When a person shuffles their feet on a carpet and then touches a brass doorknob, they may get an electrical shock. If there are enough extra electrons then the force with which those electrons push each other away may be enough to make some of the electrons jump across a gap between the person and the doorknob. The length of the spark is a measure of voltage or "electrical pressure." The number of electrons that move from one place to another per unit of time measured as amperage or "rate of electron flow."