Queasy quandary
Maggie McDonald, of Waikouaiti, asked:
A friend of mine has a piece of rubber attached to the rear of her car which is in contact with the road when she drives. When I asked her about it, she said it stops car sickness. Is this a fact or a myth? If fact, how does it work?
John Campbell, a physicist at the University of Canterbury, responded:
A few decades ago it was a common belief that having a car earthed through an electrical conductor was beneficial. The device needed to be not rigid, so a steel chain or a conducting strip of rubber with fine wires embedded in it was normally used. The devices were used to reduce the buildup of static electricity on the vehicle, but some people reported that they suffered less travel sickness when using the discharge strips, so they were also sold as an antitravelsickness aid.
A car is electrically insulated from the road by its nonelectricityconducting tyres. In moving through air, it becomes electrically charged and it used to be quite common on dry days to receive an electrical shock when leaving a car. Or you could receive an electrical shock from steel shelving in libraries. Slightly conducting fabrics are now frequently used in car seats and carpets, reducing the occurrence of these shocks.
If you have any object moving through a nonelectricityconducting fluid it can build up an electrical charge. The potential difference can build up until a discharge (e.g. a spark or lightning bolt) passes between them. This was a big problem in steel grainsilos and some, when being filled, exploded, with fatal consequences. In pouring grain into a silo, the grain dust (an explosive) could be made to combine with the oxygen in air by electrical discharge, a spark. The trick is to ensure the metal silo and filler are connected to the earth by a wire, so the charge cannot build up.
You will see the same when a petrol tanker is refilling a service station’s main tanks. The first thing the driver will do is to connect an earthing wire between his tank and the service station’s steel tanks.
It was also a significant problem when minesweeping ships were made of fibreglass, to avoid the magnetic steel of conventional ships. On being refuelled, the charge buildup could cause the fuel to explode, unless an earthing wire was present.
I don’t know how a buildup of electrical charge could affect the body.
Motion sickness, like seasickness, is caused by the motion detectors in our inner ears.
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