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The standard for the unit of mass, the kilogram, is a cylinder of platinum-iridium alloy kept by the International Bureau of Weights and Measures in Paris. A duplicate in the custody of the National Bureau of Standards serves as the mass standard for the United States. This is the only base unit defined by an artifact. The SI unit of force is the newton (N). One newton is the force which, when applied to a 1 kilogram mass, will give the kilogram mass an acceleration of 1 (meter per second) per second, i.e.

(3.1)

The SI unit for pressure is pascal (Pa). One pascal equals 1 N/m². The SI unit for work and energy of any kind is the joule (J). One joule is equal to 1 N-m. The SI unit for power of any king is the watt (W). One watt is equal to 1 J/s.