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Name: Kim
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Question:
How is bending a stream of water possible, using static electricity?



Replies:
Benjamin Franklin demonstrated that 'charges' can be moved from one surface to another by rubbing - such as rubbing silk on ebony. You can create similar charges by rubbing a rubber balloon on a woollen jumper, or by rubbing a plastic toy on the cat's fur. Benjamin thought that the electric charge was being created - we now know that electrons are being dragged from one surface onto the other. You will always create two charged items together - one positive and one negative.

Once a charge has been made, like charges will repel and unlike charges will attract. The balloon you rub on your jumper will then be attracted to your jumper, and you can carry the balloon around the room just by its attraction. The toy you rub on the cat will cause the cat's fur to rise up and follow the toy (which will annoy the cat immensely by the way). If you bring a charged item close to a thin stream of water, then the water will be attracted to the charged item. While the water is not charged - either the same as the balloon or opposite to it - its charge is different, so it can be attracted.

The easiest way to demonstrate this simple experiment - Start the tap running to produce a thin steady stream of water. Rub a plastic ballpoint pen in your clean hair, and then bring it close to the stream of water - the water will be attracted and the steam will curl underneath your pen without touching it.

(By the way - Benjamin Franklin was the one who chose to name the charges negative and positive - unfortunately he got the labels back to front - because now the flow of electricity and the flow of electrons are opposite - causing great confusion to every student of electronics ever since.)

Nigel Skelton
Tennant Creek High School
AUSTRALIA


Do you want to know if it is possible, or to understand why it happens?

Yes, it is possible. It is easy to do it yourself.

It works because water, like all substances on earth, is made of electric charges. A static electric charge near the water stream will repel the like charges in the water and attract the unlike charges. Since the force of electric interaction is stronger at close distance than at long distance, the unlike charges will be attracted more strongly than the like charges will be repelled. Thus, the net interaction will be for the water stream to be attracted to the charge.

Richard Barrans Jr., Ph.D., M.Ed.
Department of Physics and Astronomy
University of Wyoming



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