Human hair is made of a protein called keratin, which is shaped like a coil. The coil can be stretched under certain circumstances—for example, when keratingets wet, the coil unwinds and the strand of hair actually gets straighter andlonger (think about your own hair after a shower). When the keratin in the hairdries again, the coil twists up again, making the length of the strand of hairshorter.
Because hair is able to change so dramatically whenit is wet or dry, you can use a strand of hair to build a device called a hygrometer, which measures the humidity ofthe surroundings.
Does humidity have an effect on the physicalappearance of human hair?
A strand of hair will lengthen or contractdepending upon the humidity of the surroundings.
• 2 pieces ofcardboard: one at least
2 inches (5cm) long, the other at least 10 inches (25 cm) long
• A pair ofscissors
• A penny
• A containerof Superglue
• A longstrand of hair least
8 inches (20cm) long
• A pushpin
• A piece ofStyrofoam about an inch square
• A pencil
• A hair dryer
• Adultsupervision (to use the hair dryer)
• The news, anewspaper, or the Internet
(to check the day's humidity level)
1. Using the smaller piece ofcardboard, cut a triangular pointer wide enough that the penny will fit on it. Glue the penny in place using Superglue. Cut two small slits into the pointer, as shown opposite.
2. Wrap one end of the strand of hairaround the pointer at the slits. Superglue the hair in place.
3. Using the larger piece ofcardboard, cut two small slits about half an inch (1.25 cm) apart along oneside.
4. Position the pointer on theopposite side of the cardboard from the slits. Use the pushpin to attach thepointer to the large piece of cardboard. Secure the pushpin with the smallpiece of Styrofoam, as shown below.
5. Pull the opposite end of thestrand of hair so that the pointer is horizontal and the hair is stretched toits full length. Wrap the hair around the two slits in the cardboard, makingsure that the hair stays stretched. Glue the hair in place at the slits. With apencil, mark where the pointer is pointing. The completed hair hygrometershould look like the illustration on page 38 (far left).
6. Take a hot shower and bring thehair hygrometer into the bathroom with you. After at least fifteen minutes, use
a pencil to mark where the pointeris pointing. This point represents 100 percent humidity.
7. With an adult supervising you, usea hair dryer directly on the strand of hair for two minutes. After that, use apencil to mark where the pointer is pointing. This point represents 0 percenthumidity.
8. Leave your hair hygrometer outsidein the shade, someplace where it won’t be exposed to rain, snow, or strongwinds. Every day, mark where the pointer is pointing, and record the day’shumidity (you can check this on the news, in the newspaper, or on theInternet).
Did the hair get shorter or longerat 100 percent humidity in the steamy bathroom? How did the hair’s lengthchange when you dried it with the hair dryer? Did the hygrometer change inresponse to the humidity outside?
Display your hair hygrometerduring the science fair. If possible, bring in the hair dryer and show youraudience how the hair shrinks at 0 percent humidity.
Does curly hair work better in thehair hygrometer, or is straight hair better? Make two hygrometers, one with astrand of curly hair and one with a strand of straight hair. Do they responddifferently to humidity?
How well does damaged hair work inthe hair hygrometer? Get a strand of either color-treated or permed hair, buildanother hygrometer, and repeat your experiments.