Doppler effect and Shock waves

Doppler effectandShock wavesLecture 10Pre-reading: 16.816.9Please take a clicker and anevaluation formDoppler EffectChange in perceived frequency due to relative motion of a source (S) and listener (L)

Stationary SourceMoving Source

Doppler EffectChange in perceived frequency due to relative motion of a source (S) and listener (L)Case 1: Source at rest, Listener moving fL = (1 + vL/v) fS Case 2: Source and Listener moving

Pay attention to sign of vL, vS ! (positive from L to S)For light wavesfL = [ (cv) / (c+v) ] fS c = 3.0 108 ms1

Doppler EffectChange in perceived frequency due to relative motion of a source (S) and listener (L)Case 1: Source at rest, Listener moving fL = (1 + vL/v) fS Case 2: Source and Listener moving

Pay attention to sign of vL, vS ! (positive from L to S)For light wavesfL = [ (cv) / (c+v) ] fS c = 3.0 108 ms1

Stationary SourceMoving SourceClicker questionsA bird flies in a circle centred on a persons head and emits a continuous sinusoidal sound wave with frequency of f = 1000 Hz.

dNow there is another person standing a large distance away.A bird flies in a circle centred on a persons head and emits a continuous sinusoidal sound wave with frequency of f = 1000 Hz.

Shock WavesWhat if speed of source is equal to or greater than the speed of sound? vS = vsoundvS > vsound

This is exactly analogous to the bow wave produced by a swimmer moving faster than the speed of the waves on water.Bow wave produced by a platypus swimmingShock WavesF/A-18 Hornet

Shock WavesWhat if speed of source is equal to or greater than the speed of sound? vS = vsoundvS > vsound

Shock WavesThe waves pile up at surfaceWhen that surface hits your ears, you hear very loud sound: sonic boomIf vS > v(sound), the surface has the shape of a cone with an opening angle where

vS/v is called the Mach number

The diagram shows the wavefronts generated by an airplane flying past an observer A at a speed greater than that of sound.Clicker questionsThe carillon in the Quad is ringing. You are so excited to have finished your Physics lecture and get to lunch that you run towards the Quad at twice the speed of sound.As you approach the bells, they sound higher pitched than normal lower pitched than normal like a sonic boomThats all, folks!The amount of time Greg spent doing demos was:

A) too longB) a bit longC) just rightD) a bit shortE) too short