Encyclopedia of Electrical Engineering
Encyclopedia of Electrical Engineering


In physics we are concerned with three types of motion: translational, rotational, and vibrational. A car moving down a highway is an example of translational motion, the Earth spin on its axis is an example of rotational motion, and the back-and-forth movement of a pendulum is an example of vibrational motion. From everyday experience we recognize that motion represents a continuous change in the position of an object.

Translatory Motion

The motion in which all the particles of a body move through the same distance in the same time is called translatory motion.
Fig. No.1: Both of the motions are Translatory.
In our study of translational motion, we describe the moving object as a particle regardless of its size.
In general, a particle is a point-like mass having extremely small size. For example, if we wish to describe the motion of the Earth around the Sun, we can treat the Earth as a particle and obtain reasonably accurate data about its orbit.
As an example on a much smaller scale, it is possible to explain the pressure exerted by a gas on the walls of a container by treating the gas molecules as particles.
There are two types of translatory motions: Rectilinear motion; Curvilinear motion. Both of the types are defined and visualized in the Fig. no.1. Examples: are motion of car, aeroplane, rocket etc.

Rotational Motion

A rotation is a circular movement of an object around a center (or point) of rotation. Every rigid body has a center of rotation. In the rotation, every point makes a circle around the central point.
Fig. No. 2: Earth rotates around its orbit as it revolves around the sun.
So, there is an equal distance from the centre to any point of the shape. if the the body is placed in rotation by applying external force, the center of rotation is always forcing the body to be rotated around itself. It is due to the rotational motion of earth, which continuously alter days and nights by a rotational (circular) motion around its center of mass. But our earth planet also revolves around the sun which continuously alter seasons around the world.
What is Revolutional Motion?The term revolution is used to describe a motion, wherein an object moves in a circular direction around an object or centre, in a fixed path or orbit. It involves travelling around an axis outside the object, i.e. external axis. The distance travelled by an object, in one revolution, around the circle, is nothing but its circumference. The time taken by an object to complete one revolution around the circle is known as the period, represented by T. The revolution of the Earth around the Sun is in the anticlockwise manner, which takes 365 days and 6 hours to complete. It is the only reason for causing seasons to change.

Vibratory Motion

A body moves to and fro about its mean position periodically is called vibratory motion.
Fig. No.3: The Figure shows vibratory motion
Vibratory motion can be described as any object moving/swinging back and forth, moving up and down, pulsating, spinning, or vibrating. swinging; pendulums, swings, metronomes are the example of vibratory motion.