When Sparks Fly: The Static Menace


Image by Sara Grady, all rights reserved.

It’s a typical, pleasant winter morning in Evanston. The ground is covered with a blanket of wispy snow. The Northern winds blow my scarf like a windsock. I reach for the handle on my car door and zap! I feel the most excruciating “electric shock”. Sparks fly momentarily between my hand and the car door. Unsuccessfully attempting to mask the expletive that escapes me, I begin thinking about what just happened. Why is “winter sparking” or static electricity such a menace, especially in the dry winter months? Can you do something to avoid getting electrocuted each time you reach for the door knob?

To understand this phenomenon, let’s zoom deep into matter. All matter is ultimately made of atoms that consist of 3 types of particles: positive protons, negative electrons, and neutral neutrons. Each atom has an equal number of protons and electrons, making it electrically neutral. When certain materials rub together, though, electrons from one can be transferred to another. This is called triboelectric effect based on the Greek word tribein (meaning 'to rub').

Some materials – like wool and flannel -- are friendly and give away electrons easily. When materials do this, they end up with fewer electrons than protons, making them electrically positive. Other materials – like leather and vinyl -- are more likely to receive extra electrons than give up their own. With extra electrons in tow, these materials become negatively charged.

Whether atoms gain or lose electrons, they always seek to regain neutrality. If they’ve become positively charged, that’s by retrieving the lost electrons or finding other replacements; if they are negatively charged, it means giving away the ones it's collected. This drive to maintain and restore electric neutrality is what makes static discharge a menace.

When you walk on a woolen rug, with each step, the friction between your feet and the rug drives a triboelectric exchange leaving your body negatively charged. Your electron build-up will always take the first escape route back to neutrality. So when you approach a metal door knob, the excess electrons zip from your hand to the obliging knob.

When you get out of a car in the winter, your woolen sweater or jacket rubs against the vinyl car seat. Once again, the friction promotes a negative charge build-up on your body, sometimes reaching thousands of volts. Now you’re super-charged, when you next reach for the metal car door, this voltage difference is enough to cause a sudden discharge through dry, winter air, generating a visible spark.

The dry weather of the cold winter months accentuates the severity of static electricity. This is because humid air contains water vapor, which makes it a better conductor of electricity. Water molecules in the air slowly conduct charges away and prevent a large charge build-up in the first place.

So how do you avoid getting zapped? Give the excess electrons an easy, pain-free way out. When getting out of a car, touch the metal door as you slide out of your seat, preventing the charges from building up in the first place as you will be conducting them away as they’re generated. If you touch the door knob with a metal key first, it gives the excess electrons on your body a conductive pathway and prevents the sudden discharge through the air, protecting your sensitive fingertips. You could also first touch the knob with your knuckles, which have fewer nerve endings (so the same amount of discharge will hurt less).

Static discharge is often sudden and happens when two oppositely charged bodies come near each other. But it doesn’t just happen with metal objects, sometimes it can happen with other people. When charges are unequal, electrons will flow from the person with the greater charge to the person with the lower charge, sending sparks flying. (This zap can be mistaken for a romantic connection, but it is just pure physics! Disappointing as it may be to have that myth busted.)

My unpleasant zap that wintery morning sent me digging deep into static electricity and how to cope with it. Now aware about sudden static discharges, I am always armed with a metal key each time I approach my mortal enemy: the door knob.



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