Photo by Mathew Wilson
Photo by Mathew Wilson

Note:  This is the part of a series of posts about science activities to be done in the bathroom – the lav-oratory if you will.  

Have you ever taken a bath or spent hours in the pool only to find your fingers and toes are all wrinkly? For a long time people thought that skin absorbing water caused the wrinkles, but if that’s the case, why doesn’t your whole body get wrinkly? And why do we get wrinkly in the first place?

Since the 1930’s scientists knew that finger wrinkly was controlled by your body’s autonomic nervous system, the system that also controls breathing, heart rate and sweating. They noticed the people with nerve damage do not get wrinkly fingers in the water. Finger wrinkling is actually caused by blood vessels constricting below the skin.

One theory about the reason our fingers wrinkle when they get wet is that, like the treads on a tire, it increases your grip on wet objects. Scientists have  gotten mixed results as to whether wrinkled fingers really do make it easier to hold on to wet objects. What do you think?

Try it out!

  1. Fill a large bowl (or sink or bathtub) with warm water. Hold both hands in the water for 20-30 minutes until your fingertips are completely wrinkly.
  2. Place 10 marbles in one of the bowls. Place the bowl of marbles on one side and an empty bowl on the other side.
  3. Get your stopwatch ready and time how long it takes to move the dry marbles, one at a time, from one bowl to the other. In between  transfer the marble from one hand to the other.
  4. Pour water into the bowl with the marbles. Soak your hands for a few more minutes to keep them wrinkly.
  5. Again, time how long it takes to move the wet marbles from one bowl to the other in the same way.
  6. Take a break so your fingers dry out and become un-wrinkly again. Repeat the experiment with smooth fingertips, and wet and dry marbles.

Under which conditions did you move the marbles the quickest?  Get some friends or family members to try it too and take an average.

Check out the Science Friday story with another science project idea.

Eureka! Wrinkly Fingers
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