Vibration in the tuning fork produces disturbances in the surrounding air. When the prongs’ movement is outwards, the prongs push the surrounding air molecules away, creating a local compression.
This disturbance of air layers is then passed from molecule to molecule by collisions, causing the local compression to move outwardly.
When the prongs’ movement is inwards, a partial void, or rarefaction is created. Pressure differences causes the air molecules to rush back into the region again. This periodic to-and-fro movement of the prongs will create alternating regions of compressions and rarefactions. The sound waves span outwardly parallel to the direction of the wave propagation (longitudinal nature).
- In air, compressions are regions where the pressure is higher than surrounding air and rarefactions are regions where pressure is lower than the surrounding air.
- The energy of the sound waves is propagated and carried by colliding particles of a material medium. Hence, a (material) medium is required in order to transmit these (energy) waves.
- The speed of energy propagation is dependent on the proximity of these particles in a medium. Hence, given that the proximity of particles in the air, liquids or solids is different, the speed of sound differs in air, liquids and solids. Sound travels faster in denser media. It travels faster in liquids than in gases and fastest in solids.