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Static electricity

Static electricity

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What does it mean for two or more objects to repel each other?

Static electricity

Bad hair day, huh? It’s physics playing tricks on Philip. His sweater gave him electric shock, then he got this weird electric hairdo. Sparks and electricity, just from taking a sweater off -- what’s up with that? To find out, we have to look really really close at Philip’s hair.

Just like any other matter, Philip’s hair is made up of atoms. Here’s a simplified model of one of them. At the centre is the nucleus, which contains protons. Around the nucleus are the electrons. Each of them are charged with tiny amounts of electricity.

The protons have a positive charge and the electrons have a negative charge. Since there is exactly the same number of electrons as protons, the charges balance out. The atom’s combined charge is zero! On a normal day, Philip doesn’t experience any electricity in his hair at all. But this isn’t a normal day.

Watch what happens when Philip pulls a polyester sweater over his head! The atoms in the polyester are rubbed against the hair, and some of the electrons from the hair are rubbed off, and stick to the polyester instead. The protons inside the nucleus are too firmly attached to the rest of the hair, to rub off easily. But those electrons, whizzing around far outside the nucleus, are easy to tear off. And that’s what the polyester sweater does - it steals some of the hair’s electrons!

Now there is an imbalance between the positive and negative charges. The sweater has an excess of negative charges, and Philip’s hair has an excess of positive charges. When pulling his sweater over his head, Philip created static electricity. Static electricity is an imbalance between positive and negative charges. But charges don’t like imbalance at all.

Charged particles want to be where there is just as much positive as negative charge. To fulfil this yearning for balance, positive charges are drawn to negative ones, and negative charges are drawn to positive ones. Opposites attract. When Philip took his sweater off, he upset this balance. Each hair on Philip’s head lost some electrons, and is now positively charged!

And positive charges don’t like to be close to each other, they push away -- they repel. Each hair wants to be as far away from its neighbour as it can. Opposites attract, and like repel. When dealing with charges in physics, this is always the case. The same thing happens with those extra electrons that ended up on the sweater.

They push away from each other, wanting to be as far away from each other as they can. Those negatively charged particles are upset: “It’s over-crowded with electrons in here, we want out!” They yearn for balance, and search for a place with an excess of positive charges. The electrons jump to a better place, where they can even out the charge imbalance. That’s how much charged particles like to be in balance -- their longing is so strong that they will jump through air to reach it. When electrons move to another place, to reduce the imbalance, we say that they discharge.

Static electricity can discharge slowly, a few electrons at a time. Then you won’t notice it. Or it can jump all at once, with a spark. Pull a polyester sweater over your head in a dark room and you’ll see! Waaaah!