# Kinematics

Motion in 1-D/ Motion in a straight line

Mechanics is a branch of physics which deals with the study of motion of a particle. Motion is change in position of the object with respect to time. Different kinds of motion are translational, vibrational and rotational. In translational motion, a particle moves from one point to another point along a straight line. In rotational motion particles of the body describes concentric circles about axis of rotation. In vibrational motion particle performs to and fro motion about mean position. In this chapter we shall confine ourselves to the study of motion of objects along a straight line, also called as rectilinear motion.

Motion: If an object changes its position w.r.t. its surroundings with time, then it is called in motion.

Rest: If an object does not changes its position w.r.t. its surrounding with time, then it is called at rest.

[Note: Rest and motion are relative states. It means an object which is at rest in one frame of reference can be in motion in another frame of reference at the same time.]

Point Mass Object: An object can be considered as a point mass object, if the distance travelled by it in motion is very large in comparison to its dimensions.

Types of Motion:

(1) One Dimensional Motion: If only one out of the three coordinates specifying the position of the object changes with respect to time, then the motion is called 1-D motion e.g. motion of a train along a straight line, an object falling under gravity etc.

(2) Two Dimensional Motion: If only two out of three coordinates specifying the position of the object changes with respect to time, then the motion is called 2-D motion e.g. A circular motion.

(3) Three Dimensional Motion: If all the three coordinates specifying the position of the object changes with respect to time, then the motion is called 3-D motion e.g. a flying bird, a flying aero- plane, random motion of gas molecules etc.