Why does electricity make hair stand up?

Answer 1

Static electricity does funny things. First, it's a form of contact electrification, and it has to do with the moving or movement of charges to create an imbalance. In this phenomenon, electric charges (electrons) are fed onto an object or drawn off that object. This will give it an overall charge, and it will be either negative or positive, respectively. And when the charges are moved, the charge on the object will equalize. It won't concentrate (generally) but will "spread out" over the surface of the object that is charged (but there will be some charge concentration at any part of the surface that has sharp "points" to it). So we've got a person charged up with, say, a whole bunch of extra electrons. Do you have the picture? Good. Let's jump. The zillion or so "extra" electrons we charged the person up with spread out over the person. Lots of them are on the person's hair. Remember the basic law of electrostatics about how opposite charges attract and like charges repel? Guess what all those electrons in the person's hair are doing. They're pushing each other away. And because the hair strands aren't really massive (heavy), the hair strands are pushed apart and away from the person. The hair will stand up to get away from the person, and the strands will push away from each other separating those strands. The charges are doing this as the move to equalize themselves over the surface of the charged object (the person). When a person's body is charged, the charges distribute themselves over the outside of the person (to minimize charge density). This includes the hair. And the hair, because it is light and can move freely, will stand up to get away from the person, and the strands will move away from each other as like charges repel. The charges always move around to "minimize" charge density 'cause they don't like each other. This spreads them out over the object charged and gives rise to the movement of the hair.