Ask Ollie
Tree Height Detectives
Here's one to try together!
Find out how tall a tree is without climbing it, using just a stick and your shadow!
Reviewed by our team.
Safety first
- walking backwards may cause tripping or falling on uneven ground
- possible obstacles outdoors
- do not look directly at the sun when working with shadows
What you need
- Paper, 1 sheet
- Tape measure, 1
- Pencil, 1
How to do it
Grown-up prep: Pick a sunny day and a tree with flat, clear ground around it. Check the ground for holes, roots and trip hazards. Shadow work works best mid-morning or mid-afternoon.
- Look up at the tree and guess its height. Write it down. Ask: How many of you, standing on each other's heads, do you think the tree is?
- Hold the stick upright at arm's length in front of you.
- Walk backwards until the stick matches the tree.
- Count your steps from where you stand to the tree.
- Measure that same distance with the tape measure. Ask: What do you think this distance tells us about the tree's height?
- Measure your own height, then your shadow length.
- Quickly measure the tree's shadow, from its base to the tip.
- Divide the tree's shadow by yours, then multiply by your height.
- Compare your two answers and your first guess. Ask: Why might the two answers be close but not exactly the same?
- Now measure another tree or building! Which one will be the tallest you find?
Play it again
- Tree league: measure 5 trees and rank them from tallest to shortest.
- Building check: use the shadow method to measure a lamp post, a fence or the side of a house.
- Time travel: measure the same tree's shadow in the morning and afternoon. Does the height answer stay the same?
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