Perfect silicon spheres were developed to redefine the kilogram because the platinum kilogram was changing in weight even in extremely strictly controlled physical conditions. If dust can ruin the platinum kilogram, why are people allowed to touch the silicon version?

Question

How is it that the sphere doesn’t become ‘contaminated’ with extra atoms from skin, clothes or even breath? Or is it just that these contaminants are very easy to clean off afterwards?

In: Physics

Answer 1

It’s important to note that they didn’t want to create just any sphere, they wanted to create the closest thing to a perfect sphere as physically possible. If you can create a perfect(or sufficiently close to perfect) sphere, and the material you make it out of is solid and pure, then using the density of the material, it’s volume, and knowing the molecular mass of the material (in this case silicon) you can get a sufficiently accurate measurement of the number of atoms in that object, and therefore how many moles are in that object and then you can call that object’s mass the kilogram, and then you can define the kilogram in terms of Avogadro’s number.