2. Doppler Effect

3. I. Imagine a bug bobbing up and down in the middle of a quiet puddle.

4. Suppose the bug is not going anywhere but is merely treading water in a FIXED position.

5. The crests of the wave it makes are CONCENTRIC circles,

6. because the wave SPEED is the same in all directions.

7. If the bug bobs in the water at a constant FREQUENCY, the distance between wave crests (the λ ) will be the same for all successive waves.

8. Waves encounter point A as FREQUENTLY as point B. BA

9. II. Suppose the jiggling bug moves across the water at a speed LESS than the wave speed.

10. The wave pattern is no longer CONCENTRIC. A B

11. The centers of the circular crests now move in the DIRECTION of the swimming bug.

12. Even though the bug maintains the same bobbing FREQUENCY, an observer at B would encounter the crests more often.

13. AB

14. The observer would encounter a HIGHER frequency.

15. This is because each successive wave crest has a SHORTER distance to travel so they arrive at B more frequently than if the bug were not moving toward B.

16. This change in FREQUENCY due to the motion of the source or receiver sound waves is called the Doppler Effect.

18. The GREATER the speed of the source, the GREATER the Doppler Effect.

19. What is the source? Video taken from a car

20. What is the source?

22. “Physics on the Job”

23. BATS Live for the Doppler Effect!!!

24. People can use the Doppler Effect too http://www.cbsnews.com/stories/2006/09/06/eveningnews/main1977730.sht ml?CMP=ILC-SearchStories http://www.cbsnews.com/stories/2006/09/06/eveningnews/main1977730.sht ml?CMP=ILC-SearchStories

25. III. When the speed of the source in a medium is as GREAT as the speed of the wave it produces, the waves pile up.

27. IV. When the speed of the source in a medium is GREATER than the speed of the wave it produces, the source “breaks through” the wave barrier.

29. An F/A-18 Hornet passing through the sound barrier. The water vapor, density and temperature was just right and there just happened to be a camera in the vicinity to capture the moment. Navy Ensign John Gay made this phenomenal photograph on July 7, 1999 while aboard the carrier USS Constallation as Navy Lt. Ron Candiloro flew by.

31. http://faculty.rmwc.edu/tmichalik/movies/F-18.MPEG

32. Break the Barrier!!! The bullwhip or stock whip moves faster than sound. The tip of the whip breaks the sound barrier and causes a sharp crack. The sound barrier was first broken in a vehicle on land in 1948 by a rocket-powered test vehicle at Muroc Air Force Base (now Edwards AFB) in CA. Chuck Yeager was the first person to break the sound barrier in level flight on October 14, 1947 while flying the experimental Bell X-1 at Mach 1. Mach is a ratio of the speed to the speed of sound (i.e. Mach 2 is twice the speed of sound) http://en.wikipedia.org/wiki/Sound_barrier#Media

33. This picture shows a sonic boom created by the THRUST SSC team car as it broke the land speed record (and also broke the sound barrier on land).

34. Something which travels faster than the speed of sound is said to be SUPERSONIC.

35. This figure shows a bullet travelling at Mach 2.45. The mach cone and shock wavefronts are very noticeable.

36. When the CONICAL shell of compressed air that sweeps behind a supersonic aircraft reaches listeners on the ground below, the sharp crack they hear is described as a SONIC BOOM.

37. The Doppler Effect is the apparent change in FREQUENCY from a source which could be visible light.

38. If the source moves towards the observer, the waves will appear closer together forming shorter WAVELENGTHS. This is referred to as a BLUE shift since the wavelengths are becoming shorter.

39. On the other hand, if the source is moving away from the observer, the waves will appear stretched out to longer WAVELENGTHS. This is referred to as a RED shift since the wavelengths are becoming longer.

40. Red light Blue light

41. Use of the Doppler shift in astronomy Here is what the spectrum of a star that is moving toward us might look like (somewhat simplified):

42. Here is what the spectrum of a star that is moving away from us might look like (somewhat simplified):

43. How it is used in Weather

45. A. What does it mean when an astronomer reports a galaxy as red-shifted? A red-shifted galaxy implies that the galaxy is moving away from us, resulting in longer wavelengths and lower frequencies of light emitted by the galaxy.

46. The local Astronomy club wants to create a T-shirt which demonstrates the Doppler Effect. What colors should the front and back be? FRONTBACK