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)