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Ch. 17 – Mechanical Waves & Sound

Ch. 17 – Mechanical Waves & Sound. Section 17.1 & 17.2. 17.1 - Mechanical Waves. Mechanical Wave: a disturbance in matter that carries energy from one place to another. Requires matter to travel through (medium) Medium = solids, liquids or gases Outer space = empty (no medium)

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Ch. 17 – Mechanical Waves & Sound

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  1. Ch. 17 – Mechanical Waves & Sound Section 17.1 & 17.2

  2. 17.1 - Mechanical Waves • Mechanical Wave: a disturbance in matter that carries energy from one place to another. • Requires matter to travel through (medium) • Medium = solids, liquids or gases • Outer space = empty (no medium) • Created when a source of energy causes a vibration to travel through a medium • 3 main types of mechanical waves: • Transverse • Longitudinal • Surface

  3. Transverse Waves • Def. – a wave that causes the medium to vibrate at right angles to the direction in which the wave travels. • Crest = highest point on a wave • Trough = lowest point on a wave

  4. Longitudinal Wave • Def.- a wave in which the vibration of the medium is parallel to the direction the wave travels • Compression= an area where the particles in a medium are spaced close together • Rarefaction = an area where the particles in a medium are spread out

  5. Surface Wave • Def. – a wave that travels along a surface separating 2 media • Combination of transverse and longitudinal waves • Example – ocean waves (between water and air)

  6. 17.2 – Properties of Mechanical Waves • Frequency & Period • Periodic motion – any motion that repeats at regular time intervals • Period – the time required for one cycle; a complete motion that returns to its starting point (crest-to-crest) • Frequency – the number of complete cycles in a given time • Measured in cycles per second [hertz (Hz) = 1/sec]

  7. Wavelength (λ – lambda) • Def. = the distance between a point on one wave and the same point on the next cycle of waves • Crest to crest on transverse wave • Compression to compression on longitudinal wave • Increasing the frequency of a wave decreases its wavelength (See below)

  8. Wave Speed (v) • Speed can change: - When entering a new medium • When pressure and temperature change • If wave speed is constant then: • Wavelength is inversely proportional to frequency (as wavelength increases, frequency decreases)

  9. Amplitude • Def. – the maximum displacement of the medium from its rest position • Transverse waves • The distance from the rest position to a crest or a trough • Longitudinal waves • The maximum displacement of a point from its rest position • The more energy a wave has, the greater its amplitude (↑energy = ↑amplitude)

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