The kilogram is losing weight!

March 1st, 2008 - 5:16 pm ICT by admin  


New York, March 1 (IANS) The kilogram is losing weight and many international scientists believe it is time to redefine it! The kilogram is based on the International Prototype Kilogram (IPK) - or the “Le Grand K” - a bar of platinum-iridium alloy made in the 1880s and kept in a vault near Paris.

Of the seven units of measurement in the International System, the kilogram is the only base still defined by a physical object.

And copies of the IPK have changed over time by either gaining or losing weight as compared to the standard kilogram.

“The idea is to replace the single master kilogram with something based on physical constants, rather than an artefact that could be damaged accidentally,” said Hy Tran of Sandia National Laboratory.

“In the long term, the redefinition (will be) beneficial because of risk reduction and it may enable better measurements in the future,” he added.

Of course, the kilogram will remain the kilogram. It’s only the way it will be defined that will change.

“If and when the redefinition takes place, it will be done in such a fashion as to have minimal or no practical impact with other measured quantities,” Tran said.

“In other words, if it is redefined so as to ensure better than 10 parts per billion agreement, rather than 20 parts per billion agreement, then we will see no major changes immediately,” he added.

At present, the formal definition of the kilogram allows an uncertainty (95 percent confidence) of 40 parts per billion.

The target originally proposed by the International Bureau of Weights and Measures was an alternative definition, such as the experimental measurement of force on the watt balance (or counting atoms on the silicon sphere).

This envisaged deriving the kilogram, matched to experimental measurements of the prototype kilogram, to within 20 parts per billion.

“The watt balance method of defining the kilogram makes the most sense for those of us in electrical metrology and so far it is the most accurate,” said physicist Harold Parks.

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