# Sound

Source: https://projectgcse.co.uk/physics/waves/sound

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- Sound waves are caused by vibrations in the air. They cannot travel through vacuums. The denser the material, the faster sound can travel.
- Sound waves are reflected and this is heard by us as an echo. The echo is the sound being reflected - just like light reflected from a mirror.
- Ultrasound has a very high frequency and we can not hear it but bats use it to fly and it is also used to look inside the body.