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Mechanical Waves

Mechanical Waves. Pendulum. Swinging mass in harmonic motion due to gravity. Time and number of swings are most useful data you will collect. Period ( T ). Time required to make one complete swing. seconds. Frequency (f). The number of swings in a certain time.

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Mechanical Waves

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  1. Mechanical Waves

  2. Pendulum Swinging mass in harmonic motion due to gravity. Time and number of swings are most useful data you will collect

  3. Period (T) Time required to make one complete swing.seconds Frequency (f) The number of swings in a certain time. swings per second = 1/s = Hertz (Hz)

  4. T and f are related or

  5. Period Frequency

  6. Examples of Frequency • What is the frequency of the second hand of a clock? Frequency = 1cycle/60 s Period = 60 s What is the frequency of US Presidential elections? Frequency = 1 election/4 yrs Period = 4 yrs

  7. WAVE MOTION • Energy is transferred by particles or waves. • A mechanical wave is a disturbance transmitted through a medium (matter). • Two types of mechanical waves: transverse and longitudinal

  8. Particles vibrate perpendicular to the propagation of the wave The propagation of a wave is determined by the direction the energy is transferred TRANSVERSE WAVES

  9. Crest l Wavelength A A - Amplitude Trough Picture of a Transverse Wave Rest position

  10. WAVE SPEED The average speed is defined as

  11. For a wave, if the distance traveled is a wavelength (l), then the time to travel this distance is the period (T). Thus or

  12. is true for all waves. Note: v is dictated by the medium. f is dictated by the source. l is dependent on the n and f

  13. LONGITUDINAL WAVES Particles vibrate arallel to the propagation of the wave Rest Position | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Wave |||| | | | | | | | | | | | | | | | | |||| | | | | | | | | | | rarefaction compression wavelength

  14. Compressions are regions of high density. Rarefactions are regions of low density. Wavelengthis the distance between….. ………….successive rarefactions or ………….successive compressions.

  15. Natural Frequency All materials have a natural frequency of vibration • The longer an object the lower the natural frequency - pendulum • The thicker the material the lower the natural frequency – guitar strings • Less tension makes it “thicker” • More tension makes it “thinner”

  16. Wave interference A number of different waves can be in the same place at the same time, the resulting combination is described as interference. Destructive interference results in a loss of amplitude Constructive interference results in a gain of amplitude

  17. Complete constructive interference occurs when waves are in sync, that is when the crests line up and the troughs line up.

  18. Complete destructive interference occurs when waves are half a wave out of sync, that is when crests overlap with troughs.

  19. Standing Waves • 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.” • When a wave is reflected off a fixed boundary it “flips over”. As the reflected wave passes by the

  20. There is maximum vibration at an antinode. l is twice the distance between successive nodes or successive antinodes. l There is no vibration at a node.

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