Doppler's effect lo5

1. DOPPLER'S EFFECT
PHYS 101 LO5

2. 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.

3. 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!!

4. Why does Doppler's effect
occur?
• Click here for a passing car horn
You are
here as the
car
approaches
↑
This is the car.

5. Why does Doppler's effect
occur?
• Click here for a passing car horn
You are
here as the
car
approaches
↑
This is the car.

6. Why does Doppler's effect
occur?
This is the car.
You are
here as the
car leaves

7. 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).

8. Three scenarios
• stationary source, moving receiver
• stationary receiver, moving source
• moving source and receiver

9. Three scenarios
• stationary source, moving receiver
• stationary receiver, moving source
• moving source and receiver
All can be concluded in one formula

10. • fr and fs: frequency of receiver and source
• vr and vs: speed of receiver and sourcer
• v: speed of sound in air

11. 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?

12. solution

13. • What if the plane is leaving?

14. • What if the plane is leaving?

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