In this IIT JEE physics video, we are going to discuss the rotational motion. The topics covered in the above physics video are,

  • Rigid body and its rotation
  • Axis of rotation
  • Some exemplary problems
  • Moment of inertia

So what is a rigid body? Ideally, a rigid body has a definite size and shape. No pair of particles of the rigid body can have relative motion. A rigid body can have,

  1. Pure translator motion: The object moves only in one direction. In the case of the rigid body, all the particles will have same velocity vector.
  2. Pure rotational motion: The rotation is about a fixed axis.
  3. Both the motion simultaneously.

Further, we have discussed axis of rotation. In the above jee physics video, we have explained this topic with the help of a diagram. This will help you understand the topic well. If there are three particles, then their planes are perpendicular to the axis of rotation. So how do we define axis o rotation? Its definition is, “every and each point or particle of the body moves in a complete or part of a circle, This circle lies in a plane perpendicular to the considered axis of rotation and has this as its center on the axis.” This is applicable for both variable and stable axis of rotation.

Then we have discussed very simple and small exemplary problems which will help you understand the topic well.

For doing the analysis of rotational motion, we need to understand the axis of rotation is very important. Here we have taken an example of a fixed case and an example of free in space case. In the case of free in space, the axis of rotation passes through the center of mass.  Further, we have discussed angular speed using few exemplary problems.

Then in this iit physics video we have discussed moment of inertia. We already know that mass is the measure of inertia. Moment of inertia is also known as rotational inertia. We have taken two examples of a door and a window and understood that higher is the moment of inertia higher is rotational motion. The moment of inertial of a single particle is,

I =  mr2

Moment of inertia depends on two things,

  1. Mass of the object
  2. The distance between axis of rotation and the object

So this is all about rotational motion. This is a pretty simple topic, if learnt in a proper manner. So make sure that you as an IIT jee physics aspirant master this topic well, as this can fetch you marks not only in this chapter but also in the preceding chapters.