CHAPTER 5
: ROTATIONAL MOTION
5.1 Rotational Motion of a rigid body about a fixed axis
A rigid body is defined as a system of particles, the distance between any pair of which remains unaltered.
This is an ideal condition, but objects like a metal block or a log of wood under moderate forces
and torques approach very close to being 'rigid' bodies.
The rotational motion of a rigid body about a fixed axis can be described by introducing concepts
of Moment of Inertia, torque, angular momentum etc.
Consider a rigid body rotating about a fixed axis. Let
m_{i}, be the mass of the i^{th} particle, let
r_{i} be its^^{r } distance from the axis and let
vi be its tangential velocity ^^{r} to radius r_{i} of the circle in which the
particle rotates with same angular velocity as that of the body.
The Quantity I is called the moment of Inertia (M.I) of the rigid
body about the given axis. It is defined as the sum over the body
of mass of each particle multiplied by the square of its ^^{r}
distance from the axis of rotation. Its unit is 1 Kg x m^{2}.
