Static electricity
Static electricity causes a boy’s hair to stand on end
Image from
The Reasoner 
When electrons build up on an object, the object becomes charged with static electricity until the electrons are able to jump to another object placed nearby.
The object that is charged with the static electricity could be a car, a ruler, or even a human body. Any object that can conduct electricity can become charged in this way.
Hair-raising!
Ever wondered why sometimes your hair stands up and crackles when you run a brush or comb through it?
Yes, it’s static electricity at work again.
When you brush your hair on a dry day (or after using a hairdryer), the brush collects negative charges from the hair. This means that your hair now has more positive charges than negative charges.
When your hair has more positive charges, each positively charged strand will try and "push" away from other strands with positive charges. This happens because electrical charges that are alike will repel, while electrical charges that are the opposite of each other attract.
It can work the other way around too. As long as when electrons are moved to or from an object, that object becomes charged. So for instance, if a rod is positively-charged and is placed near your hair, it will now cause the electrons in your hair to move towards the end of the hair. Your hair will become attracted to the positive-charged rod, making it stand up.
