The 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).
The motion of a particle (a point-like object) along a line can be described by its position
An example of linear motion is an athlete running a 100-meter dash along a straight track.
According to Newton's 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.
In general motion, a particle's 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.
Since linear motion is a motion in a single dimension, the distance traveled by an object in particular direction is the same as displacement.
Overall displacement when he returns home is zero, since the person ends up back where he started, but the distance travelled is clearly not zero.
Velocity refers to a displacement in one direction with respect to an interval of time.
[7] Velocity is a vector quantity, representing a direction and a magnitude of movement.
The magnitude of a velocity is called speed.
[6] The average velocity of a moving body is its total displacement divided by the total time needed to travel from the initial point to the final point.
It is an estimated velocity for a distance to travel.
In contrast to an average velocity, referring to the overall motion in a finite time interval, the instantaneous velocity of an object describes the state of motion at a specific point in time.
It is defined by letting the length of the time interval
The instantaneous velocity shows the position function with respect to time.
Acceleration is defined as the rate of change of velocity with respect to time.
Acceleration is the second derivative of displacement i.e. acceleration can be found by differentiating position with respect to time twice or differentiating velocity with respect to time once.
is the change in velocity over the time interval
The rate of change of acceleration, the third derivative of displacement is known as jerk.
The rate of change of jerk, the fourth derivative of displacement is known as jounce.
In case of constant acceleration, the four physical quantities acceleration, velocity, time and displacement can be related by using the equations of motion.
The gradient of a line on a displacement time graph represents the velocity.
The gradient of the velocity time graph gives the acceleration while the area under the velocity time graph gives the displacement.
The area under a graph of acceleration versus time is equal to the change in velocity.
The following table refers to rotation of a rigid body about a fixed axis:
The component of the force parallel to the motion, or equivalently, perpendicular to the line connecting the point of application to the axis is
The following table shows the analogy in derived SI units: Media related to Linear movement at Wikimedia Commons