A vibrating object sends sound waves through the air because its surface pushes and pulls repeatedly on the air. When the waves reach your ears, they make your eardrums vibrate in and out so you can hear sound as a result.
- Sound waves cannot travel through a vacuum.
- Sound waves are longitudinal waves. The waves vibrate along the direction they travel in. Electromagnetic waves (e.g. light) are transverse waves. They vibrate at right angles to the direction they travel in.
The reflection of Sound:
A sound echo is an example of reflection of sound. Echoes can be heard in a large hall or gallery which has bare, smooth walls.
- If the walls are covered in soft fabric, the fabric will absorb sound instead of reflecting it, and so no echoes will be heard.
- If the wall surface is uneven, not smooth, echoes will not be heard because the reflected sound is 'broken up'
The refraction of Sound:
At night you can hear sound a long way from the source of the sound. This is because it refracts back to the ground instead of travelling away from the ground. Refraction takes place at the boundaries between layers of air at different temperatures. In the daytime, sound refracts upwards not downwards because the air near the ground is warmer than higher up.