·
Centre of Mass: The point at which the entire mass of the
body may be assumed to be concentrated in order to study the motion of the
body under the influence of an external force.
·
Rigid Body: A body is said to be rigid if the distance
between any two particles of the body remains constant, whatever be the
applied force.
·
Moment of Inertia: Moment of inertia is a measure of the
rotational inertia. It is the sum of the products of the masses of the
particles of the body and the squares of
their respective distances from the axis
of rotation. i.e


, where m_{i} is the mass of the

·
i th particle and r_{i} is its
distance from the axis of rotation.
·
Radius of Gyration: It is the distance between the axis
of rotation and the point where the entire mass of the body can be assumed to
be concentrated so as to give the same moment of inertia as that of the body
about the same axis. Radius of gyration,
K =


, where I is the M. I. and M the mass of the body.

·
·
Principle of Parallel Axes: It states that the
M.I. of a body about any axis is equal to the sum of its M.I. about a
parallel axis through its C.M. and the product of its mass and the square of
the distance between the two parallel axes.
·
Principle of Perpendicular Axes: This principle is
applicable to a plane lamina. It sates that the M.I. of a plane lamina about
an axis perpendicular to its plane is equal the sum of its M.I. about two
mutually perpendicular axes in the plane of the lamina and passing through
the point where the perpendicular axes cuts the lamina.
·
Angular Momentum: It is the product of the M.I. of the body
and the angular velocity of the body.
\ Angular momentum L =
Iw, where I is the
M.I. and w is the angular
velocity.
Law of conservation of Angular Momentum: This law states that if the
resultant external torque acting on a body is zero, its angular momentum
remain constant.
