Sound

• 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.