This winter has been shocking, quite literally. If you have touched a metal door knob or opened a car door it may have given you an electric shock. Dry air is to blame.
Cold weather is often dry and this winter has been noticeably lacking in humidity, with the exception of some wet and snowy spells. Dry air is poor at conducting electricity, resulting in static electrical charges building up on people. When an earthed metal object is touched those surplus charges are released, triggering a painful shock.
Central heating is also to blame because it creates dry air. Walking across a carpeted floor is enough to release surplus electrons. Those charges can build up on people until the excess electrons jump from someone’s hand on to a metal knob or pipe, giving a shock.
One way to avoid shocks indoors is to use an air humidifier to increase moisture in a room. Putting moisturiser on the skin helps, as does avoiding wearing synthetic clothes. Crackles and sparks of static electricity created when clothes made of man-made fibres are removed can be impressive. Adding fabric softener prevents clothes from clinging to each other with static as they are taken out of a tumble dryer. The softener balances out the negative charges generated as the clothes rub against each other in the dryer.
Static electricity does have its uses. Photocopiers use the electrical attraction to stick charged toner particles on to paper. Electrically powered air fresheners clean the air in rooms by discharging static electricity on to dust particles, smoke particles and pollen and sticking them on to charged plates inside the device.
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Probably the most spectacular demonstration of static electricity is lightning. Particles of ice rushing around in a thundercloud rub against each other, building up charges that separate into positive at the top of the cloud and negative at the bottom. Eventually the negative charges jump to Earth as a giant spark — what we see as lightning.