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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 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 - When entering a new medium When pressure and temperature change
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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