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Vibrations and Waves

Vibrations and Waves. A motion that repeats itself in constant time intervals is called periodic. Harmonic Motion. - vibratory, periodic motion is called harmonic because of its relationship to sound and harmony. Cycle Period Frequency. Longer Pendulums Have longer Periods.

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Vibrations and Waves

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  1. Vibrations and Waves

  2. A motion that repeats itself in constant time intervals is called periodic.

  3. Harmonic Motion • - vibratory, periodic motion • is called harmonic because of its relationship to sound and harmony Cycle Period Frequency

  4. Longer Pendulums Have longer Periods.

  5. Vibrations of a Pendulum CHECK YOUR NEIGHBOR A 1-meter-long pendulum has a bob with a mass of 1 kg. Suppose that the bob is now replaced with a different bob of mass 2 kg, how will the period of the pendulum change? A. It will double. • It will halve. • It will remain the same. • There is not enough information.

  6. Vibrations of a Pendulum CHECK YOUR ANSWER A 1-meter-long pendulum has a bob with a mass of 1 kg. Suppose that the bob is now replaced with a different bob of mass 2 kg, how will the period of the pendulum change? A. It will double. • It will halve. • It will remain the same. • There is not enough information. Explanation:The period of a pendulum depends only on the length of the pendulum, not on the mass. So changing the mass will not change the period of the pendulum.

  7. Vibrations of a Pendulum CHECK YOUR NEIGHBOR A 1-meter-long pendulum has a bob with a mass of 1 kg. Suppose that the bob is now tied to a different string so that the length of the pendulum is now 2 m. How will the period of the pendulum change? A. It will increase. • It will decrease. • It will remain the same. • There is not enough information.

  8. Vibrations of a Pendulum CHECK YOUR ANSWER A 1-meter-long pendulum has a bob with a mass of 1 kg. Suppose that the bob is now tied to a different string so that the length of the pendulum is now 2 m. How will the period of the pendulum change? A. It will increase. • It will decrease. • It will remain the same. • There is not enough information. Explanation:The period of a pendulum increases with the length of the pendulum.

  9. Frank Oppenheimer demonstrates that a swinging pendulum bob traces a sine curve on a uniformly moving conveyor belt.

  10. Describing a Wave • Crests • Troughs Frequency Period

  11. Wave Motion Wave speed • how fast a disturbance moves through a medium • related to the frequency and wavelength of a wave Example: • a wave with wavelength 1 meter and frequency of 1 Hz has a speed of 1 m/s

  12. Transverse and Longitudinal Waves • Longitudinal wave - wave particles vibrate back • and forth along the path that the wave travels.

  13. Transverse and Longitudinal Waves • Transverse wave - wave particles vibrate back and forth perpendicular to the path that the wave travels.

  14. Transverse Waves CHECK YOUR NEIGHBOR The distance between adjacent peaks in the direction of travel for a transverse wave is its A. frequency. • period. • wavelength. • amplitude.

  15. Transverse Waves CHECK YOUR ANSWER The distance between adjacent peaks in the direction of travel for a transverse wave is its A. frequency. • period. • wavelength. • amplitude. Explanation: The wavelength of a transverse wave is also the distance between adjacent troughs, or between any adjacent identical parts of the waveform.

  16. Transverse Waves CHECK YOUR NEIGHBOR The vibrations along a transverse wave move in a direction A. along the wave. • perpendicular to the wave. • Both A and B. • Neither A nor B.

  17. Transverse Waves CHECK YOUR ANSWER The vibrations along a transverse wave move in a direction A. along the wave. • perpendicular to the wave. • Both A and B. • Neither A nor B. Comment: The vibrations in a longitudinal wave, in contrast, are along (or parallel to) the direction of wave travel.

  18. Transverse Waves CHECK YOUR NEIGHBOR The distance between adjacent peaks in the direction of travel for a transverse wave is its A. frequency. • period. • wavelength. • amplitude.

  19. Transverse Waves CHECK YOUR ANSWER The distance between adjacent peaks in the direction of travel for a transverse wave is its A. frequency. • period. • wavelength. • amplitude. Explanation: The wavelength of a transverse wave is also the distance between adjacent troughs, or between any adjacent identical parts of the waveform.

  20. Transverse Waves CHECK YOUR NEIGHBOR The vibrations along a transverse wave move in a direction A. along the wave. • perpendicular to the wave. • Both A and B. • Neither A nor B.

  21. Transverse Waves CHECK YOUR ANSWER The vibrations along a transverse wave move in a direction A. along the wave. • perpendicular to the wave. • Both A and B. • Neither A nor B. Comment: The vibrations in a longitudinal wave, in contrast, are along (or parallel to) the direction of wave travel.

  22. The Nature of Sound

  23. What is Sound? • In human experience: • That • which • we • hear. • In Physics: • Oscillation • of pressure transmitted • through a medium • at frequencies • between • 20Hz and 20 kHz.

  24. Soundtravels in longitudinalwaves — vibrating compressions and rarefactions through air

  25. How do we Hear Sound?

  26. Perceived • Pitch • is proportional to • the freQuency • of the pressure wave. 550 Hz 880 Hz

  27. Perceived • Loudness • is proportional to • the amplitude • of the pressure wave.

  28. How a Loudspeaker Works A radio loudspeaker is a paper cone that vibrates Air molecules next to the loudspeaker are set into vibration This produces compressions and rarefactions in the air

  29. For this Experiment, you will need:water, cornstarch, plastic sheet, speaker, LOUD music

  30. The Speed of Sound In air( ≈340 m/s ) in water( ≈four times speed in air ) in steeL( ≈15 times speed in air ) • air • Water • steeL • For each increase of 1°C above 0°C, • speed of sound increases by 0.6 m/s.

  31. Reverberations-multiple reflections Reflection: process in which sound encountering a surface bounces back and is returned.

  32. Types of Reflection

  33. Refraction: the bending of a wave due to a change in the medium and/or speed of the wave. What affects the speed of a sound wave?

  34. Sound waves refract when air near the ground is warmer than air above.

  35. Dolphins and bats emit ultrasonic waves to enable them to locate objects in their environment.

  36. Humans do the same thing with SONAR*! *SOund Navigation And Ranging

  37. end

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