The position of a particle refers to its location in the space at a certain moment of time. In general the position is measured by a vector joining a fixed point (known as origin) to the moving particle. This vector is known as Position vector.

x(t) is used to represent position as a function of time.

In two dimensions, either cartesian or polar coordinates may be used, and the use of unit vectors is common. A position vector r may be expressed in terms of the unit vectors.

In three dimensions, cartesian or spherical polar coordinates are used, as well as other coordinate systems for specific geometries.