Sound travels through different things
Physics · Key Stage 1 · The School
Sound needs something to travel through
Sound cannot travel through nothing at all. It always needs a material to move through. Air is one material. But sound can travel through solids too. And it can travel through water. Air is not the only path. Try each one yourself.
The string telephone test
Make a telephone from two paper cups and a long string. Pull the string tight. Speak quietly into one cup. Your friend hears it clearly in the other cup. The sound travelled along the string, a solid, not just through the air.
Knocking on a table
Put your ear flat against one end of a long table. Ask a friend to knock gently on the other end. You will hear it clearly through the wood. Sit up and listen through the air only. The knock sounds much quieter that way.
Comparing three paths for the same knock
Knock on a table exactly the same way three times. First, listen with your ear flat on the table — you hear it loud and clear through the solid wood. Second, listen with your ear a few centimetres above the table, in the air — quieter. Third, ask a friend to knock while you cover both ears completely — almost nothing gets through at all. Same knock every time. Only the path the sound travelled through changed.
Sound through water
Sound travels through water too, and often very well. Two swimmers underwater can sometimes hear a tap on the side of the pool clearly. Whales use this. Their calls travel huge distances underwater, far further than a shout could ever travel through air.