1. Physics 11 n Waves 6 – Doppler Effect

2. Constructive & Destructive Interference:

3. When waves meet:

4. Standing Waves:

5. Waves and Wave Length: n The standing wave to the left represents one half of the wavelength of the wave or ½. n This would be a complete wave cycle or 2/2 or 1. n This would be 3/2 or 1 ½ wave.

6. Fundamental Frequencies:

7. Interference is a characteristic of all waves.

8. Standing Waves n n When two sets of waves of equal amplitude and wavelength pass through each other in opposite directions, it is possible to create an interference pattern that looks like a wave that is “standing still.” It is a changing interference pattern. n Demo - Rope and strobe n Demo - Mechanical overhead model

9. Visible Spectrum:

10. θ Sonic boom manifested by condensation of water in air Sonic Boom: sin  = v sound /v source = 1/“Mach number”

11. Sonic boom of bullet in flight (holographic interferometry?) Sonic Boom: n How fast is the bullet traveling?  Mach # = 1/sin 

12. Super Sonic Flight: n http://stokes.byu.edu/teaching _resources/boom_script_flash.html http://stokes.byu.edu/teaching _resources/boom_script_flash.html http://stokes.byu.edu/teaching _resources/boom_script_flash.html

13. DOPPLER EFFECT n n Refers to the change in frequency when there is relative motion between an observer of waves and the source of the waves n Doppler Movie - URL URL n Doppler Movie - URL URL

14. When a source of waves and an observer of waves are getting closer together, the observer of the waves “sees” a frequency for the waves that is higher than the emitted frequency. When a source of waves and an observer of waves are getting farther apart, the observer of the waves “sees” a frequency for the waves that is lower than the emitted frequency.

15. n All waves exhibit the Doppler effect. n n A particularly interesting example is used by astronomers to determine if light emitting objects (such as stars) are getting closer to us or farther away. n n On average most stars are moving farther away, and their light spectra are “red shifted.”

17. Red Shift: Moving Away from source Actual Visual Spectrum Observed Visual Spectrum

18. Blue Shift: Moving towards source Actual Visual Spectrum Observed Visual Spectrum

20. n Radar bounced off a spinning planet can exhibit a Doppler effect and lead to a determination of the spin rate of the planet. n This was used to discover that Venus has a retrograde spin. n Of course police use the Doppler effect to catch speeding motorists.

23. BOW WAVES n n Waves in front of moving object pile up. n n The familiar bow wave generated by a speedboat knifing through the water n n It is a non-periodic wave produced by the overlapping of many periodic circular waves. It has a constant shape.

26. Video Demonstration: n Demo 2.1 – Waves & Wake from Phys123

27. SHOCK WAVES n n Just as circular waves move out from a swimming bug, spherical waves move out from a flying object. If the object flies faster than the waves, the result is a cone-shaped shock wave. n n There are two booms, one from the front of the flying object and one from the back.

28. Video Demonstrations:

29. - slower than the speed of sound n Subsonic n Supersonic - faster than the speed of sound n n Mach Number = speed of sound speed of object