## Sunday, January 10, 2016

### Rotational Motion An Introduction and Comparison

Motion is the change in the position of the body with respect to its initial and given position. If a body is not changing its position with respect to time and position, then the body is said to be in the state of rest. If a body is changing its position with respect to time and position, then it is said to be in the state of motion. Depending on how does the body moves, there are three different kinds of motion.

If all particles of the body are having the same kind of displacement and velocity during the motion, then the body is said to be in translatory motion. We consider the concept of particle to understand this translatory motion. Particle is a body with negligible dimensions like mass and length. All classical mechanics concepts were actually explained in terms of particle.

As any body is a combination of similar particles, the rules that were valid for particle were also valid for body. One dimensional motion, two dimensional motion, dynamics, collisions are some of the topics where we study classical mechanics using this translatory motion.

If different parts of body are having different kinds of motion, to study the translatory motion, we use the concept of center of mass. Center of mass is a point of a body or a system that represents the actual motion of the body.

If the body is rotating about a axis, then it is called rotational motion. The axis around which the body moves is called rotational motion. All particles of body rotates here about its axis of rotation. We need different kinds of physical quantities to study rotational motion when compared with the translatory motion. Moment of inertia and torque are simple example physical quantities using which we study and understand rotational dynamics.

If a body is having to and fro motion about a fixed point, then it is said to be in oscillatory or vibratory motion. The point of reference about which it is oscillating is called mean position or equilibrium position. It is also called harmonic motion and it happens between two fixed points.

Again to study oscillatory motion, we cannot use the concepts developed that are developed in translatory motion and rotatory motion and we need different set of rules like time period and frequency to understand them.In the following video lesson, all this is described in detail.

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