01
Sunlight arrives at nearly one angle
The Sun is so far away that its rays are almost parallel across a field.
Mathematics · 20 minutes
Measure a tree without climbing it
A metre stick and a tree stand in the same sunlight. Predict what stays the same when both shadows stretch or shrink.
Keep this question in mindHow can a small shadow measure a tall tree?
01
Notice the problem
A reachable triangle measures an unreachable height.
The stick and the tree share the Sun's angle, so their height-to-shadow ratios match.
One stick. One shadow.A reachable triangle measures an unreachable height.
The stick and the tree share the Sun's angle, so their height-to-shadow ratios match.
02
Three things to notice
Look at these three ideas.
Each picture shows one part of the question. You will test the ideas next.
02
Height and shadow make a triangle
The upright object and its shadow are two sides of a right triangle.
03
Matching triangles share a ratio
In the same sunlight, height divided by shadow length is the same for the stick and the tree.
03
Your prediction
What should happen to the height-to-shadow ratio when the Sun moves lower?
Choose what you think will happen. It is fine to be wrong. The experiment will help you find out.
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