Why is density a derived unit?

1 Answer
Mar 1, 2017

Density is a derived unit because it is defined in terms of other units.


Density is measured in #kg*m^-2#. This means that it is derived from fundamental units which are the kilogram and metre.

The kilogram is defined as the mass of a platinum-iridium cylinder which is kept in France. This is the only fundamental unit which is still defined by an artefact.

The second is defined at the time take for #9,192,631,770# transitions of a caesium 133 atom. The speed of light is defined to be exactly #299,792,458 ms^-1#. Now the metre is defined to be the distance light travels in #1/(299,792,458)# seconds.

hence the kilogram and the metre are SI units and density is a derived unit from these units.