Physics Sound

• Sound


  A form of energy. Sounds are made when things vibrate. The vibrations are passed on by particles in solids, liquids or gases. Sound needs a substance to pass on the vibrations, so it can travel through solids, liquids and gases but not through a vacuum. Sound travels as a longitudinal wave. The vibrations are parallel to the direction of the wave.
• Wavelength


  The distance between two compressions
• Speed of sound


  Faster through solids than liquids, and slowest through gases. This is because the particles are very close together in solids and so the energy is more likely to be passed from one particle to the next.
• Frequency


  The number of vibrations each second. The unit is hertz (Hz).
• Pitch


  High pitched sounds have a high frequency, and low pitched sounds have a low frequency.
• Time period


  The time for 1 wave to pass. It can be measured between any point on a wave and the same point of the next wave.
• Amplitude


  Half the height of the wave. The loudness of a sound depends on the amplitude.
• Louder notes have more energy and the wave has a bigger amplitude.
• Sound wave characteristics


  • High frequency, high pitch
  • Low frequency, Low pitch
  • Medium frequency, medium pitch
  • High amplitude- Very loud
  • Low amplitude- Low volume
  • Medium amplitude
• Measuring speed of sound

  1. Use a large distance (preferably over 50 metres)

  2. Use an electronic timer or data logger to record the time taken
• Methods to measure speed of sound

  • Clap-echo method
  • Data logger measuring time between two microphones
• Ultrasound


  Sound waves with a frequency greater than the human hearing threshold (above 20 000Hz). Used for navigation by dolphins and bats, and for pre-natal scanning.
• Infrasound


  Anything with a frequency below 20 Hz, which cannot be heard by the human ear.
• Ear


  • Sound waves travel through the air and into the ear, causing the eardrum to vibrate. The vibrations are passed through three small bones (ossicles) to the cochlea, which converts the vibrations into electrical signals that are passed to the brain through the auditory nerve.
• Hearing range


  The range of pitches that a person or animal can hear. Humans can hear from 20Hz to 20,000Hz (20kHz).
• Decibel (dB)


  A unit used to measure the loudness of a sound.
• Soft materials can absorb sound and are used in soundproofing and for making ear protectors.
• Loud sounds


  Can damage the eardrum or the cochlea, particularly the sense cells in the cochlea.
• People who work in very noisy places must wear ear protection.
• Noise


  Unpleasant sound.