What it shows
Sound travels through the air as vibrations. A loud sound near a stretched plastic sheet makes the sheet vibrate, and grains of rice on it jump, even though nothing touches the drum.
The science
When you bang the plate, it vibrates and pushes the air back and forth, making a sound wave that spreads out in all directions. When the wave reaches the stretched film it pushes the film back and forth too. The film moves only a tiny amount, but enough to toss the light rice grains into the air. Loud sounds push harder, so the rice 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 large steel bowl or a wide-mouthed plastic container
- A piece of cling film or a cut-open plastic bag
- A rubber band to hold the film tight
- A spoonful of uncooked rice or sugar
- A steel plate and a spoon to make a loud sound, or a speaker playing music
Safety
This project uses safe, everyday materials. Still, read the rules below with a parent before you start.
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.
Stretch the cling film tightly over the mouth of the bowl and hold it with the rubber band, smoothing out any wrinkles.
Sprinkle a thin layer of rice grains on the film.
Hold the steel plate about 20 cm away and bang it hard with the spoon; watch the rice jump.
Bang it softly and notice the rice barely moves.
Move the plate further away and find how far you can go before the rice stops dancing.
Hum loudly with your mouth close to the drum and see whether your voice can move the rice.
Place a phone speaker next to the drum, play a low note and then a high note, and compare the movement.
Record your observations: which sounds, how loud and how far away made the rice jump.
What you should see
The rice grains jump every time a loud sound is made nearby, without anything touching the drum. Louder and closer sounds make them jump more, showing that sound carries energy through the air.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Nothing touched the drum, so why did the rice move?
The sound travelled through the air as vibrations and shook the stretched film.
2What happens with a softer sound?
The film vibrates less, so the rice barely moves.
3Can sound travel through empty space?
No, sound needs a material like air, water or a solid to travel through.
4How does your ear hear sound?
The eardrum is a thin skin that vibrates just like the film on the drum.
Take it further
Put the drum in a sealed box with a thick blanket round it and test whether sound still gets through.
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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