Static electricity in winter

What causes the electrical shock I receive when getting out of a car during the winter? —Vicello (age 36)

The shock you get when getting out of your car, particularly in the winter, is from static electricity. Static electricity often occurs whenever two dissimilar materials are rubbed together. When electrons, or the negative charge, are removed from one material and deposited on the other a static charge results. When you are in a car the seat is one material and your clothes are another when you move you create friction and build up a static charge. Once your body accumulates enough of a charge and then touches a good conductor, usually metal like the car door the charge quickly leaves you and you feel the shock.

The reason you feel this shock more in the winter than in the summer is due to the amount of humidity found in the air around you. In the summer the air is very moist and full of water molecules in the winter the air has fewer water molecules or is “dry”. These water molecules act as an electrical conductor — in the summer the high amount of water in the air can easily cause the charge to dissipate but in the winter since there are less water molecules the electrical charge goes through your body instead.

Be aware of this phenomenon when pumping gas into your car. After getting out of your car, always touch something metal first that is far away from any gas fumes. Many people will begin pumping gas and then get back into the car while the gas is pumping. When they get back out of the car and reach for the gas pump, a spark jumps and can ignite the gas fumes.

Good luck future scientist,

Professor Science

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