Linear motion, also known as rectilinear motion, is motion in one spatial dimension along a straight line. It can be described mathematically using only one spatial dimension. Linear motion can be of two types: uniform linear motion, with constant velocity (zero acceleration); and non-uniform linear motion, with variable velocity (non-zero acceleration) . An example of linear motion is an athlete running a 100-meter dash along a straight track. According to Newtons first law of motion, objects that do not experience any net force will continue to move in a straight line with a constant velocity until they are subjected to a net force. Under everyday circumstances, external forces such as gravity and friction can cause an object to change the direction of its motion, so that its motion cannot be described as linear. Linear motion is the most basic of all motion.

In general motion, a particles position and velocity are described by vectors, which have a magnitude and direction. In linear motion, the directions of all the vectors describing the system are equal and constant, which means the objects move along the same axis and do not change direction. The analysis of such systems may therefore be simplified by neglecting the direction components of the vectors involved and dealing only with the magnitude.

Linear motion is used to describe the motion of an object whose velocity vector does not continuously change direction/06%3A_Applying_Newtons_Laws/6.02%3A_Linear_motion). An object moving around a circle, with its velocity vector continuously changing direction, would not be considered to be undergoing linear motion/06%3A_Applying_Newtons_Laws/6.02%3A_Linear_motion). When an object undergoes linear motion, we always model the motion of the object over straight segments separately/06%3A_Applying_Newtons_Laws/6.02%3A_Linear_motion). Over one such segment, the acceleration vector will be co-linear with the displacement vector of the object (parallel or anti-parallel) /06%3A_Applying_Newtons_Laws/6.02%3A_Linear_motion).

Examples of linear motion include the motion of a car on a straight road, freefall of objects, and bowling. Linear motion is a change in position from one point to another in a straight line in one dimension. Displacement is a vector quantity, and it is the distance travelled...