Circulation motion:
In physics, circular motion is a movement of an object along the circumference of a circle or rotation along a circular path. It can be uniform, with constant angular rate of rotation and constant speed, or non-uniform with a changing rate of rotation. The rotation around a fixed axis of a three-dimensional body involves circular motion of its parts. The equations of motion describe the movement of the center of mass of a body.
Examples of circular motion include: an artificial satellite orbiting the Earth at constant height, a stone which is tied to a rope and is being swung in circles, a car turning through a curve in a race track, an electron moving perpendicular to a uniform magnetic field, and a gear turning inside a mechanism.
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Angular displacement:
“The angle traveled by a body during its motion a circular path is called its angular displacement.”
When an object rotates about its axis, the motion cannot simply be analyzed as a particle, since in circular motion it undergoes a changing velocity and acceleration at any time (t). When dealing with the rotation of an object, it becomes simpler to consider the body itself rigid. A body is generally considered rigid when the separations between all the particles remains constant throughout the objects motion. But when an object is moved on a curved or circular path then this change in its position from initial to final state is shown by the angular displacement. This rotational quantity is angled at which a body rotates around the axis.
Example parts of its mass are not flying off. In a realistic sense, all things can be deformable; however this impact is minimal and negligible. Thus the rotation of a rigid body over a fixed axis is referred to as rotational motion.
Consider a particle performing circular motion in anticlockwise sense as shown in the figure. Let, A = initial position of particle at t = 0
B = final position of particle after time t. 
θ = angular displacement in time t.
r = radius of the circle.
s = length of arc AB.
Angular displacement is given by,
Unit: radian
Direction of angular displacement is given by right hand thumb rule or right handed screw rule.
State right hand thumb rule to find the direction of angular displacement.
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