Kilogram Reference Losing Weight

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Helmut Jilling

Auditor / Consultant
#12
I wonder how they were able to take into account the changing of standard accuracy. Has it been losing weight, or variance in measurement?

Also, I wonder what kind of material it is made of; that may have something to do with it.

At one time, many years ago, they also had a calibrated standard for a liter. They used wine as the liquid, in a corked and sealed bottle, but a thirsty french labman drank it one evening...:notme:
 

Ron Rompen

Trusted Information Resource
#13
Ummmm.....am I the only one who noticed the discrepancy here?

A kilogram is (from my grade 9 science class) a unit of MASS, not a unit of WEIGHT.

If the standard is losing 'weight', then perhaps it's not the standard that is at fault at all, but rather GRAVITY....oh my god, my 8 yr old was right when she said that one day it would stop and we would all fly off!!!!!!!!
 
M

M Greenaway

#14
Hey thats a great theory, and gravity definately isnt a constant because it depends on the distance between the two bodies, so if I hold my standard of mass a little higher the gravitational forces will be less, and therefore it will appear to weigh less !

This is pure speculation and I am in way over my head on this one !

Alternatively of course it could be that the earth itself is losing mass - global warming, ice caps melting, life on mars - it all makes sense now ha ha ha ha !!!!!!!!!!!!!!!!................

er more coffee please
 

Hershal

Metrologist-Auditor
Staff member
Super Moderator
#15
Hey thats a great theory, and gravity definately isnt a constant because it depends on the distance between the two bodies, so if I hold my standard of mass a little higher the gravitational forces will be less, and therefore it will appear to weigh less !

This is pure speculation and I am in way over my head on this one !
Actually you are right on track.....if you calibrate an analytical balance for example, it must be calibrated in situ, as the barometric pressure and local acceleration of gravity do in fact change, depending on a number of variable - to include altitude (or distance from Earth's core if you prefer).
 

Kales Veggie

People: The Vital Few
#16
Can anyone shed some light on what the ideas are to replace the 1 kg mass with ?

----------------
for interested parties -- the international units are:

length -- meter m
mass -- kilogram kg
time -- second s
electric -- current ampere A
thermodynamic -- temperature kelvin K
amount of substance -- mole mol
luminous intensity -- candela cd

All other units are derived from these 6. Amazing, right?
-------------
 
M

Mr Niceguy

#17
Can anyone shed some light on what the ideas are to replace the 1 kg mass with ?
One of the prime candidates for the kg standard is another artefact, but only temporarily. Basically the mass standard would be defined as a specified number of silicon atoms. Silicon has been chosen since it is possible to prepare at ultrahigh purity in a regular crystal structure. The next step is to prepare a "perfect" silicon sphere, measure its diameter and count the atoms by x-ray crystallography. I think trial spheres are being polished now, but not sure where. Once done to the required uncertainty then for chemists Avogadros number 6.023 x 10E23 would be defined as an exact number. What I am not sure of is how metrologists, physicists etc. will ensure traceability to this number without an artefact.

Concern over the relative weight loss of the prototype kg is nothing new. The BIPM in Paris reported in 1992 on the comparisons over the previous 100 years.
 

Kales Veggie

People: The Vital Few
#18
Thank you for that explanation. Do you know the size and/or weight of the sphere ?

Counting atoms is an interesting task, especially counting to 10^23 or higher.

Avogadro's number is the basis for one of the SI units, amount of substance.
 
M

Mr Niceguy

#19
I don't know the size off-hand. It must be practical to make, test and measure so I guess smaller than a fist.

The point is that at present Avogadro's number defines the mole (amount of substance) no better than the prototype kg, but most chemists don't worry about 1 part in 10E8 uncertainty.

If the spheres are accepted (big if) then the atom count will actually be pretty trivial arithmetic. The diameter will of course be measured in terms in wavelengths of light. The crystal structure will be regularly spaced and the spacing can be determined with very high accuracy. The count will depend only on dimensions of electromagnetic radiation.

Of course there will be much discussion about how many atoms of silicon = mass of 1 kg , but once defined that's it.
 
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