How sound travels
Physics · Key Stage 2 · The School
Every sound starts with a vibration
Rest your fingers on your throat and hum: that buzzing is your vocal folds vibrating. Ping a ruler over the edge of a desk and you can SEE the vibration that makes the sound. Stop the vibration — grab the ruler — and the sound stops instantly. There is no exception to this: no vibration, no sound.
It needs something to travel through
The vibration pushes the particles next to it, which push the ones next to them, and that pattern travels outward to your eardrum, which vibrates in turn. Sound can travel through air, water and solids — put your ear to a desk and tap it, and it is louder, because the particles in a solid are packed close and pass the push on faster. Where there are no particles at all, in space, sound cannot travel.
Pitch and volume are different things
PITCH is how high or low a sound is, and it depends on the object: shorter, tighter, thinner things vibrate faster and sound higher. Line up bottles with different water levels and tap them to hear it. VOLUME depends on how much energy you put in — a harder hit makes a bigger vibration and a louder sound. And every sound gets fainter with distance, because the vibration spreads out as it travels.
Have a friend tap the far end of a long wooden table while you listen from the other end. Now put your ear flat against the table and have them tap exactly the same way. It is markedly louder and sharper through the wood. The vibration passes from particle to particle, and in a solid the particles are packed close and strongly linked, so the wave carries better and faster than through the loose particles of air.