What it shows
Rolling is easier than sliding. Rollers under a load reduce the friction, which is how the wheel was a great invention.
The science
When one surface drags over another, friction pulls against the motion. With rollers, the box does not slide on the floor. Rolling friction is much smaller, so the box moves with less effort. This is why trolleys, carts and cars have wheels.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A shoebox filled with books or rice packets
- Six round pencils or ruler-length sticks
- A rubber band
- A cloth bag as a pull bag
- A smooth floor or table
- A tape measure
Safety
For this project: Keep the box light enough for a child. Keep fingers clear of the roller and the box. An adult must watch.
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.
Fill the shoebox with books and tie the rubber band to the front.
Pull the box along the floor by the rubber band and see how far the band stretches.
Make a mark on a paper strip where the band stretched to.
Lay the pencils flat on the floor in a row, side by side.
Place the box on the pencils and pull it with the rubber band again.
Mark the stretch of the rubber band on the paper strip.
Compare the two marks and notice which stretch is smaller.
Keep moving the pencils from the back to the front as the box rolls forward.
What you should see
The rubber band stretches less when the box is on rollers, showing that rolling needs less force than sliding.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why is rolling easier than sliding?
There is less friction between the surfaces.
2What is the rubber band doing?
It shows how much force we pull with.
3Name a thing that uses wheels.
A bicycle, a trolley or a cart.
4Why did we need to move the pencils from the back?
To keep rollers under the front of the box.
Take it further
Use round bottle caps or marbles instead of pencils and compare.
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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