When a musician plays, sounds spread outwards from their instrument. Anyone nearby can hear the sounds. This shows that sound can travel through air.
Sound can also travel through solids and liquids. For example, place your car against a table. Ask someone to tap the table - you will hear the tapping sound very clearly.

Sound and a vacuum

The picture shows an experiment to find out whether sound can travel through a vacuum (an empty space, with no air in it). An electric bell is hanging in a glass bell-jar. At first, the girl can hear it ringing.
Then the air is pumped out of the jar, so there is a vacuum in the jar. Now the girl cannot hear the bell. She can see that it is still ringing.
Sound needs a material to travel through. The material can be solid, liquid or gas. Sound cannot travel through a vacuum.

Sound travelling

You should remember that air is made up of tiny particles called molecules. By thinking about these particles, we can explain how sound travels.

When a loudspeaker makes a sound, its cone vibrates back and forth. This pushes the air molecules next to the cone so that they move back and forth with the same frequency. These molecules then push on the next layer of molecules so that they also start to vibrate.
These molecules push on the next ones, and so on. The molecules only vibrate from side to side, but the vibration travels outwards through the air. We call this a sound wave.
Take care! Molecules of the air do not travel all the way from the loudspeaker to your ear. You hear the sound because the vibrations are passed along from one molecule to the next.