What it shows
A cardboard bird with coins hidden in its wing tips balances on its beak and even wobbles back upright when pushed. Adding weight far forward and low moves the bird’s centre of gravity to just below the beak, so it cannot topple.
The science
Every object has a point called its centre of gravity where all its weight seems to act. An object balances when its centre of gravity is directly below or above the support, and it is stable, returning after a nudge, when the centre of gravity is below the support point. The bird’s wings sweep forward with coins in the tips, so most of the weight sits ahead of and below the beak. When the bird tips, its centre of gravity rises a little, and gravity pulls it straight back down to the balanced position, which makes it rock instead of fall.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Stiff cardboard from a carton (free)
- Two one-rupee coins or two washers
- Scissors, pencil and glue or tape
- Colours to decorate
- A pencil or your finger as the balancing point
Safety
For this project: Children should use safety scissors on cardboard; an adult can cut thicker card.
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.
Draw a bird on the cardboard with a sharp beak at the front and two wide wings sweeping forward so the wing tips reach further forward than the beak.
Cut the bird out and colour it.
Try balancing it on your fingertip by the beak; it falls because the weight is behind the beak.
Tape one coin under each wing tip, in exactly the same place on both sides.
Balance the beak on your fingertip again; it should now hang level and steady.
Give the tail a gentle push and watch it rock and settle back.
Move the coins slightly backwards and find the point where the bird no longer balances.
Perch it on the tip of a pencil standing in a lump of clay and display it as a desk ornament.
What you should see
The bird balances on its beak on a fingertip or pencil point, swaying back upright after each push. Without the coins, or with the coins too far back, it falls off.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is the centre of gravity?
The point where the whole weight of an object seems to act.
2Why does the bird balance only with the coins?
The coins move the centre of gravity forward and below the beak, directly under the support.
3Why does it swing back when pushed?
Tipping lifts its centre of gravity, and gravity pulls it back down to the lowest position.
4Why is a bus with a heavy roof load easier to tip?
A high load raises the centre of gravity, so it tips over more easily.
Take it further
Make a balancing clown from a cork and two forks, or a balancing butterfly from a sweet wrapper and two coins.
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.
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