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For more information, please see full course syllabus of AP Physics B
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Lecture Comments (1)

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Post by Phillip Morton on August 3, 2011

If Obj1 detects obj2 with sonar, determines the distance as 220m with a pulse returning .294s. The returning frequency has increased by 1.32%. Is there a way to determine the speed of obj2 with only this information?

Doppler Effect

  • If either the observer and/or the sound source are moving, the frequency heard by the observer differs from that when both are stationary; this is the Doppler Effect.
  • If the observer and source are stationary, f = v/λ, where v is the speed of sound.
  • Case 1: Observer moves with velocity u toward a stationary source: f’=f (1 + u/v).
  • Case 2: Observer moving with velocity u away a stationary source: f’ = f(1 – u/v).
  • Case 3: Source moving (u) toward a stationary observer: f’ = f / (1 – u/v).
  • Case 4: Source moving (u) away from a stationary observer: f’ = f /(1 + u/v).

Doppler Effect

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Observer Moving, Source Stationary 0:10
    • Observer Intercepts the Wave Front
    • Number of Waves Intercepted
    • Wave Fronts Integrated
    • Towards the Source
    • Moving Away from Source
    • Example: Rain
  • Observer Stationary Source Moving 20:40
    • During Time
    • Wavelength Measured by Observed
  • General Case 33:27
    • Source and Observer Moving
    • Observer is Moving
    • Observer is Stationary
  • Supersonic Speed 43:30
    • Airplane
  • Extra Example 1: Oscillating Spring
  • Extra Example 2: Police Siren
  • Extra Example 3: Sonic Jet