Sound & vibration
The idea
Every sound starts with a vibration — something moving back and forth very fast. A drum skin jumps up and down, a guitar string blurs from side to side, and your throat buzzes when you hum. The vibration shakes the air around it, and that shaking travels through the air to your ears. Rest your fingers gently on your throat and hum: the tiny buzz you feel is the start of every word you say.
Two simple rules connect vibration to sound. Bigger vibrations make louder sounds, and no vibration means no sound at all — stop the shaking and the sound dies instantly. A common mix-up is thinking sound leaks out of objects the way smell drifts out of a kitchen. Sound is not stored inside things; it is made fresh each time something vibrates, and the moment the moving stops, there is nothing left to hear.
Worked example
You stretch a rubber band over an open shoebox. You pluck it gently, then pluck it hard, then pluck it once more and quickly pinch the band still with two fingers. What do you see, hear, and feel each time?
- Pluck the band gently and look closely: it turns into a soft blur as it wobbles back and forth fast, and you hear a quiet twang. The blur is the vibration making the sound.
- Pluck it hard: the blur is wider, because the band swings farther on each wobble, and the twang is clearly louder. A bigger vibration makes a bigger sound.
- Pluck it again and immediately pinch the band still: the sound cuts off the instant the band stops moving. No vibration, no sound.
- Touch the box while a twang is still ringing: you can feel a faint buzz in the cardboard, which shows the vibration spreading from the band into the box and the air.
- Put the clues together: every sound matched a vibration you could see or feel, and the sound was loud exactly when the vibration was big.
Answer. The sound comes from the band's vibration: harder plucks make wider wobbles and louder twangs, and pinching the band still silences it at once.
Check your understanding
- What is vibrating when you clap your hands, and how could you test your idea?
- Why does resting your fingers on a ringing bell or a humming guitar string make the sound stop?
- How could you make the rubber band play a quieter twang or a louder twang on purpose, without swapping the band?
- Where can you feel a sound with your body instead of hearing it, and what does that tell you about what sound is?