Einstein Science Reporting for Kids
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23-Jun-2011

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Static electricity revamped: A new take on bad hair days



An example of contact electrification: Rubbing a balloon on hair.
[Image Science/AAAS]

Everyone is familiar with pulling off a wool hat or rubbing a balloon on your head, only to find your hair sticking up like a porcupine. But the age-old explanation for this bad hair day phenomenon, caused by static electricity (which is generated by what scientists call "contact electrification"), turns out be inaccurate, a new study in the June 23 issue of Science Express shows.

Most of us learn in elementary school that opposites attract. It is commonly believed that rubbing causes electrons (particles that carry positive and negative stuff or "charge" that forms atoms) to transfer from hair to a wool hat or balloon, making the balloon uniformly positively charged and the hair uniformly negatively charged.

These two opposite static charges are strongly attracted to each other, and this desire can be seen by pulling a balloon or wool hat slowly away from a person's head, making their hair stand up. Or so scientists thought.

Here, Bartosz Grzybowski and colleagues show that one of the most basic assumptions about contact electrification is wrong. Using a scanning technique that pokes over the microscopic hills and valleys of the material's surface and vibrates differently over differently charged regions, the researchers took a closer look at the charge on objects that were rubbed together.

Surprisingly, they found that both objects have random patches of positive and negative charge, even though they each acquire a different overall net charge.

In other words, instead of one uniform charge for each material, a mosaic of charge actually exists, with islands of positive and negative charge present on both materials.

One surface is positive because it has more positive patches than negative patches, while the other surface is negative because it has more negative patches than positive patches, the authors explain.

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A related video is available at: http://media.eurekalert.org/scipak/gallery/images/2011-06/video_grz.mov