Acoustics is a branch of physics that deals with the production, transmission, reception, control and effects of sound. This chapter covers sound waves, the velocity of sound, the reflection of sound, echo and the Doppler effect.
1. Sound Waves – Production and Propagation
- Touching a ringing bell or a musical instrument shows that sound is produced by vibrations.
- Vibrating bodies produce energy in the form of waves, which are sound waves.
- Sound needs a material medium like air, water or steel for its propagation. It can travel through a gaseous, a liquid or a solid medium.
- The Moon does not have air, so on the Moon you will not be able to hear any sound produced by your friend.
Longitudinal Waves
- Sound waves are longitudinal waves that can travel through solids, liquids and gases with a speed that depends on the properties of the medium.
- The particles of the medium vibrate along the direction of propagation of the wave, moving from their mean positions.
- This produces a series of high and low pressure regions called compressions (high pressure) and rarefactions (low pressure).