# Describe using a ruler to measure the height of a tree on a sunny day.

1. Measure your height.

2. Determine the length of your shadow. Use a tape measure or a 1-meter ruler to measure the distance from your heels to the top of the shadow you cast.

3. Measure the length of the tree’s shadow. Using a tape measure, determine the distance from the base of the tree to the top of its shadow.

4. Add 1/2 of the tree’s width to the length of the tree’s shade. Most trees grow vertically, in which case the top of the tree is in the middle of the trunk. Therefore, when determining the total length of the shadow, 1/2 of the diameter of the tree trunk should be added to the measured distance. This is due to the fact that the shadow from the very top of the trunk is blurred and practically invisible on the ground.

5. Based on your measurements, calculate the height of the tree. Earlier you measured three quantities: your own height, the length of your shadow, and the length of the shadow cast by the tree (including 1/2 of the trunk width). The length of an object’s shadow is proportional to its height. In other words, the length of your shadow divided by your height equals the length of the tree’s shadow divided by the height of the tree. Using this equality, you can find the height of the tree.