Sounds are caused by vibrating sources. Vibrating sources cause the air around them to vibrate, which are passed to our ears where they cause the eardrum to vibrate and we hear sound.
A medium is needed to transmit sound waves. Sound travels faster in solids than in liquids and faster in liquids than in gases. The molecules are closer together, and pass on energy quicker.
Sound waves are longitudinal.
Approximate range of frequencies audible to humans as 20 Hz to 20 000 Hz.
- Ultrasound – Sound with a frequency higher than 20 kHz.
Speed of sound in the air is approximately 330–350 m/s.
Speed of sound in air = distance ÷ time
- Echo – The reflection of sound waves.
| Compressions | Rarefactions |
|---|---|
| Air molecules are compressed together. | Air molecules spread out. |
| High air pressure. | Low air pressure. |