Definition:Density (Physics)
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Definition
Density is a physical quantity.
The density of a body is its mass per unit volume.
For a homogeneous body it is found by finding its total mass and dividing it by its total volume:
- $\rho = \dfrac m V$
where:
However, if the substance of the body varies throughout, then its density may be a function of position within the body.
Symbol
The usual symbol used to denote density of a body is $\rho$ (Greek letter rho).
Some sources use $d$, but that has so many other uses that it may become confused with other things.
Dimension
The dimension of density is $\mathsf {M L}^{-3}$: mass per unit volume.
Units
- The SI units of density are $\mathrm {kg} \, \mathrm m^{-3}$ (kilograms per cubic metre).
- The CGS units of density are $\mathrm g \, \mathrm{cm}^{-3}$ or, less formally: $\mathrm g / \mathrm {cc}$ (grams per cubic centimetre).
Thus:
- $1 \, \mathrm g \, \mathrm {cm}^{-3} = 1000 \, \mathrm {kg} \, \mathrm m^{-3}$
Area Density
The area density of a two-dimensional body is its mass per unit area.
Linear Density
The linear density of a one-dimensional body is its mass per unit length.
Also see
Sources
- 1921: C.E. Weatherburn: Elementary Vector Analysis ... (previous) ... (next): Chapter $\text I$. Addition and Subtraction of Vectors. Centroids: Definitions: $1$. Scalar and vector quantities
- 1951: B. Hague: An Introduction to Vector Analysis (5th ed.) ... (previous) ... (next): Chapter $\text I$: Definitions. Elements of Vector Algebra: $1$. Scalar and Vector Quantities
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- 2014: Christopher Clapham and James Nicholson: The Concise Oxford Dictionary of Mathematics (5th ed.) ... (previous) ... (next): Entry: density