Light and shadows · Grade 5
In Grade 5 you learn: shadows during the day, light travels in straight lines, and working out the size of a shadow.
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 travels in straight lines, very fast: about 300,000 km every second.
- Outdoor shadows are shortest at midday, when the Sun is highest, and point away from the Sun.
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
Example 2
A 6 cm puppet is 20 cm from a small flashlight. The screen is 80 cm from the flashlight. How tall is the shadow?
Answer: 24 cm