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Vibrations and Waves

Vibrations and Waves. the basis of sound and light. Pendulum. Back and forth motion of pendulum called simple harmonic motion (SHM) Period is time it takes to swing back and forth. Displacement is how far the pendulum moves from the centerline Period is dependent on string length

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Vibrations and Waves

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  1. Vibrations and Waves the basis of sound and light

  2. Pendulum • Back and forth motion of pendulum called simple harmonic motion (SHM) • Period is time it takes to swing back and forth. • Displacement is how far the pendulum moves from the centerline • Period is dependent on string length • Period is independent of weight • Period is independent of displacement

  3. Wave motion • Pendulum demonstrates the back and forth repetitive motion of a wave. • There are water waves, light waves, sound waves, and many more types of waves. • Waves move energy without a net movement of matter.

  4. Source of Energy for Waves • Waves get their energy from vibration. • The back and forth motion of vibration causes the particles in the medium (water for an ocean) to move also resulting in wave motion.

  5. Amplitude • Measure of strength of wave • distance from midpoint to crest or trough

  6. Wavelength • distance between one crest and the next •  is the symbol for wavelength

  7. Frequency • describes movement of wave • number of vibrations per second • measured in hertz • period is time to make one complete cycle • frequency = 1 / period • period = 1 / frequency

  8. Wave Speed • Distance between crests • Divided by the time between the crests • wave speed = frequency x wavelength • v = f 

  9. Relationship between frequency and wavelength for sound in air

  10. Transverse Waves • Sine wave • motion of wave at right angles to movement of wave http://www.control.co.kr/java1/wave%20Trans/WaveTrans.html

  11. Longitudinal Wave • particles move back and forth in direction of the movement of the wave

  12. Superposition • When two waves occupy the same space, their amplitudes add together • The waves pass through each other • After their combination, they continue along their original path as if they had not combined for the moment. http://www2.biglobe.ne.jp/~norimari/science/JavaEd/e-wave2.html

  13. Constructive Interference

  14. Destructive Interference http://www2.biglobe.ne.jp/~norimari/science/JavaEd/e-wave3.html

  15. Standing Waves • Reflection combines with incoming wave to produce portions of the wave that appear to be stationary • nodes are stationary • antinodes move the most http://www.physicsclassroom.com/mmedia/waves/swf.html

  16. Doppler effect • if the wave generator is moving, the apparent frequency of the wave changes to a stationary observer • higher frequency as the center of the wave comes to you • lower frequency as the center of the wave moves away

  17. Doppler effect • car horn • sirens • radar gun • light • increase frequency – blue shift • decrease frequency – red shift http://www.shep.net/physics/

  18. Bow Waves • waves travel in all directions from the source of the wave (sound) • if the source of the sound is moving slower than the wave, the Doppler effect is created • higher frequency as sound approaches • lower frequency as sound moves away http://www.astro.ubc.ca/~scharein/a311/Sim/doppler/Doppler.html

  19. Stationary Source

  20. Moving slower than wave speed

  21. Object same speed as wave

  22. Object faster than speed of wave

  23. Sonic Boom • Hear the movement of air not the sound from the object • Sonic boom formed all the time the object moves faster than the speed of the wave not just as it reaches the speed of the wave • Object does not have to make a sound to form a sonic boom • snapping towel

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