Numbers and MKS Units
The MKS (meter-kilogram-second) units is part of the SI (Systeme
Internationale) that is the standard in much of the world and for scientific
work.
Length
- The meter was originally defined as 1/10^{7} of the distance from
the equator to the North pole measured along a longitude passing through
Paris.
- In 1899 it was defined as the length between two marks on a particular
platinum-iridium rod kept in Paris. Then in 1960 the meter was redefined as
1,650,763.73 wavelengths of a particular orange light emitted by krypton-86.
- Basic numbers:
Radius of nucleus: 10^{-15} m
Radius of atom: 10^{-10} m
Radius of bacteria: 10^{-4} m
Length of your stride: 1 m
Radius of earth: 6 x 10^{6} m
Radius of earth's orbit: 10^{11} m
Distance to nearest star: 10^{16} m
Radius of our galaxy: 10^{21} m
Radius of the universe: 10^{27} m
Mass
- The kilogram was originally defined as the mass of 1 liter of water. One
kilogram is about 2.2 pounds (careful! kilogram is a mass unit, pounds is a
force unit).
- The standard kilogram is a particular platinum-iridium cylinder at the
International Bureau of Weights and Measures near Paris.
- Basic numbers:
Mass of electron: 10^{-30} kg
Mass of Hydrogen atom: 10^{-27} kg
Mass of bacteria: 10^{-15} kg
Mass of one liter of water: 10^{0} kg
Mass of large ship: 10^{8} kg
Mass of earth: 6 x 10^{24} kg
Mass of sun: 10^{30} kg
Mass of galaxy: 10^{41} kg
Mass of universe: 10^{52} kg
Time
- The second is defined as the time required for 9,192,631,770 periods of the radiation emitted from a particular transision of a cesium atom.
- Basic numbers:
Time for electron to orbit an atom: 10^{-18} sec
One year: π x 10^{7} sec
Human lifespan = 2 x 10^{9} sec
Age of the Earth = 10^{17} sec
Age of the universe = 10^{18} sec