Light, shadows and reflection
Physics · Key Stage 1 · The School
Light travels in straight lines
Light goes in straight lines until something stops or bends it. That single rule explains shadows, mirrors and why you cannot see round corners. Shine a torch through a dusty beam of air and you can see the straightness with your own eyes.
How we actually see
We see an object when light BOUNCES off it and enters our eye. Nothing comes out of your eyes — a surprisingly common misconception, and one worth testing: in a completely dark room you see nothing at all, no matter how hard you look, because there is no light to bounce.
Shadow size
Move the torch closer to the object and the shadow gets BIGGER, because the spreading light hits more of the object and misses more of the screen. Move it away and the shadow shrinks towards the object's real size. Try it and record 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.