Ch 17 Mechanical Waves Sound Section 17 1

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) – Created when a source of energy causes a vibration to travel through a medium – 3 main types of mechanical waves: 1. Transverse 2. Longitudinal 3. Surface

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

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

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)

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-tocrest) –Frequency – the number of complete cycles in a given time • Measured in cycles per second [hertz (Hz) = 1/sec]

• 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)

• 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)

• 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)