In 600 BC, the Greek philosopher Thales[1] observed that some combinations of materials have more potential to make sparks fly than others. Materials can be catalogued in order of their tendency to become charged, from positive to negative. The lower an item sits on the list, the more likely it will attract more electrons and become negatively charged. Rubbing objects far from each other on the list creates a bigger charge than objects closer together. For example, polishing a glass plate with a silk scarf electrifies the scarf so that it acts like a magnet.
When you stride across a wool carpet in leather shoes, your shoes pick up extra electrons from the carpet with each step. By the time you lift your foot up off the ground, the electrons will have spread around your entire body, giving you a negative charge. The next time you put your foot on the carpet, your shoe doesn’t have any extra electrons, but your head might. So more electrons make the leap to your foot.
“As you keep walking across the floor, you become full of electrons,” said Todd Hubing, from the Electromagnetic Compatibility Laboratory at the University of Missouri-Rolla. “Eventually more electrons don’t want to come up on you because you’re so charged up. You end up with a high voltage, about 20,000 to 25,000 volts.” That’s serious power at your fingertips, considering a normal electrical outlet on the wall is only around 100 volts[2] of electricity.
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