**Circular Motion**

**Introduction:**

Physics
deals with various types of motions. In daily life we come across various
practical situations involving motion. A cyclist travelling along a straight
road performs rectilinear (linear) motion. A cyclist taking turn along a curved
road, perform a curvilinear motion. A cyclist moving along a circular race
course track perform a circular motion.

The
circular motion is a special case of linear or translator motion, in which
particle revolves along circumference of a circle.

Following
are some examples of a circular motion.

*(1) Motion of earth and other planets around the sun.*

*(2) Motion of an object tied at the end of a string and whirled in a circle.*

*(3) Motion of tip of minute hand, hour hand and second hand of a clock.*

*(4)*

*Motion of roller coaster looping the loop.*

**Angular Displacement:**Angular displacement is defined as the angle described by radius vector in a given time at the centre of circle.

**Angular Velocity:**

**The S.I. unit of angular velocity is rad/s.**

The direction of
angular velocity is given by right hand rule and is in the direction of angular
displacement.

**Angular acceleration:**The angular acceleration is defined as the time rate of change of angular velocity.

**The S.I. unit of angular acceleration is rad/s**

^{2}**When an electric fan is**

*e.g.***, the blades of fan move with increasing angular velocity with time. The angular acceleration in this case will have same direction as the angular velocity. When the electric fan is**

*switched on***, the angular velocity of blades of fan decreases with time. The angular acceleration now will have direction opposite to that of angular velocity.**

*switched off*

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