This sphere made with Silicon is the roundest object on earth and this may provide new definition for the Kilogram, sounds crazy. Those who have finished their secondary education in Science may know that: the Kilogram is equal to the mass of Platinum Iridium cylinder kept under some basement in a secret vault in Paris.
But, what the Kilogram has to do with the Roundest object on earth? Let's see:
# First unit for mass was the Grave (from Latin word gravitas meaning "weight") and was defined as the weight of 0.1 m cube of water at 0 degree Celsius
# Then to weigh smaller or lighter things the term "gramme" was coined which was mathematically defined as:
1 Grave = 1000 grammes
# Also, the "gramme" was too small so a new term for the "Grave" was the "Kilogram"
# So, this made the Kilogram the only basic S.I. units out of seven having the word "Kilo" as prefix and in 1799 the definition was changed to the mass of water @ 4 degrees Celsius. @ which the water is densest.
# So, as the time passed people realized that making water the measure of mass is not that precise. A platinum cylinder was made having the same mass of the water definition.
# Again in 1889 the platinum cylinder was replaced by the Cylinder of Platinum Iridium called as the "Le Grande"
# The Kilogram is the only basic S.I. unit which is defined by a physical object
# After all this, still there was a problem with this system. It is that mass of the Platinum Iridium varies widely over time as saw in 1948.
# Here is where the roundest object comes in play. the cost of the material from which it is made is 1 million Euros. It is so expensive because it is made from Silicon and only one isotope of Silicon i.e. Si 28
# But why sphere? Because sphere is the most simple shape. i.e. if you know it's diameter, one can all it's geometrical things like volume, area etc.
# How does this Sphere helps in defining the "Kilogram"?
Here it is once we know the diameter we know it's Volume so,
Volume = 3.14x (diameter)^3
Therefore: Volume / Density of atoms = No. of atoms.
NO. OF ATOMS=2.15 X 10^25
# So, we have redefined the definition of Avogadro, No.
it is defined as the no. of atoms in 12 gms of Carbon 12.
# Even if the Silicon Sphere is damaged we have the official definition of "Kilogram" as
"Mass of 2.15 x 10^25 atoms of Silicon 28"
# Now may the Kilogram will be defined by a concept not by a physical object.
source: Youtube Channel Vertasium