Effect-and-Shock-Waves