What it shows
A shadow forms because light travels in straight lines and cannot bend round an object. Moving the puppet nearer the torch makes its shadow larger and fuzzier; nearer the screen makes it smaller and sharper.
The science
Light from the torch spreads out in straight lines. Where the puppet blocks those lines, no light reaches the screen and we see a dark shape, the shadow. Because the rays spread out from the torch, a puppet close to the torch blocks more of them and throws a bigger shadow. The butter paper lets the light through so the audience on the other side sees the shadow.
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 or any cardboard box (free)
- White butter paper or tracing paper for the screen
- Cardboard for puppets and drinking straws or sticks for handles
- A torch or a mobile phone light
- Scissors, tape and glue
Safety
For this project: An adult must cut the window in the box; children cut only the puppets with safety scissors.
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
9 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.
Cut a large window in the bottom of the shoebox, leaving a frame of about 2 cm all round.
Tape butter paper tightly over the window from the inside to make the screen.
Draw animal or people shapes on cardboard, cut them out and tape each to a straw as a handle.
Darken the room, stand the box on its side with the screen facing the audience and shine the torch from behind.
Hold a puppet between the torch and the screen and watch its shadow appear on the paper.
Move the puppet slowly towards the torch and see the shadow grow bigger and blurrier.
Move it close to the screen and see the shadow shrink and become sharp.
Cut small holes in a puppet for eyes and notice that light passes through the holes while the rest stays dark.
Make up a short story and perform it, explaining to the audience why the shadows change size.
What you should see
Clear dark shadows appear on the paper screen. The same puppet gives a large soft shadow near the torch and a small sharp one near the screen, which proves that light travels in straight lines.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why does a shadow form?
Because the object blocks the light, and light cannot bend round it.
2How can you make the shadow bigger?
Move the puppet closer to the torch.
3Why does light pass through the butter paper?
Butter paper is translucent: it lets light through but scatters it, so you see the shadow but not the puppet.
4Does a transparent sheet make a shadow?
Hardly any, because light passes straight through it.
Take it further
Use two torches of different colours from two sides and see coloured, overlapping shadows.
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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