Why Do We Get Static Shocks?

When two different materials rub together, electrons transfer from one surface to the other — a process called triboelectric charging. Walking across a carpet in rubber-soled shoes, for example, strips electrons from the carpet onto your body, building up a negative charge of thousands of volts (typically 3,000-25,000 V). When you then touch a grounded conductor, the excess electrons discharge in a tiny spark that you feel as a shock. The discharge current is tiny (milliamps for microseconds) and harmless, but the voltage is high enough to ionise a small air gap. Dry air is a poor conductor, so charge accumulates more in winter (low humidity) than in summer. Lightning is essentially the same phenomenon on a vastly larger scale, with clouds accumulating charge through ice-crystal collisions.