Feet and Inches

Even the bones of the feet can tell you a lot about the person they came from. Try the following investigation to see what feet reveal about a person’s height.

Materials

- tape measure
- pen or pencil
- paper
- calculator
- several helpers

Procedure

NOTE: This activity works if the helpers are older people who have stopped growing, rather than young children.

1. Have each helper remove his or her shoes. Use the tape measure to measure the height of each helper in inches (cm). Write each person’s name and height on the paper.
2. Have each helper stand with his or her left heel against the wall and perpendicular to the wall.
3. Carefully measure the length in inches (cm) of each person’s left foot, from the wall to the big toe. Write that information next to each person’s name and height.
4. Look at the numbers. Do you notice a pattern?
5. Use the calculator to divide the length of each person’s left foot by his or her height. Multiply the result by 100. What result do you get?

More Fun Stuff to Do

Have a helper stretch his or her arms out sideways as far as they can go. Measure the distance from the tip of the middle finger on one hand to the tip of the middle finger on the other. Compare that measurement to your helper’s height. What do you notice?

Explanation

The results of your calculation in step 5 should all have been approximately 15. For example, if a person is 63 inches (160 cm) tall and his or her left foot is 9 ½ inches (24 cm) long, the result would be 9 ½ inches (24 cm) divided by 63 inches (160 cm) times 100 equals 15. This means that the length of a person’s foot is about 15 percent of his or her height.

If a forensic scientist had to identify a person using only the bones of the foot, he or she could approximate the height of that individual using this technique. This is because the bones in the body grow at certain rates and are in proportion to one another.

Thus, in the More Stuff to Do section, the distance between the tips of the middle fingers when the arms are out stretched is the same as a person’s height. As a person’s grows taller, the feet grow bigger and the arms grow longer at the same time. By the time he or she is full grown, foot length and arm span will give approximate values for height.
These values are not always true as people grow. The ratio of one body part to another will change greatly throughout childhood. For example, the circumference of the head of a newborn, is about 25 percent of the baby’s height, while that of an adult is only about half that value.