# How Strong Is Your Hair?

How Strong Is Your Hair? – STEM Activity

## Introduction

Have you ever wondered how strong hair is? When we talk about our hair we usually discuss color, length or texture. But what about hair strength? If you look at a strand of hair, it looks like a very thin string. In fact, it is on average only about 0.1 millimeters thick. It doesn’t seem like such a thin string could withstand much force. How much weight do you think a single strand of hair can carry? In this activity you will put a hair to the test and find out. You might be surprised by your results!

## Materials

• At least one hair strand (at least 5 centimeters long). This can be collected from a brush or comb or elsewhere.
• Pencil
• Two stacks of books or two same-sized boxes
• Paper clip
• Tape
• Small plastic bag
• Small items to use as weights (such as pennies, marbles, etcetera)
• Scale
• Optional: additional strands of hair—including some from different people

## Prep Work

1. Tie one end of a hair strand securely around the middle of the pencil. If making a knot is too difficult, you can tape the hair to the pencil.
2. Attach the other end of the hair strand to a paperclip (using a knot or tape).
3. Hook the paperclip through the top of one side of the small plastic bag.
4. Test whether the hair holds on to the pencil and bag by pulling on both ends slightly. If the hair comes loose, use more tape to secure the hair.
5. Stack two piles of books or boxes to the same height—tall enough to accommodate the length of the hair and plastic bag. Place the stacks next to each other leave a gap between them that is the right size so the pencil balances across them and the bag hangs freely.

## Instructions

1. Before you start your test, guess how much weight the hair will able to carry.

 How many pennies or marbles do you think it will take to break the hair?
2. Take one of your weights (pennies or marbles) and carefully place it into the plastic bag.

 Does the hair break?
3. If the hair is still intact, gently add another penny or marble to the bag.

4. Continue to add weight to the bag. Inspect the hair carefully after adding each weight.

 How does the hair hold up with increasing weight?
5. Once the hair breaks, place the plastic bag, including the pennies or marbles that are inside, on the scale.

 How much weight was the hair able to carry? Was it more or less than you predicted in the beginning?

## Cleanup

1. Remove all the used materials to where they belong.

## What Happened?

How much weight was your strand of hair able to carry? Did your results surprise you? Although a single strand of hair looks very thin and fragile, it can carry a weight of up to 100 grams. This is due to the three-layered structure of the hair shaft and to the strong keratin fibers that make up the middle layer, or the cortex, of the hair strand. How many grams would you estimate all of a person’s hair could hold?

## Digging Deeper

Did you know that an average person’s head has about 100,000 hairs? Each one of these hairs grows out of a hair follicle, which is a tunnel-shaped structure in the outer layer of our skin. You might have noticed that at its root a hair sometimes has a whiter and softer texture than the rest of the hair. This part of the hair, which is usually beneath the skin, is called the hair bulb. It is the living portion of the hair and is responsible for hair growth. The other part of the hair, which we see growing out of our skin, is called the hair shaft.

The hair shaft is primarily responsible for our hair’s strength. You might be surprised to hear that although a hair shaft is on average only 0.1 mm thick, is made up of three different layers. The innermost layer at the hair’s center is called the medulla. It is almost invisible and very soft and fragile. The middle layer is the thickest layer and is called the cortex. Much of its strength comes from a material called keratin. Keratin is also found in our fingernails, as well as animals’ feathers, hoofs and claws. In this layer, the keratin is arranged in rod-like bundles—alongside fats that add additional structure. The cortex also houses the melanin pigments that give our hair its color. The outermost layer of the hair shaft is called the cuticle. This layer is formed by flat, overlapping layers of cells that form scales, similar to fish scales, which strengthen and protect the hair shaft. Together these three layers create a very strong hair fiber.

## For Further Exploration

• Repeat the same test with hair from different people. Which hair is the strongest?
• Instead of using one strand of hair, try the test with two or more strands of hair tied in parallel. Can two strands of hair carry double the weight?
• Find out if hair texture makes a difference. Does curly hair or straight hair carry more weight?