This image is a perfect example of friction.

Static shocks are as mysterious as they are unpleasant. What we know is this: They occur when an excess of either positive or negative charge builds up on the surface of your body, discharging when you touch something and leaving you neutralized. Alternatively, they can occur when static electricity builds up on something else a doorknob, say which you then touch. In that case, you are the excess charge's exit route.

But why all the buildup? It's unclear. The common (and probably partly correct) explanation says that when two objects rub together, friction the electrones off the atoms in one of the objects, and these then move onto the second, leaving the first object with an excess of positively charged atoms and giving the second an excess of negative electrons. Both objects (your hair and a wool hat, say) will then be statically charged. 

Stephanie Pena