Light and shadows — Physical education, 7–10 years
Light travels from a source, and objects can block it. A shadow shows where light could not reach.
Light travels and objects can block it
Light comes from a source such as the Sun, a lamp or a candle. It travels outward, and an opaque object blocks it, leaving a darker region behind. That darker region is a shadow, not a painted mark on the object.
Why do shadows matter?
Long ago, people used shadows to notice that the Sun changes position during the day. The idea of blocked light explains both a sunny silhouette and why a room becomes dark when its lamp is covered. It gives us a way to predict where light will and will not reach.
Making a hand shadow
Place a torch 30 centimetres from a wall and hold your hand between them. The torch sends light towards the wall, but your hand blocks part of it. Move your hand closer to the torch: the blocked region grows on the wall, so the shadow becomes larger.
A shadow is not always the same size
It is reasonable to think a shadow must be the same size as the object making it. But its size depends on the positions of the light source, the object and the surface. A torch close to the object spreads its blocked light over a larger area of wall.
Shade and sundials
A parasol or tree gives shade because it blocks some sunlight, making a cooler place underneath. Architects use light and shadow when placing windows and roofs. A sundial uses the changing direction of a shadow to show the time, although a clock is more exact.
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