# International System of Units (SI) - base units

International System of Units (SI)

This system, contenting 7 base units, should be used in all country's all over this world (I don't know what's with other planets and dimensions ;-) ), but as we all know : IT IS NOT!

It is also called metric system. All units (except time) base on 10 and you can write ANY other unit of the SI with using a combination of the 7 base units. This make it quite useful if you have to do a lot of calculation with a lot of different units. When you write all units in your equviations in the base units it's very easy to calculate wich unit you get with the result.

This system is mostly used in science, but if you go to the field of engineering it's horrible because there are other systems in use. Life could be so easy :-)

Following is a list of the 7 base units and there description. As they started the system (in the 19 century) they created some standard by just saying: „Well, I think this piece of wood looks very good. Let's call it ... erm ... meter.“ But nowadays they try to find more reliebale standard values for this units. That's why some description look very strange.

#### Meter - unit of length

1 m (Meter) = length of the way travelled by light in vacuum during a time of 1/299 792 458 of a second

#### Kilogramm - unit of mass

1 kg (Kilogramm) = mass of the international prototype of kilogramm (which is situated in Paris and they haven't found any other description yet)

#### Second - unit of time

1 s (Second) = time of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom

#### Ampere - unit of electric current

1 A (Ampere) = constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 x 10-7 N1 per meter of length

#### Kelvin - unit of thermodynamic temperature

1 K (Kelvin) = thermodynamic temperature, fraction 1/273.16 of the thermodynamic temperature of the triple point of water2

#### Mole - unit of the amount of substance

1 mol (Mole) = amount of substance of a system, which contains as many specified elemantary entities (atoms, ions, molecules etc.) as there are atoms in 0.012 kilogram Carbon 12

#### Candela - unit of luminous intensity

1 can (Candela) =luminous intensity of a source, when it emits monochromatic radiation of 540*1012 Hz3 and with a radiant intensity of 1/683 W4 per steradian5 in a given direction.

1 1 N (Newton) = kg*m*s-22 (triple point = solid, liquid and gaseous state of a substance exist together)3 1 Hz (Hertz) = 1/s 4 1 W (Watt) = kg*m2*s-35 unit of angle in 3D-Space
1 1 N (Newton) = kg*m*s-22 (triple point = solid, liquid and gaseous state of a substance exist together)3 1 Hz (Hertz) = 1/s 4 1 W (Watt) = kg*m2*s-35 unit of angle in 3D-Space