Sound

• Features of sound we can describe

  • Pitch
  • Volume
• Pitch


  High or low
• Volume


  Loud or quiet
• Frequency


  Number of vibrations per second, measured in hertz (Hz)
• Higher frequency


  Higher pitch
• Factors that increase pitch

  • Increase the tension
  • Decrease the length
  • Decrease the diameter / thinner string
• Mass


  Higher mass causes fewer vibrations per second, resulting in lower pitch
• Sound is caused by vibrations
• Sounds

  • Aircraft taking off (loud)
  • Whistle (high)
• Sound travels in the air because particles pass on vibrations
• Pitch


  How high or low a sound is
• Volume


  How loud or quiet a sound is
• Low pitch sounds


  Caused by slow vibrations
• Frequency is measured in Hertz
• Sound production by a tuning fork

  1. Prongs vibrate (move forwards and backwards)

  2. Forward movement pushes air particles together, creating compression (high pressure)

  3. Backward movement pulls air particles apart, creating rarefaction (low pressure)

  4. Pushing and pulling of air particles creates a sound wave that transfers energy through the air
• Sound waves


  • Longitudinal waves, vibrations are parallel to direction of energy transfer
• Light


  • Transverse wave, vibrations are perpendicular to direction of energy transfer
• Wavelength


  Distance from a point on one wave to the equivalent point on the next wave
• Amplitude


  Maximum displacement of a point on a wave away from its undisturbed position
• Analysing sound


  1. Record using microphone

  2. Display on oscilloscope

  3. Oscilloscope image shows transverse wave with same frequency and amplitude as longitudinal sound wave
• Volume


  Linked to amplitude, larger amplitude means louder sound
• Wavelength


  Linked to pitch, shorter wavelength means higher frequency and higher pitch
• Sound requires particles to travel, cannot travel through a vacuum
• Sound wave is reflected


  Energy transfers back to the room as a sound wave, creating an echo
• Sound wave is absorbed


  Energy transfers to the object, no energy transfers back to the room, this is how soundproofing works
• Speed of sound


  • Fastest through solids
  • Followed by liquids
  • Then gases
• This occurs because in a mechanical wave, energy is transmitted through particles physically coming in contact with each other