Light and shadows

Your shadow follows you

On a sunny day your shadow walks beside you. In the morning it is long and stretched out, but at lunchtime it is short.

Why does your shadow change? It all comes down to how light travels.

See light being blocked

Light travels from the source in straight lines. When an opaque object is in the way, the light cannot get through, and a dark area forms behind it.

Why shadows change

Materials are transparent (let all light through, like glass), translucent (let some light through, like tissue paper) or opaque (let no light through, like wood).

Only opaque and translucent objects make shadows. A shadow is the same shape as the object's outline.

Move the light source closer to the object and the shadow gets bigger. Move it further away and the shadow gets smaller. When the Sun is low in the sky, shadows are long; when it is high, they are short.

Light source

Something that makes its own light, like the Sun or a torch.

Opaque

Does not let light through.

Translucent

Lets some light through, but you cannot see clearly through it.

Transparent

Lets light through so you can see through it.

Investigate

You need a torch, a toy figure and a wall or large sheet of paper. Do this in a dim room.

1. 1Stand the toy 20 cm from the wall and shine the torch at it from 50 cm away.
2. 2Measure the height of the shadow and write it in a table.
3. 3Move the torch to 40 cm, 30 cm and 20 cm away. Measure the shadow each time.
4. 4Only change the torch distance — keep everything else the same so it is a fair test.
5. 5What pattern do you notice? Write a sentence: “The closer the torch, the…”

Quick quiz

Think about how light travels.

Think about it

People used shadows to tell the time long before clocks.

How could you use a stick and the Sun to tell the time? What might go wrong?