This topic explores the key concepts of sound as they relate to:
- the nature of sound
- the transmission of sound
- 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).