MadSci Network: Physics

Subject: What will happen if the SI prototype kilogram is lost?

Date: Sat Sep 9 05:22:41 2000
Posted by Tony Le
Grade level: nonaligned School: No school entered.
City: San Jose State/Province: CA Country: USA
Area of science: Physics
ID: 968491361.Ph

I have read that a kilogram is defined as the mass of a certain piece of metal (known as the prototype kilogram) kept in France. The kilogram was originally standardized as the mass of one cubic decimeter (supposedly one liter) of water (at 3.98 C), and the prototype kilogram was created from that. Unfortunately, these standards were first defined long ago when technology couldn't measure quantities to 483 decimal places. The prototype kilogram was found to have slightly more mass than one cubic decimeter of water. The water standard was thrown out in favor of the prototype, and as a result the liter is now defined in terms of the kilogram (instead of the other way around, as originally) - it is that volume of water at 3.98 C which has a mass of one kilogram. (The liter, then, is actually a sliver larger than one cubic decimeter.)

So, my question is: If that block of metal we know as the standard kilogram is lost, or heaven forbid it's scratched or mutilated (or *gasp* dust settles on it - no physicist would ever stand for an error of .000000000001%!), does the SI has a contingency plan to recreate the standard kilogram exactly? Is the plan simply to replicate it from the copies of the standard kilogram floating around?

Re: What will happen if the SI prototype kilogram is lost?

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