Lecture 10 Doppler effect and Shock waves Prereading
- Slides: 23
Lecture 10 Doppler effect and Shock waves Pre-reading: § 16. 8– 16. 9 Please take a clicker and an evaluation form
Doppler Effect • Change in perceived frequency due to relative motion of a source (S) and listener (L) Stationary Source Moving Source
Doppler Effect • Change in perceived frequency due to relative motion of a source (S) and listener (L) • Case 1: Source at rest, Listener moving f. L = (1 + v. L/v) × f. S • Case 2: Source and Listener moving • Pay attention to sign of v. L, v. S ! (positive from L to S) • For light waves f. L = √[ (c–v) / (c+v) ] × f. S c = 3. 0 × 8 10 – 1 ms
Doppler Effect • Change in perceived frequency due to relative motion of a source (S) and listener (L) • Case 1: Source at rest, Listener moving f. L = (1 + v. L/v) × f. S • Case 2: Source and Listener moving • Pay attention to sign of v. L, v. S ! (positive from L to S) • For light waves f. L = √[ (c–v) / (c+v) ] × f. S c = 3. 0 × 8 10 – 1 ms
Stationary Source Moving Source
Clicker questions A bird flies in a circle centred on a person’s head and emits a continuous sinusoidal sound wave with frequency of f = 1000 Hz.
d A bird flies in a circle centred on a person’s head and emits a continuous sinusoidal sound wave with frequency of f = 1000 Hz. Now there is another person standing a large distance away.
Shock Waves What if speed of source is equal to or greater than the speed of sound? v. S = vsound v. S > 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 swimming
Shock Waves F/A-18 “Hornet”
Shock Waves What if speed of source is equal to or greater than the speed of sound? v. S = vsound v. S > vsound
Shock Waves The waves ‘pile up’ at surface When that surface hits your ears, you hear very loud sound: sonic boom • If v. S > v(sound), the surface has the shape of a cone with an opening angle α where v. S/v is called the Mach number
Clicker questions The diagram shows the wavefronts generated by an airplane flying past an observer A at a speed greater than that of sound.
The 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 1. higher pitched than normal 2. lower pitched than normal 3. like a sonic boom
That’s all, folks!
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