The mass of an object is independent of gravity.
The objective of the sphere is to contain 1000x Avogadro's number of atoms (6.022 x 10^26) which will be a constant regardless of where on earth it is located.

 

The mass of an object is independent of gravity.
The objective of the sphere is to contain 1000x Avogadro's number of atoms (6.022 x 10^26) which will be a constant regardless of where on earth it is located.

Agreed but gravitational force is different over the surface of the earth. Things weigh more at the poles then they do at the equator.

It also changes due to local geology (by a minute amount but it still changes) mountains, valleys even the density of the ground under a given location will cause a difference.

But the over all force remains the same for the earth as a whole.

Also every time a probe is shot into space and does not return, the gravitational of the earth would change. By an unmeasurable amount but it would still have to change.

 

The purpose of a standard weight is to be able to compare and calibrate other reference weights to the standard weight. Presumably this will be done at the same geographical location.
Hence it does not matter where on the planet the calibration procedure is conducted.

 

The mass of an object is independent of gravity.
The objective of the sphere is to contain 1000x Avogadro's number of atoms (6.022 x 10^26) which will be a constant regardless of where on earth it is located.

Probably should be 1000/(atomic mass Si) x Avogadro's number of atoms.

 

Just testing to see who's paying attention.

 

I'm paying attention!

A bit surprised that some people don't seem to know the difference between mass and weight, or understand that if you're going to make a million dollar reference, the people that will use it know how to calculate the necessary compensation for location, altitude, relative buoyancy in Earth atmosphere, etc.

 

"Also, cool video. I find the processes in making something more exacting than ever before very intriguing. A lot of clever people."



I remember thinking that, when I first learned to turn a true sphere on a lathe.

When I worked for a major aircraft manufacturer, they needed a nearly perfect sphere for use on one of their coordinate measuring machines for calibration purposes. A sphere was cut on a lathe, two female hemispheres were milled and polished that were just a few thousandths over the size of the lathe cut sphere. A post was inserted into the sphere, the two hemispheres were clamped around it and polishing compound was poured in between. The sphere was turned and wobbled for days with regular changes of the polishing compound. The metrology lab was tasked to make sure the sphere was as near perfect as they could measure, which was quite good with the equipment they had available. The measuring machine was made by Sperry and used drum memory for the operating program and part programs. A 6" long glass rod with a ruby ball on the end was used as a probe. There was an aluminum suitcase with a row of fluorescent indicators across the top and a row of buttons to match used to monitor and alter the program. 1970's tech was quite something to behold.

 

Neat story.

Although I thought it was going to end along the lines of "and then someone sneezed whilst carrying it and dropped it on the floor."