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Okay, get your earplugs ready, Collected Wisdom is about to get the lawn mower out. The clover and weeds need cutting.
THE QUESTION: "Why are some electric motors noisy while others just hum?" asks Ron McKeown of Shefford, Que. Electric lawn mowers and power tools can be noisy while motors in washing machines, which are larger, are quiet.
THE ANSWER: "Many things contribute to noise in a motor, but one rule of thumb is, the bigger the electrical machine, the more efficient it is," writes Andre Brandao, an electrical engineer in Ottawa.
Electrical motors have iron cores, he says. "The iron core is used to facilitate the flow of the magnetic flux that exists inside the electric motor. The volume of the core is proportional to the efficiency of the motor. As the efficiency increases, the machine vibrates less.
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Other factors that contribute to noise, he says, are the machine type and whether it uses brushes or is brushless. "Brushes are mechanical contacts that may become noisy with time. Brushless machines don't have that and therefore are prone to be quieter."
THE QUESTION: Are there agreements among nations regarding the delivery of each other's mail? asked Nancy Thompson of North Bay, Ont. For example, if more letters are mailed annually from a small country to a large country than the reverse, does the small country have to pay a fee to the larger to cover the difference?
THE ANSWER: "Such agreements do exist," writes Daryl Collard of Victoria. He says the Universal Postal Union provides a forum "where the senior postal officials of practically every country and territory in the world meet to agree on rules governing international mail."
He says those rules make up the Universal Postal Convention, which establishes the payments that every national post office must make to other national post offices for delivering the letters and parcels it originates, or transshipping those letters or parcels for delivery in a third country (as in the case of a parcel sent by surface mail from Canada to Mexico, which must be handled by the U.S. Postal Service en route).
The UPU was established in 1874 and became a specialized agency of the United Nations in 1948. It now has 191 member countries.
HELP WANTED
Jesus and his disciples were Jews. Their names were either Hebrew or Aramaic, they were not Jesus, James, Peter etc., writes Ted Fletcher of Toronto. What were those 13 names?
"With tens of thousands of bees in a hive, I assume that disagreement arises," writes Greg Clark of Calgary. "Do bees ever sting each other?"
Tom Landre of Mississauga wonders why so many people back their cars into parking spots in parking lots. "More than a few times I have been walking through a parking lot and been startled by a vehicle that had backed in and was suddenly moving forward toward me. If they had pulled in forward then I, as a pedestrian, would have two signals for their departure. First the brake lights would come on and then the reversing lights." Also, if you are at a shopping centre, would it not make more sense to pull in forward and leave yourself access to the trunk?
Send answers (and questions) to wisdom@globeandmail.com. Include your name, location and a daytime phone number.
