When a material loses electrons it becomes positively charged, and if it gains electrons it becomes negatively charged. When these electrical charges accumulate on the surface and are not a flowing current, it is referred to as static. When positively and negatively charged surfaces come into contact and are pulled apart a spark can result, which we refer to as static electricity.
If hair is combed rapidly on a dry day, electrons can be lost, which positively charges the hair. The comb becomes negatively charged because it gains electrons, and the result can be flyaway crackling hair reacting from static electricity. A person can charge herself by walking across a carpet and then touching a metal object, which will result in a shock.
Objects can gain a stationary electrical charge by contact or induction. An object can become electrically charged when touched by an object that is already charged. This is referred to as a contact charge. During induction, the object is charged when it is in close proximity to an object that is already charged. In induction, the objects do not touch.
Static electricity can pose certain dangers. At the gas pump, the spark from static electricity can start a fire or ignite an explosion. Half of the incidents occur when a person returns to the vehicle after starting to pump gas, and then fails to touch any metal before returning to remove the gas pump nozzle. More than a quarter of the incidents occur when removing the gas cap. To avoid these dangers, always turn off the engine before fueling, and never reenter the vehicle until after you are finished with the gas pump.
Static electricity can be manipulated to make modern devices work. In some copy machines the internal plastic drum is in a charged state. The page to be copied is placed over a piece of glass. The static electricity on the drum causes the dark toner powder to gravitate to the corresponding areas on the copy paper where the picture would be dark. Heating causes the toner to adhere to the paper, and a copy is made.