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Chapter 19 Vibrations & Waves

Part IV: Sound. Chapter 19 Vibrations & Waves. Oscillating motion of a mass on a spring. Vibrations. Vibrations are a common phenomenon. Period. Time required for a full oscillation (one round trip) is called the period of oscillation.

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Chapter 19 Vibrations & Waves

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  1. Part IV: Sound Chapter 19Vibrations & Waves Physics 1 (Garcia) SJSU

  2. Oscillating motion of a mass on a spring Vibrations Vibrations are a common phenomenon. Physics 1 (Garcia) SJSU

  3. Period Time required for a full oscillation (one round trip) is called the period of oscillation. Pendulum that is about one meter long has a period of two seconds per oscillation. Note: Measure the period of a pendulum in lab. Physics 1 (Garcia) SJSU

  4. Frequency Frequency is the inverse of the period, (Frequency) = For example, for a period of 2 seconds per oscillation, the frequency is ½ oscillation per second or ½ Hertz. 1 Hertz = 1 oscillation per second 1 (Period) Physics 1 (Garcia) SJSU

  5. Amplitude The distance from the rest position is the amplitude of oscillation. Amplitude

  6. Waves Concept of vibrations extends into the phenomenon of wave motion. String Sound Water waves Radio Light waves Physics 1 (Garcia) SJSU

  7. Transverse Waves For transverse waves the wave’s amplitude is perpendicular to the wave’s motion. Amplitude Wave Motion Amplitude Physics 1 (Garcia) SJSU

  8. Doing “The Wave” Synchronized standing and sitting by a stadium’s crowd is an example of a transverse wave. Video analysis indicates that it takes only a few dozen fans leaping to their feet with their arms up to trigger a wave. Once started, it usually rolls in a clockwise direction at a rate of about 40 feet per second, or about 20 seats per second. At any given time, the wave pulse is about 15 seats wide. Physics 1 (Garcia) SJSU

  9. Longitudinal Waves For longitudinal waves, amplitude and wave motion are parallel. Wave Motion Amplitude Amplitude A crowd can do a longitudinal wave by moving side-to-side instead of up-and-down Physics 1 (Garcia) SJSU

  10. Wavelength Wavelength is distance between crests or between troughs of waves. Longitudinal Transverse Physics 1 (Garcia) SJSU

  11. Wave Speed The speed at which waves travel is called the wave speed. Speed of sound = 330 m/s = 725 mi/hr Speed of light = 300,000,000 m/s Water waves at the beach move a few miles per hour Physics 1 (Garcia) SJSU

  12. Tsunami Waves Tsunamis are ordinary water waves, just like waves in your bathtub, but because they are typically generated by deep sea earthquakes they carry huge amounts of energy and momentum, traveling at almost 500 mph while in the deep ocean. The tsunami of 26 December 26th 2004 was produced by an earthquake whose epicenter was located off the coast of Indonesia in the Indian Ocean. The death toll is estimated at over a quarter of a million persons. Animation by Vasily V. Titov Physics 1 (Garcia) SJSU

  13. Wave Relations Wave speed, wavelength & frequency related. (Wave speed) = (Wavelength) x (Frequency) (Wave length) = (Frequency) = (Wave speed) (Frequency) (Wave speed) (Wavelength) Physics 1 (Garcia) SJSU

  14. Check Yourself What is the wave length? What is the wave speed? What is the wave’s frequency? What is the wave’s period? 2 m 6 m/s Physics 1 (Garcia) SJSU

  15. Demo: Hearing Sound Range of human hearing is roughly 20 Hertz to 20,000 Hertz. Wave speed for sound is 330 m/s Wavelength of 20 Hertz is 16 m (about 50 ft) Wavelength of 20,000 Hz is 1.6 cm (½ inch) Physics 1 (Garcia) SJSU

  16. Hearing in Animals Frequency range varies widely, depending on natural adaptation using sound to communicate, locate food, avoid predators, etc.

  17. Constructive Interference Two waves in phase add together, which is called constructive interference. Physics 1 (Garcia) SJSU

  18. Destructive Interference Two waves out of phase cancel each other out, which is destructive interference. Physics 1 (Garcia) SJSU

  19. In & Out of Phase

  20. Demo: In & Out of Phase Pair of speakers constructively interfere when they are in phase (oscillating together). When out of phase (reverse wires on one of the speakers) then they destructively interfere. Out of Phase Physics 1 (Garcia) SJSU

  21. Noise-Canceling Headphones Noise-canceling headphones use a microphone that listens for noise and a speaker that produces the same noise but out of phase (cancellation by destructive interference) External Noise Canceling Sound

  22. Demo: Speaker Baffle Why are speakers mounted behind a baffle and inside an enclosure? Physics 1 (Garcia) SJSU

  23. Standing Waves When a wave interferes with its reflection, this may create a standing wave.

  24. Standing Waves and Phase Standing waves are another example of constructive and destructive interference. Physics 1 (Garcia) SJSU

  25. Doppler Effect Sound coming from a moving object has a different wavelength and frequency than if it were stationary. If moving towards you, wavelength shorter and frequency higher. If moving away, wavelength longer and frequency lower. Physics 1 (Garcia) SJSU

  26. Demo: Doppler Shift Hear frequency as higher when buzzer is moving towards you and hear it as lower when moving away from you. Shorter Wavelength Higher Frequency Lower Frequency Longer Wavelength Physics 1 (Garcia) SJSU

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