Why is density a derived unit?

1 Answer
Phillip E.
Mar 1, 2017

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

Explanation:

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.

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