Rotational dynamics deal with the rotation of a rigid body about an axis of a rotation. Here we study the motion of the rigid body that rotates about an axis. Some examples of rotational motion are the wheels of a bus rotating about an axle, opening, and closing of the door about an axis, etc.
We define rotational motion for solid objects as they are considered as rigid bodies because the particles of solid are arranged in their positions application of an external agent can not change their positions. However, we should remember that nothing can be considered 100% rigid.
A rigid body is said to be rotational motion if all the particles of that body rotate about an axis with the same angular velocity ‘
‘ but with different linear velocities ‘
‘.
In the figure, the dots in a rigid body represent some of the particles, which are rotating with the rigid body as they are fixed in that place.
These particles have the same angular velocity ‘‘ but different linear velocities ‘‘ as they all are at different distances from the axis of rotation. Also, the relation 
makes the linear velocity dependent on distance.
In rotational dynamics, the variables that are used to represent and define a motion are changed and replaced with other variables. For e.g. we call velocity ‘‘ for linear motion whereas we have an angular velocity with a symbol ‘‘ for rotational motion, mass in linear motion is changed by the moment of inertia in rotational motion.
Rotational motion is not similar to circular motion. In circular motion we consider a particle rotating around a center with uniform angular velocity whereas, in rotational motion, we consider a rigid body made up of many particles exhibiting circular motion in itself.
Some FAQs about rotational motion
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