Put your fingers gently on your throat and hum. You can feel a buzz. That buzz is a vibration, and it makes sound.
Key idea
Sound is made when something vibrates (moves back and forth quickly). The vibration passes through the air (or water, or a solid) to your ears. Fast vibrations make a high pitch; slow ones make a low pitch. Bigger vibrations are louder.
| Change | What you hear |
|---|---|
| Shorter or tighter string, smaller drum | higher pitch |
| Longer or looser string, bigger drum | lower pitch |
| Pluck or hit harder | louder |
| Pluck or hit gently | softer |
Sound needs something to travel through. In space there is no air, so there is no sound: astronauts talk by radio. Sound travels faster through water and solids than through air. Put your ear on a table while someone taps the far end!
Worked example: Which is higher?
A big tuba and a small flute play. Which usually plays higher notes?
- Small instruments have short tubes and fast vibrations.
Answer: The flute.
Common mistake
Mixing up loud and high. A lion's roar is loud and low; a mouse squeak is soft and high.
Try it at home
- Stretch rubber bands of different thickness around an open box or a plastic tub.
- Pluck each. Which sounds higher: thin or thick? Tight or loose?
- Fill glasses with different amounts of water and tap them gently with a spoon. Which is highest?
Going further. Learn to read the notes in Music; see waves in Pendulums and Resonance; and later Sound in Physical Science.