General properties of waves - sound

sound is a longitudinal wave travelling in a medium, created by a vibrating source
- medium particles are not transported away from the source
- direction of vibration is parallel to the direction of wave travel

the forward and backward vibration of a source is passed on to the air particles
causes alternate regions of the air particles to be compressed and extended
- compressed regions are called compressions
- extended regions are called rarefactions

pitch is related to frequency of the sound wave
- higher the frequency, higher the pitch
loudness is related to amplitude of the sound wave
- larger the amplitude, louder the sound

echo is the repetition of a sound due to the reflection of the sound
formed when a sound is reflected off a hard, flat surface (large wall)
echoes obey the laws of reflection
- the angle of incidence is equal to the angle of reflection

human being cannot hear low frequency sounds (infrasound) and high frequency sounds (ultrasound)
- ultrasound is sound with frequencies above the upper limit of the human range of audibility
sonar (sound navigation and ranging)
- ultrasonic pulse is emitted into the water and the reflected pulse is obtained
  - strength of the reflected pulse depends on the distance and characteristics of the reflecting objects
  - can be used to
    - detect location
    - measures depths
  - $v=\frac{2d}{t}$
pre-natal scanning
- pulses of ultrasound are sent to the womb of a pregnant woman via a transmitter
- images of foetal development are obtained via the reflected ultrasound
  - strength, direction and timing of each reflected pulse is measured to allow the reflecting surface within the womb to be mapped