The document discusses the Doppler effect, where the observed frequency of a wave depends on the relative motion between the observer and the source. It notes that a train horn will be higher pitched as a train approaches and lower pitched as it moves away, due to the Doppler effect. It provides examples of this occurring with both trains and cars. The document explains that the Doppler effect is caused by the observer and source moving relative to each other, resulting in a different observed frequency than what is emitted. It also lists the three scenarios that can cause the Doppler effect: a stationary source with a moving receiver, a stationary receiver with a moving source, and both the source and receiver in motion. Finally, it introduces the Doppler effect formula and poses sample

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