What it shows
A twisted rubber band stores elastic energy that turns the axle and moves the car. Winding it more stores more energy and the car goes farther.
The science
Twisting or stretching the rubber band stores elastic potential energy. When released, it turns the rear axle, and friction between the wheel and the floor pushes the car forward. More turns store more energy, so the car goes farther. The wheels, axles and straws must be smooth to reduce friction, or the energy is wasted as heat.
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.
- Four old CDs or bottle caps for wheels
- Two bamboo skewers for axles
- A cardboard chassis 20 cm by 8 cm
- Two straws to hold the axles
- A strong rubber band
- Tape and a hook of wire
- A tape measure
Safety
For this project: An adult must cut the skewers and cardboard. Keep fingers away from the stretched band.
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.
Glue two straws across the chassis as axle holders.
Push a skewer through each straw and fix wheels at the ends.
Attach a hook of wire or a toothpick to the rear axle.
Tie the rubber band to the front of the chassis.
Hook the other end on the rear axle hook and wind the wheels backward to stretch the band.
Place the car on the floor and release.
Measure the distance for 10, 20 and 30 winding turns.
Plot distance against turns on a graph.
What you should see
The car moves a few metres and the distance rises with the number of winds, up to a limit.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What type of energy is stored in the band?
Elastic potential energy.
2Why does more winding give more distance?
More energy is stored.
3What wastes energy in the car?
Friction.
4How can you reduce friction?
Use smooth straws and a little oil on axles.
Take it further
Change wheel size and see which gives a longer run.
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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