Introduction to Motion

A body that changes its position with time (always relative to the observer) is called a body in motion.

A body that does not change its position with time with respect to its surroundings is called a body at rest.

An object whose size is negligible compared to its range of motion is called a point mass object or particle.

The motion in which only one coordinate changes with time (e.g., motion of a car on a straight road, motion of a freely falling body) is called one-dimensional motion.

The motion in which two coordinates change with time (e.g., an insect crawling over the floor, motion of a car turning at a corner) is called two-dimensional motion.

The motion in which position changes in space with time with respect to a frame of reference (e.g., motion of a kite) is called three-dimensional motion or motion in space.

The motion in which a particle covers equal displacements in equal intervals of time — requiring no net force — where velocity is independent of choice of origin and time interval is called uniform motion.

The motion in which an object covers unequal distances in equal intervals of time, or when a body travels equal distances in unequal intervals of time, is called non-uniform motion.

The motion in which the velocity of an object changes equally in every equal interval of time — shown by a horizontal line in the acceleration-time graph indicating constant acceleration at any moment — is called uniformly accelerated motion.