Mechanical Waves and Sound
How a disturbance travels through matter - and why we can hear it
Big Idea: A mechanical wave is a disturbance that travels through a material (a medium) and carries energy from one place to another without carrying the matter along with it. The particles of the medium only oscillate about their fixed positions; it is the pattern of the oscillation that moves. Sound is exactly such a wave, and echo, ultrasound and infrasound are all sound obeying the same rules.
By the end of this topic you will be able to:
- distinguish transverse and longitudinal waves,
- use the wave quantities wavelength, frequency, period and speed, and the relation v = λf,
- describe sound as a longitudinal wave and name what sets its pitch and loudness,
- explain echo and resonance, and
- compare infrasound, audible sound and ultrasound and their uses.