Le Grand K Gets Fired
Le Grand K is a platinum-iridium alloy cylinder, that’s represented the official definition of a kilogram since 18 89. That changed last week. A kilogram is now defined as the fixed numerical value of the Planck constant h to be 6.626 070 15 × 10-34 when expressed in the unit J s, which is equal to kg m2 s -1 !
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