Sometimes when we touch some metals,we get a slight shock the reason of this shock is static electricity.
When you move, you generate a static charge by an effect called triboelectric effect.
Two objects come into contact, one has a greater affinity for electrons than the other, so that one comes away with more electrons. This has a greater effect on nonconductors, as the charge tends to stay put, then. But one can be a conductor like your body, plus charge can transfer from nonconductive clothing or shoes to your body.
Friction is not necessary, but it is an effective way of making and breaking contact between surfaces very quickly. Thanks for the animations from Electro Static Technology, Inc.
Electric charge and distance raise the voltage. So you walk around the house, your shoes touching the floor, your clothes rubbing each other and your body, maybe you pet your cat or run a comb through your hair. Then you touch something metal that is grounded, and you discharge in a very high but short current pulse, high enough current so you can feel it and hear the snap.
But humidity in the air tends to make the surfaces of conductors leaky insulators, so charge will drain off. It takes at least 5kV before you will even notice the spark. Cold air can’t hold as much moisture as warm air. So your furnace or heater is warming air that was cold, so you end up with very dry warm air. This allows much higher voltages of static charge to build up on you and other things.
Artificial fabrics (rayon, polyester, etc.) are excellent insulators and so are the worst offenders. Natural fibers tend to be a bit hygroscopic (moisture friendly) and so aren’t as bad at generating static charge. Dryer sheets and fabric softener prevents static cling by leaving your clothes a little electrically conductive.
It is very common these days for manufacturers to add substances to plastic items to make them slightly conductive, to limit the buildup of static charge. Combs and brushes, for instance. When I was a boy, I had to get my comb a little wet before using it, or my hair would stick up like I’d been holding a Van de Graaf generator.