Sound

Introduction

This topic explores the key concepts of sound as they relate to:

  • the nature of sound
  • the transmission of sound
  • resonance
  • the speed of sound
  • sound and hearing.

Key concepts of sound

The activities in this topic are designed to explore the following key concepts:

  • The production of sound requires an object to vibrate.
  • The speed of the vibration of a sound source gives the frequency of the sound.
  • The size or amplitude of the vibration gives the loudness of the sound.
  • Sounds that reflect off objects are echoes.
  • Sound travels much faster in solid objects than in air.
  • Sound requires a medium to travel in. Sound can't travel in space.
  • The particles in the material in which the sound moves vibrate at the same frequency as the source.
  • Sound is the transmission of kinetic energy from particles in the source to particles in the medium in which the sound travels.
  • Sound travels as a travelling disturbance (wave) due to collisions in the material in which it moves.
  • Sound waves are disturbances called 'longitudinal waves'; the particles in the material vibrate forwards and backwards in the forward-moving wave direction.
  • Sound is pressure waves of compressions (high pressure) and rarefactions (low pressure) travelling away from a vibrating source.
  • Most sounds that are heard are a result of resonance.
  • Objects have their own natural vibration patterns (resonant frequencies) and can give a characteristic note (frequency) when hit (or blown).
  • Resonance is the natural amplification of sound frequencies (resonant frequencies) in an area (resonating chamber) different from the sound source.
  • Speaking and hearing are resonance effects. The mouth and nose cavity acts as a resonating chamber for speech; the ear canal acts as a resonating chamber for hearing.
  • The speed of sound in air is approximately 340 m/s.
  • We use two ears to judge the direction of a sound source.

Students' alternative conceptions of sound

Research into students' ideas about this topic has identified the following non-scientific conceptions:

  • The loudness and pitch (or frequency) of sounds are confused with each other.
  • You can hear and see a distant event at the same moment.
  • Hitting an object harder changes its pitch.
  • In a telephone, actual sounds, rather than electrical impulses, are carried through the wire.
  • Human voice sounds are produced by a large number of vocal cords.
  • Sound moves faster in air than in solids (air is 'thinner' and forms less of a barrier).
  • Sound moves between particles of matter (in empty space) rather than through matter.
  • Sound can travel through space.
  • In wind instruments, the instrument itself, not the internal air column, vibrates.
  • As sound waves move, matter moves along with them.
  • The pitch of whistles or sirens on moving vehicles is changed by the driver as the vehicle passes.
  • The pitch of a tuning fork will change as the tines of the fork slow down (run out of energy).

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