Think back to the last time a thunderstorm swept through your area. A bolt of lightning streaked across the sky, followed moments later by the crash of thunder. Have you ever wondered what causes lightning? Perhaps you've observed something similar on a smaller scale closer to home. When you take clothes out of a dryer, some of them can stick together, like the socks and towel in Figure 1. If you pull the clothes apart in a darkened room, you can see sparks that are like tiny bolts of lightning. This shouldn't be surprising once you realize that lightning and “static cling” have a similar cause—the movement of electric charges.

Figure 1  Electric charge is responsible for clothes that stick together when they are removed from a dryer.