How strong is a strand of your hair?

By Marshall Brain


http://youtube.com/watch?v=xnoAXwKhLtY
http://video.google.com/videoplay?docid=1096770616004078949

In the video, we used a stack of books, a strand of hair and some pennies to see how strong hair is. By taping pennies onto a strand of hair one by one, we were able to measure the strength of a single strand of hair.

We used pennies because they are small, standardized and easy to obtain. In the video we calculated that a penny weighs 2.5 grams, and that the strand of hair we used could hold 23 pennies before breaking. Which is pretty amazing!

If you want to try some hair experiments at home, here's what you need:

  • A stack of books
  • A pencil
  • Some tape
  • A handful of pennies
  • A strand of hair
Step 1: Securely tape one end of the strand of hair onto the pencil

Step 2: Wedge the pencil into the stack of books so that the pencil is sticking out and the hair is hanging down (see the video).

Step 3: Securely tape one penny onto the strand of hair and see if the hair can hold it.

Step 4: Keep taping on pennies until the strand breaks.

In our experiment, we managed to tape 23 pennies on before the strand broke. 23 times 2.5 grams is 57.5 grams. In the video, when we actually weighed the stack of pennies, it weighed 62 grams. The tape actually weighed 4.5 grams!

The fact that the tape had weight is important. It means that this might not have been the best way to perform this experiment if you don’t have a scale handy. It would have been better to hang a small cup or bag on the hair and add the pennies one by one to the cup, so that there is no “extra” weight being added.

There are lots of experiments you could try at home. Is straight hair stronger, or curly? Is blond hair stronger, or brown or black? If you get hair wet, does it get stronger or weaker? What about if you dip it in a weak acid like vinegar? If you braid three strands of hair together, is it 3 times stronger? What if you tie a knot in the middle? Have fun performing your own science experiments!