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# Curly: What Makes Hair Curly?

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Source:
Author: Janice VanCleave

### Problem

What makes hair curly?

### Materials

• Scissors
• ruler
• sheet of typing paper
• pencil

### Procedure

1. Cut a strip of paper 1 inch (2.5 cm) wide and 6 inches (15 cm) long.
2. Hold a pencil in the hand you write with.
3. Hold one end of the strip of paper between the finger and thumb of your free hand.
4. Place the pencil under the paper next to your finger, and slide the pencil down the paper with the strip tightly sandwiched between the pencil and the thumb of your writing hand.
5. Press the paper against the pencil with your thumb as you move the pencil down the paper strip.
6. Observe and record the shape of the paper strip.

### Results

The paper curls toward the side of the paper rubbed by the pencil.

### Why?

You probably think that paper is a flat surface. However, when you view it through a microscope, you can see the many fibers that make up the paper stick up and form hills and valleys across each sheet. Rubbing the paper causes these fibers to flatten out on the rubbed side. The paper, like a strand of hair, curls because one side is slightly flatter. The paper or hair strand will turn, or curl, toward the flatter side. Cross sections of hair strands reveal that straight hair is round and curly hair has an oval shape. The curlier the hair, the flatter is the cross-section view. One side of the hair strand must be slightly more flattened to cause the hair to curve around, thus forming spirals in the hair strand. The curls bend toward the flatter side of the hair strand as did the curls in the paper strip.

### Let's Explore

Does the paper strip always curl toward the flatter side? Turn the curled paper over and rub the pencil down the opposite side several times. Explain why the first rubbing straightens the paper and continued rubbings cause the paper to curl in the opposite direction. Science Fair Hint: Photographs showing the paper before and after the rubbings along with the paper strip and the explanation can be used as part of a project display.

### Show Time!

1. Can a strand of straight hair be curled by rubbing one side? With the permission of a friend with straight hair, borrow a long strand of hair. About 2 inches (5 cm) from the end, sandwich the hair strand between your index finger and thumbnail of your writing hand. Hold the short end with your free hand and move your nail down the hair. Observe the shape of the hair. Display the strand by taping one end to a sheet of paper. Use this and an explanation of why the hair changed its shape as part of a project display.
2. Would the texture of the hair affect it being curled? Use samples from different people and repeat the procedure of moving your thumbnail down the hair strand. Display all of the different samples along with explanations of why they each changed shape and a conclusion stating if texture affects the curling of hair.
3. Why does the kinky shape of wool make it good for making clothing? Hold one end of a 12-inch (30 cm) piece of wool knitting yarn in one hand. Pull on the opposite end with the other hand, and then let go. The piece stretches and springs together much like a rubber band. Untwist the strands of yarn and then let go. The strands spring back together. Make a diagram of the yarn to go with an explanation stating that woolen clothing feels comfortable because it stretches when you move and does not wrinkle greatly because the wool tends to spring back to its original shape.

### Check It Out!

Hair from a horse's tail is very straight and is used to make paintbrushes. Discover more about the uses of straight and curly hair from animals. Display articles or pictures of items that use animal hair.

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