Light and shadows — Physics, 7–10 years
Light travels from a source and helps us see. When an object blocks some of it, a shadow appears.
What light and shadows are
Light travels from a source, such as the Sun, a lamp or a candle. We see an object when light reaches it and some light comes into our eyes. A shadow is the darker space behind an object that blocks the light.
Why shadows change
People needed to tell the time before clocks were common, so they watched how the Sun made shadows move. The shadow points away from the light source. Moving the lamp or the object changes the shadow’s direction, length or position.
Making a shadow
Place a torch, a toy and a wall in a line. First put the toy 20 centimetres from the torch: its shadow is large on the wall. Move the toy to 40 centimetres from the torch, keeping the wall still. The shadow becomes smaller because the toy blocks a narrower part of the torch’s spreading light.
A common mistake
A shadow is not a painted dark shape stuck to an object. It is a place where less light arrives, so it can move and change size. It is easy to think it belongs to the object because it follows the object when the light and wall stay still.
Where it is used
Sundials use a stick’s shadow to show changing time, although a clock is more exact. Cameras and phones use carefully controlled light to make pictures. Theatre performers also use lamps and screens to make silhouettes, giant shadows or playful shapes.
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