Light and shadow
Light always travels in straight lines. If an obstacle gets in its way, light cannot bend round it, so a shadow forms behind the obstacle. A shadow is a place where light does not reach. The size and shape of a shadow depend on the light source and the object. In the morning and evening, when the Sun is low, shadows are long; at midday, with the Sun high up, they are short. Transparent objects (window glass, clean water) let light through so we see what is behind. Non-transparent objects (stone, tree, book) do not let light through and cast shadows.
Experiments: 1) Punch a hole at the same height in three cards, line them up so the holes are in a row and shine a torch through: light passes. Move one card sideways and the light stops — straight line. 2) Shadow theatre: with a torch near a wall make rabbit or bird shadows with your hands. 3) In the morning and at noon draw your shadow with chalk in the yard and compare the lengths. Safety: never shine a torch in anyone’s eyes.