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Mechanical Waves

Mechanical Waves . Ch 17.1. Mechanical Waves. Carries energy from one place to another due to a disturbance in matter Must have a medium Solid Liquid Gas through which the wave travels. Transverse Waves.

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Mechanical Waves

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  1. Mechanical Waves Ch 17.1

  2. Mechanical Waves • Carries energy from one place to another due to a disturbance in matter • Must have a medium • Solid • Liquid • Gas through which the wave travels

  3. Transverse Waves • Causes the medium to vibrate at right angles to the direction in which the wave travels • Parts- • Crest- highest point • Trough- lowest point

  4. Longitudinal Waves • Vibration of the medium is parallel to the direction the wave travels • Parts- • Compression- particles are close together • Rarefaction- particles are spread apart

  5. Surface Waves • Travels along a surface separating 2 mediums

  6. Properties of Mechanical waves Ch 17.2

  7. Period • Time required for 1 cycle – a complete motion that returns a wave to its starting place • Periodic Motion • Regular time intervals

  8. Frequency • The # of complete cycles in a given time • Measured in hertz • Hz, cycles per second

  9. Wavelength • Distance between a point on the wave and the same point on the next cycle of wave • Transverse wave • Adjacent troughs or crests • Longitudinal wave • Adjacent compressions or rarefactions

  10. Wave Speed • SI Units • V= • f = Hz • λ= m • Can change if the wave hits a new medium • If waves travel at constant speed, then wave length is inversely proportional to frequency

  11. Practice • One end of a rope is vibrated to produce a wave with a wavelength of 0.25m. The frequency of the wave is 3hHz. What is the speed? • Given: • Equation: • Solve:

  12. Amplitude • Maximum displacement of the medium from its rest position • The more energy= greater amplitude • Transverse • Distance from rest position to a crest or trough • Longitudinal • Maximum displacement of a point from its rest position

  13. Behavior of Waves Ch 17.3

  14. Reflection • A wave bounces off a surface that it cannot pass through • It does not change the speed or frequency of the wave but the wave can be flipped or turned upside down.

  15. Refraction • The bending of a wave as it enters a new medium at an angle • Happens due to one side of the wave moving slower than the other side

  16. Diffraction • The bending of a wave as it moves around an obstacle or passes through a narrow opening

  17. Interference Constructive Interference Destructive Interference • 2 or more waves combine to produce a wave with larger displacement • 2 or more waves combine to produce a wave with smaller displacement

  18. Standing Waves • Appears to stay in one place • As if not moving through a medium • Parts- • Node- point with no displacement from the rest position • Antinode- point where a crest or trough occurs midway between 2 nodes • Forms only if half a wavelength or multiple of half a wavelength fits exactly into the length of a vibrating cord

  19. Sound and Hearing Ch 17.4

  20. Properties of Sound Waves • Longitudinal waves • Compressions and rarefactions that travel through a medium • Speed • Intensity • Loudness • Frequency • Pitch

  21. Properties of Sound Waves Speed • In dry air @ 20 °C • Speed of sound= 342m/s • Speed varies in mediums • Solids fastest • Liquids • Gas slowest

  22. Properties of Sound Waves Intensity & Loudness • Intensity-rate which waves energy flows through a given area • Depends on waves amplitude and distance from the sound source • Measured in • Decibels, dB • Loudness-physical response to intensity • High frequency=louder

  23. Properties of Sound Waves Frequency & Pitch • Frequency depends on • How fast the source of the sound is vibrating • Pitch is the frequency of a sound as you perceive it • High frequency=high pitch

  24. Ultrasound • Normal sound • 20Hz – 20,000Hz • Infrasound • Frequencies lower than you can hear • Ultrasound • Frequencies higher than you can hear • Used for sonar and imaging

  25. Ultrasound Sonar Ultrasound Imaging • Technique for determining distance to an object under water • Sound Navigation and Ranging • Important in medical field • Maps heart, and babies without interfering with pulse

  26. Doppler Effect • Change in sound frequency caused by motion of • Sound source • Listener • Or both • Closer to sound • Higher frequency • Farther to sound • Lower frequency

  27. Hearing & The Ear • Outer Ear • Middle Ear • Inner Ear

  28. Reproduced Sound • Sound is recorded by converting sound waves into electronic signals that can be processed and stored. • Sound is then reproduced by converting electronic signals back into sound waves

  29. Music • Instruments vary pitch by changing the frequency of standing waves • Resonance amplifies sound • The response of a standing wave to another wave of the same frequency

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