Light and shadows · Grade 4
Light travels from a source in straight lines. When it hits an opaque object it is blocked, leaving a shadow the same shape as the object. We see things because light from a source bounces off them into our eyes – our eyes do not send anything out. Shadows change size with the position of the light, and length with the time of day.
Key facts
- Light sources (the Sun, flames, bulbs, screens) make their own light; the Moon and most objects only reflect it.
- Light travels in straight lines, very fast: about 300,000 km every second.
- Transparent: lets light through clearly. Translucent: lets some through, blurred. Opaque: blocks it, making a shadow.
- Moving an object closer to the light makes its shadow bigger.
- Outdoor shadows are shortest at midday, when the Sun is highest, and point away from the Sun.
- Never look directly at the Sun – it can permanently damage your eyes.
Worked examples
Example 1
At the same moment, a 1 m stick casts a 1.5 m shadow and a tree casts a 9 m shadow. How tall is the tree?
Answer: 6 m