How Shadows Form
Recognise that shadows are formed when light from a source is blocked by an opaque object, and find patterns in how shadow size changes
What a learner can do afterwards
- Explain that a shadow forms because an opaque object blocks light from reaching a surface
- Describe the pattern with a spreading torch beam and wall fixed: moving the same object nearer the torch without turning it makes a larger shadow
- Predict a shadow's outline from the light's position, and compare shadow size while keeping the torch and wall fixed and not turning the object
1 · Read
You have tested materials that block light. Transparent and translucent sheets let light through. An opaque sheet blocks light passing through it. Behind an opaque object, part of a surface receives less light from the source. This darker area is a shadow. With no light at all, there is no light to block.
Mia aims a small battery torch at a wall and puts an opaque toy dinosaur between them. The toy blocks some light paths to the wall. A darker outline appears there. Other room light may still reach that area. The shadow does not have to be completely black.
Keep a small torch and wall fixed. Use a spreading beam and one toy without turning it. Nearer the torch gives a larger shadow; nearer the wall gives a smaller one. Change only position. Also turning the toy or moving the torch prevents you from separating their effects.
A shadow follows the outline seen from the light's position, not the object's painted colours. Turn a flat card from its broad side towards its edge: its shadow becomes narrower. A ball lit straight towards a flat wall makes a roughly round shadow. To compare sheets' light blocking, use equal sizes in the same position.
A shadow is a darker area where light is blocked. With a spreading torch beam and wall fixed, moving the same toy nearer the torch without turning it makes a larger shadow.
Readings and flashcards about testing shadow position and outline changes, written for this dataset.
More to read
Test position without turning
Ask an adult to help you aim a small battery torch with a spreading beam at a wall. Put an opaque toy between them. It blocks some light paths and leaves a darker area on the wall.
Keep the torch and wall fixed. Move the toy nearer the torch without turning it. Its shadow becomes larger. Move it nearer the wall without turning it. Its shadow becomes smaller.
Test one toy at a time. A second toy could block light from reaching the first. If you turn the toy as well as move it, you have changed two things and cannot separate their effects.
The shadow may still receive other room light. It need not be completely black. Keep the torch away from eyes.
Test turning without moving
Make a flat cardboard circle with adult help. Hold it between a small battery torch and a wall. Start with the broad side facing the torch.
Keep the torch, wall and card's position fixed. Turn the card so its edge faces the torch. Its shadow becomes narrower. The outline facing the light has changed even though the card has not moved nearer the light or wall.
A shadow follows that outline. It does not copy the colours painted on the card. Turning a flat object and moving it are different tests. Change one thing at a time so you can explain the result.
Use a battery torch away from eyes. Do not use the Sun for this test or look directly at it.
2 · Watch
Take it off screen
Where it sits
Learn first
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.