## Pradeep Kshetrapal is teaching live on Unacademy Plus

PHYSICS for NEET and JEE Pradeep Kshetrapal Class XI Portion

Chapter 4- Motion in a Plane Circular motion Introduction Phy-XI-4-10

CIRCULAR MOTION: A point P is moving in a path around a point O such the distance between the points remains the same. This motion is called circular motion and the path is formed by it is called a circle

In this circular motion the value of x and y co-ordinate changes continuously. Linear displacement Length In linear motion with time, displacement changes and is being calculated as d or s. 50 300 Angular displacement angle Like wise, in circular motion the angular displacement change:s and is calculated as .

There are two types of displacement covered in circular motion. (i) Linear displacement. (ii) Angular displacement. Linear displacement Length 50 0 300 Angular displacement angle

For a very small angle d9 approximately equals to zero the arc and the linear displacement is approximately same. So, for convenience of calculation we take the arc made by the angle and linear displacement equal and let us suppose it is equal to dx. dx

We know that do- Arc Radius dx dx de This shows the relation between linear displacement and angular displacement.

Axis of rotation is a line perpendicular to the plain of rotation of the point, and passes through the centre of the circle. disc axis

Angular displacement is a vector quantity it has direction and is given by axis. All circular quantities like displacement, velocity, acceleration and force are vector quantities, their direction is along the axis and is given by right hand curl rule.

Right hand curl rule states that "If we curl the fingers of our right hand and hold the axis of rotation with fingers pointing in the direction of motion the n the outstretched thumb gives the direction of the angular velocity"

When the rotation is clockwise, the axis is going inside the plain and is known as negative rotation.

Angular displacement e Average angular velocity- time taken For one rotation if time taken is T and angle made is 2 then angular velocity is . Its unit is radian s Instantaneous angular velocity- When the point completes one rotation and again comes to its initial position it is known as one cycle 2 dt

ANGULAR FREQUENCY: Angle made in one second is known as angular frequency. One cycle angle made is 2 and time taken is T therefore angular frequency is That shows Angular velocity-Angular frequency. Unit of angular frequency is radian s 2 for earth. 2 rad s-1 24 60 60

Relation between Angular velocity and linear velocity. dxV dx dtRdR(linear velocity).

change in angular velocity time taken Angular acceleration - dw