What it shows
Turning a large wheel moves a small axle with greater force, so a bucket of water can be lifted with a light push on the handle. The bigger the handle circle compared with the axle, the easier the lift but the more turns needed.
The science
A wheel and axle is a lever that goes round and round. Your hand on the rim of the big wheel moves through a large circle while the string winds on the thin axle through a small circle. Because you move further, you need less force, in the same ratio as the two radii: a handle five times wider than the axle lets you lift the bucket with about one fifth of the force, but you must turn five times as far. Village wells, door knobs, steering wheels and screwdrivers all work this way.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A cut-down plastic bottle or a paper cup as the well (free)
- A pencil as the axle and a large bottle cap or a cardboard circle as the wheel or handle
- Two ice cream sticks or a cardboard frame to hold the axle
- String and a small bottle cap as the bucket
- A little water and a tray
- Glue and tape
Safety
For this project: An adult must make the holes in the frame; do the water part on a tray.
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.
Stand two ice cream sticks upright on either side of the well cup and glue them firmly to a cardboard base.
Make a hole near the top of each stick, push the pencil through both, and check it turns freely.
Glue the large bottle cap or cardboard circle to one end of the pencil as the wheel, with a small stick glued on its rim as a handle.
Tie the string to the middle of the pencil and tie the small bottle cap bucket to the other end.
Fill the well with a little water, lower the bucket by unwinding, and turn the handle to lift it up full.
Now try turning the bare pencil end with your fingers instead of the handle, and feel how much harder it is.
Swap the wheel for a bigger cardboard circle and count how many turns it takes to raise the bucket, then compare with the small one.
Decorate the well with a cardboard roof and write a label explaining the wheel and axle.
What you should see
The bucket rises full of water with an easy turn of the handle. Turning the bare axle is much harder, and a larger wheel makes it easier still but needs more turns.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Which part is the wheel and which is the axle?
The bottle cap with the handle is the wheel and the pencil is the axle.
2Why is the handle easier than turning the pencil directly?
Your hand moves through a bigger circle, so less force is needed for the same lift.
3What is the cost of using a bigger wheel?
You have to turn it further, so more turns are needed.
4Name two wheel-and-axle machines at home.
A door knob and a tap handle, or a screwdriver and a steering wheel.
Take it further
Add a ratchet made from a cardboard toothed wheel and a stick pawl so the bucket does not drop back when you let go.
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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