What it shows
Water can turn a wheel by weight from above (overshot) or by push from below (undershot). Timing how fast each wheel lifts a small weight shows which uses water more efficiently.
The science
In an overshot wheel, water falls into cups at the top, and its weight turns the wheel down. In an undershot wheel, moving water pushes paddles at the bottom. The overshot wheel uses the potential energy of falling water as well as its flow, so it usually lifts more with the same water.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Two plastic or card discs 12 cm wide with 8 spoon-shaped cups each
- Two skewers for axles
- A bottle with a tap hole to supply water
- Thread and a paper clip as the load
- A tray to catch water
- A stopwatch and a measuring cup
Safety
For this project: Work over a tray or outdoors to avoid slipping. An adult must cut plastic and skewers. Keep electrical items away from the water.
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.
Make an overshot wheel by gluing eight cup-shaped scoops around the rim of a disc.
Make an undershot wheel by gluing eight flat paddles pointing outwards around another disc.
Mount each wheel on a skewer held up by two stands made of card or cups.
Tie a thread to the axle so that it winds up a paper clip load as the wheel turns.
Pour 500 ml of water from a fixed height into the overshot wheel at a steady pace and time the lift of the load.
Repeat with the undershot wheel by letting the water run under the paddles from a small ramp.
Do three trials for each wheel and average the times.
Compare height lifted per cup of water in each case.
What you should see
The overshot wheel lifts the load higher or faster using the same volume of water than the undershot wheel. Averaged times make the difference clear.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Which wheel uses the weight of water?
The overshot wheel.
2What energy change occurs?
Gravitational potential energy to kinetic energy and then to lifting work.
3Why average three trials?
It reduces random errors.
4Where were water wheels used?
In old flour mills and for lifting water on farms.
Take it further
Vary the number of cups to find which count gives the quickest lift.
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
Science projects
Physics Working Models Explained
Twenty classic models, how each works and how to make it