What it shows
A top stays upright while it spins fast, then wobbles and falls as friction slows it. Tops with a wide, heavy rim and a sharp point usually spin for longer.
The science
A spinning object keeps spinning in the same direction until a force slows it, a property called rotational inertia. The more mass is far from the centre, the harder it is to slow, so a wide rim helps the top spin longer. Friction at the tip and with the air slowly takes away its energy. When it slows down enough, gravity makes it tilt and it falls over.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Old CDs, cardboard discs or bottle caps
- Short pencils or sharpened sticks, 4 pieces
- Glue or clay
- Coins to add weight
- A stopwatch or phone timer
- A smooth table or tray
- Pen and paper for a results table
Safety
For this project: An adult must sharpen the sticks. Spin tops on a table away from the edge so small parts do not fly into eyes.
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.
Step 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.
Push a pencil through the centre of a cardboard disc and fix it with glue so the disc is firm.
Make three more tops: a small disc, a big disc, and a big disc with four coins stuck near the rim.
Check each top spins straight. If it wobbles, move the stick to the true centre of the disc.
Spin each top between your thumb and finger on the table and start the timer when it is released.
Stop the timer when the top falls over, and write the time in a table.
Spin each top three times and take the middle value, because the spin can vary a little.
Make a bar chart of the time for each top.
Try the same top on a smooth tray and on a rough cloth and see how the surface changes the time.
What you should see
A bar chart showing the big disc with coins near the rim spins longest and the small disc shortest. The top spins less on a rough surface.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01Why does the top fall at last?
Friction slows its spin until gravity can tip it over.
02Why do coins near the rim help?
Weight far from the centre makes it harder to slow the spin.
03Why is a sharp point good?
It touches the table at a very small area, so there is less friction.
04What keeps the top upright while spinning?
Its spin gives it a steadiness that resists tipping over.
Take it further
Compare how long a top spins when the stick is long or short and decide where its centre of mass should be.
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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