# Definition:Linear Measure

## Definition

Linear measure is the means of measurement of physical displacement.

### Symbol

The usual symbol used to denote linear measure is $l$.

### Dimension

Linear measure is one of the fundamental dimensions of physics.

In dimensional analysis it is assigned the symbol $\mathsf L$.

### Units

The units of measurement of linear measure are as follows:

Thus:

$1 \ \mathrm m = 10^2 \ \mathrm {cm} = 100 \ \mathrm {cm}$
$1 \ \mathrm {ft} = 30.48 \ \mathrm {cm} = 0.3048 \ \mathrm m$

### Length

Length is linear measure taken in a particular direction.

Usually, in multi-dimensional figures, the dimension in which the linear measure is greatest is referred to as length.

It is the most widely used term for linear measure, as it is the standard term used when only one dimension is under consideration.

Length is the fundamental notion of Euclidean geometry, never defined but regarded as an intuitive concept at the basis of every geometrical theorem.

Breadth is linear measure in a dimension perpendicular to length.

In the context of a two-dimensional geometric figure, the breadth is in the plane of that figure.

In a three-dimensional figure, the choice of which direction is referred to as breadth is often arbitrary.

### Depth

Depth is linear measure in a dimension perpendicular to both length and breadth.

The choice of depth is often arbitrary, although in two-dimensional diagrams of three-dimensional figures, depth is usually imagined as being the dimension perpendicular to the plane the figure is drawn in.

### Height

Height, like depth, is used as a term for linear measure in a dimension perpendicular to both length and breadth.

However, whereas depth has connotations of down, height is used for distances up from the plane.

### Thickness

Thickness, like breadth, is used as a term for linear measure in a dimension perpendicular to both length and depth.

However, whereas breadth has connotations of across, thickness is used for distances through the solid figure.

### Distance

The distance between two points $A$ and $B$ in space is defined as the length of a straight line that would be drawn from $A$ to $B$.