by Lee Falin, PhD
It’s that time of year when some of us develop a dread of touching doorknobs. The cooler months of fall and winter seem to bring an increase to the annoying little shocks that we sometimes feel when touching metal objects. But why do these little demons of pain seem to afflict us only in the colder months? Let’s take a look at the science behind these shocks to find out.
Sponsor: With lynda.com, you can learn software, business, and creative skills to achieve personal and professional goals. Try lynda.com free for 7 days by visiting lynda.com/everyday
Every time you take a step, the bottom of your shoe forms a series of chemical and mechanical bonds with the surface of whatever you’re stepping on. As you might remember from my episode on Atomic Bonds, electrons tend to move between atoms in an attempt to satisfy the needs of greedy atoms. This means that when your shoe forms a temporary bond with the floor, some electrons are transferred between the two.
When you lift up your shoe to take another step, some of those extra electrons it picked up remain behind, giving it an electric charge. Because your shoe is an insulator, this electrical charge doesn’t have anywhere to go. That’s why it’s called static electricity. It just hangs out on your shoe, getting stronger with every passing step.
Don’t Let the Door Hit You on the Way Out!
Eventually you might realize that you’ve had enough of this shuffling around on the carpet and decide to go outside. As you reach for the doorknob, the electrical charge that has built up around your body sees its chance to escape. (Remember that an electrical charge represents an imbalance of electrons.) Those extra electrons know that they aren’t wanted and so when you touch a conductive surface, such as a metal doorknob, they leave in a hurry.
Unfortunately for you, the way they leave is via an electrostatic discharge, often of several thousand volts. This creates a rather painful shock, and can even damage sensitive electronic devices. That’s why computer technicians often wear anti-static wristbands that help get rid of excess electrons before they can build up a charge strong enough to cause any damage to their gadgets. My colleague Tech Talker could tell you a lot more about that.
Of course things other than your shoes and the carpet can cause static electricity. You’ve probably seen experiments where combs are rubbed with wool socks, or the slightly less popular experiments where cats are rubbed with balloons. Both of these examples seem to generate static electricity through friction, but it isn’t the friction that causes the build up of static charge, it is the rapid formation and breaking of mechanical and chemical bonds of the two surfaces.
You might be wondering: In the cat example, is it the hapless cat or the balloon that is getting the extra electrons? In this case, it’s the balloon that picks up the extra electrons. You can determine that by looking at their relative placement on the triboelectic series.
If you take a group of materials such as balloons, shoes, cat hair, etc. and put them in order by their likelihood to either gain or give up electrons during contact with each other, you have created a triboelectric series. If you take any item on that list and rub it against a second item lower down on the list, the second item will gain electrons from the first item. However, if you rub the first item against an item higher on the list, the first item will gain electrons. It’s important to note however, that a static charge builds up on both items. The item that gains extra electrons has a negative static charge while the one that loses electrons has a positive static charge.
That’s Not Jack Frost Nipping at Your Nose
So now that you understand how static electricity forms, and the painful way it tends to dissipate, we can turn our attention to the fact that this tends to occur more often in the winter months. Is it that static electricity has something against the holiday season?
Turn out, it doesn’t actually have anything to do with the holidays at all. The problem is that in the winter the air is typically less humid.
Remember we said that the static charge builds up on your shoes, balloon, or your cat’s fur because since these items are insulators, the extra electrons don’t have anywhere else to go. In warmer weather, the air is more humid. The water in the air acts as a conductor and transfers the excess electrons away from the charged objects before they can build up enough of a static charge to cause a shock.
That’s why you tend not to get shocked in the warmer months, or very humid conditions.
Do Try This at Home
As a fun experiment, go into your bathroom on a cold, dry winter day and rub your hair for a few seconds with a balloon and notice how the static charge affects your hairdo. Now, turn on the shower and set the temperature high enough so that it generates a lot of steam. Wait a minute or two until the bathroom is really steamy and try again. The excess moisture created by the hot shower should prevent the static charge from building up enough to affect your hair.
That’s all of the shocking facts we have time for today. If you have more questions about this episode, or ideas for a future episode, send me an email at email@example.com, or send me a message on the Everyday Einstein Facebook page.
Meanwhile, if you’re confused about whether the effects of electricity affect you or if the affects of electricity effect you, you might want to pick up a copy of Grammar Girl’s Quick and Dirty Tips for Better Writing. It’s a great book and makes a great stocking stuffer for your grammatically-challenged loved ones.