Light, shadows and reflection
Physics · Key Stage 1 · The School
Light travels in straight lines
Light goes in straight lines. It keeps going until something stops it or bends it. That one rule explains a lot. It explains shadows. It explains mirrors. It explains why you cannot see round a corner. Shine a torch through dusty air and you can see the straight beam yourself.
How we actually see
We see a thing when light BOUNCES off it into our eye. Nothing comes out of your eyes — and lots of people think it does. You can test that. Sit in a room with no light at all. You will see nothing, however hard you look. There is no light to bounce.
Shadow size
Move the torch closer and the shadow gets BIGGER. The light spreads out, so it hits more of the toy. Move it away and the shadow shrinks towards the object's real size. Try it. Write down what you see at three distances — this is a fair test with one variable, distance.
Stand a toy 30 cm from a torch, with a wall behind it. Predict: will the shadow be bigger or smaller than the toy? Bigger — the light spreads out from the torch. Now measure it: say 12 cm tall. Move the toy to 15 cm from the torch and predict again before looking. Bigger still, and it is: about 20 cm. Halving the distance to the light roughly doubles the shadow, and predicting before measuring is what makes it science.