1.MOMENT OF INERTIA
(a)    CALCULATION OF MOMENT OF INERTIA BY DIGITS:
         
      M.I about an axis of symmetry is     [M] mass  *   the sum of squares of                                                                                          perpendicular semi axis
                                                            ______________________________
                                                                              N
where N = 3 --- for rectangular body
                4 --- for elliptical (including circular)
                5 --- for ellipsoidal (including spherical)
ex- for ellipse
      I_z  = M/4  ( a² + b² )

(b) The sum of moment of masses about its centre of mass is always  zero.

(c)  Rolling motion  on an inclined plane :
         velocity        v = [2gs] / [  1+K² / R²  ].
        acceleration  a = gsin / [ 1 + K² / R² ].
         Where, s = distance of inclined plane
                     K = radius of gyration
                     R =  radius of symmetrical body
(d) Angular velocity of a point whose motion  is in a plane:
     r²d/dt = 2v * p
     where p = perpendicular from the point O upon the tangent at P to the path          of the moving particle.     
                       
(e) The large moment of inertia helps keeping the motion uniform.
 
(f) If a number of torques acted on  a system and the system is in rotational            equilibrium, then  clockwise torque = anticlockwise torque.


2.ROLLING MOTION ON A  INCLINED PLANE
      mgh = 1/2mv² [1 + I/mr² ]
              t = 1/sin 2h [ 1 + I / mr² ] / g

I = moment of inertia
  therefore two bodies of the same shape but of different  masses and radii reach the bottom at the same time.