Unit 3 Properties of waves

Notes

Sound wave characteristics

  • The speed of sound varies from material to material. A sound wave compresses (pushes together) and rarefies (spreads apart) the particles of the material, and how easily this happens affects the speed of the wave.
  • Sound travels fastest in solids because the molecules in a solid are very close together.
  • Sound travels second fastest in liquids because the molecules in a liquid are only slightly further apart.
  • Sound travels slowest in gases because the molecules in a gas are far apart.
  • Remember: Sound cannot travel through a vacuum because there are no particles.
  • Some examples of the speed of sound in different media are given below.
    • In dry air at 0°C the speed is 330m/s.
    • In dry air at 20°C the speed is 340m/s.
    • In water the speed is 1500m/s.
    • In gold the speed is 3200m/s.
    • In steel the speed is 5800m/s.
  • Frequency, pitch, wavelength and amplitude are terms associated with sound waves.
  • Frequency is the number of wavelengths produced per second and its unit is the hertz (Hz).
  • Pitch is how high or low a sound is and is dependent on frequency.
  • Wavelength is the distance from any point on one wave to the same point on the adjacent wave. Its unit is the metre (m).
 
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