What it shows
Two gears with teeth that mesh turn in opposite directions, and a small gear spins faster than a big one.
The science
A gear is a wheel with teeth. When two gears touch, the teeth of one push the teeth of the other, so they turn in opposite directions. If one gear has fewer teeth, it has to turn more times for the bigger one to turn once. So a small gear driven by a big one turns faster.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A flat cardboard sheet (free)
- Two paper cups or bottle caps as templates
- A pencil and scissors
- Two pins or brass paper fasteners
- A thermocol or cardboard base
- A marker
Safety
For this project: An adult must cut the cardboard and press the pins. Keep pins away from small children.
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.
Trace a large circle and a small circle on the cardboard using the cups as guides.
Cut them out and draw 16 teeth around the big circle and 8 around the small one.
Ask an adult to cut out the teeth as small squares.
Pin both gears on the base so their teeth touch each other.
Mark one tooth of the big gear with a marker dot.
Turn the big gear one full turn and count how many times the small gear turns.
Check that the gears turn in opposite directions.
Try a small gear driving the big gear and describe the speed.
What you should see
The small gear turns twice for each turn of the big one and spins in the opposite direction.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is a gear?
A wheel with teeth.
2Which way does the second gear turn?
The opposite way.
3Which turns faster, the big gear or the small gear?
The small gear.
4Where are gears used?
In bicycles, clocks and cars.
Take it further
Add a third gear and say which way it turns.
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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