Have you ever taken off a woollen jumper and felt a slight shock or felt your hair stand on end? Or have you ever felt a spark when you walked on a carpet and touched something metallic?
This all has to do with a fascinating phenomenon we call electrostatic friction. Although it sounds like magic, it's actually science. And once you understand it, you'll be able to impress your friends with your electrical knowledge.
First, let's talk about the basics: atoms
To understand electrification, we first need to know how things are made.
Everything around us, including us, is made of tiny particles called atoms. Atoms are so tiny that they can't be seen with even the most powerful microscope, but they're everywhere.
An atom has three main parts:
- Protons, which have a positive charge (+).
- Electrons, which have a negative charge (-).
- Neutrons, which have no charge; they are neutral.
Normally, atoms have the same number of protons and electrons, which means they have a neutral charge. That is, they are not electrically charged.
What happens when we rub two objects?
When we rub two materials together, such as a balloon and a sweater, something interesting happens to the electrons. Electrons are not "stuck" to their atom like cement; they can move around, especially if they encounter another material that attracts them more.
For example:
- If you rub a balloon against your hair, some electrons from the hair jump to the balloon.
- This leaves the balloon with more electrons (negative charge) and your hair with fewer electrons (positive charge).
Now you have two things with opposite charges. The balloon is negatively charged and your hair is positively charged. It is this exchange of electrons that we call friction electrification.
What about these loads?
Now that we have electrified the balloon and hair, things get fun.
You've probably heard that opposites attract, right? The same goes for electric charges:
- Opposite charges (positive and negative) attract.
- Equal charges (positive and positive or negative and negative) repel each other.
That's why when you bring the charged balloon close to your hair, the strands of hair appear to "chase" the balloon. The positively charged hair is trying to get closer to the negatively charged balloon.
Examples of electrification by friction
Where else can we see electrostatic friction? Here are some interesting examples that have surely happened to you:
-
Sticky Balloon
After rubbing a balloon against your hair or a sweater, you can stick it to a wall. Why does this happen? The wall has a neutral charge, but the negatively charged balloon "pushes" electrons away from the wall, leaving the surface with a slight positive charge. That's why they stick! -
Hair on end
When you take off a wool hat, the friction between the hat and your hair causes some electrons to be transferred. This causes each hair to have the same charge, and since like charges repel each other, your hair stands up in all directions. -
Attracting bits of paper
If you rub a pen or plastic ruler against your clothes, you may attract bits of paper. This happens because the plastic becomes electrically charged and attracts the neutral particles in the paper. -
Sparks on the carpet
On dry days, walking on a carpet with socks on can cause you to become electrified. When you touch something metallic, such as a door handle, this accumulated charge is quickly discharged, creating a spark.
Why does this happen more in winter?
You may have noticed that these discharges and electrical effects are more common when it is cold, especially in winter. This is because cold air is drier. Humidity in the air helps the charges to dissipate quickly, but in a dry environment, the charges build up and the effects are more visible.
Materials involved in electrification
Not all materials are electrified in the same way. Some are more prone to losing or gaining electrons. Here are some examples:
- Materials that tend to lose electrons: human hair, wool, glass.
- Materials that tend to gain electrons: plastic, rubber, silk.
This means that if you rub a plastic comb against your hair, the comb will gain electrons (become negatively charged) and your hair will lose electrons (become positively charged).
And what about metals?
Metals are conductors, which means they allow electrons to move easily through them. Because of this, they don't get as electrified when rubbed. Instead of building up charges, they quickly discharge them into the ground or another object. That's why we touch something metal and feel a spark: the metal is helping to balance the charges.
Experiments to try it yourself
The best way to learn science is by experimenting! Here are some ideas for playing with electrostatic friction:
- Balloon and confetti
- Rub a balloon against your hair or a sweater.
- Bring the balloon close to small pieces of paper and watch how they lift up and stick to the balloon.
- Crazy hair
- Rub a plastic comb against your hair.
- Hold it close to a friend's hair (carefully) and see if the strands lift up towards the comb.
- Stick a balloon to the wall
- Charge a balloon by rubbing it with a sweater or your hair.
- Stick it to a dry wall and see how it stays there.
- Carpet spark
- Walk on a carpet while wearing wool or cotton socks.
- Touch something metal, like a door or a faucet, and feel the shock.
Is it dangerous?
Don't worry! The small shocks we feel when we get electrocuted are not dangerous.
However, static electricity can also be responsible for more serious things. For example, at a gas station, a spark of static electricity can be dangerous if there are gasoline fumes. That's why it's important to follow safety rules in places like these.
The useful side of friction electrification
Although it may sometimes seem like a mere curiosity, electrostatic friction has practical applications. For example:
- Electrostatic air filters: Use electrical charges to trap dust particles in the air.
- Laser printers: Use electrical charges to attract toner to the paper.
- Adhesive tapes: Some use static electricity to improve adhesion.