What it shows
Voice is a vibration. We can feel it in the throat and see the vibration make salt grains jump on a stretched sheet.
The science
When you speak, vocal cords in your throat vibrate. These vibrations push the air and travel as sound. A stretched sheet over a bowl moves with the sound and makes salt grains jump. Louder sounds make bigger vibrations, so the salt jumps higher.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A steel bowl
- Cling film or a thin polythene sheet
- A rubber band
- A pinch of salt or sugar
- A tray or steel plate and a spoon
Safety
For this project: An adult must supervise. Do not shout close to anyone’s ear.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Put your fingers on your throat and hum. Feel the buzz.
Stop humming and feel that the buzz stops.
Stretch cling film tightly over the bowl and fix it with a rubber band.
Sprinkle a pinch of salt on top of the film.
Hold a tray near the bowl and hit it with a spoon, or shout “aaa” close to the bowl.
Watch the salt jump and dance.
Try loud and soft sounds and see how the jumping changes.
Write what you see and feel.
What you should see
You feel your throat buzz while humming and the salt jumps on the film when you make a loud sound nearby.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What do you feel in your throat?
A vibration from the vocal cords.
2Why does the salt jump?
Sound vibrations shake the film.
3Does louder sound jump higher?
Yes.
4What carries sound to the film?
The air.
Take it further
Make a low note and a high note and see which makes the salt dance more.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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