Describe briefly translatory and rotatory motion of a rigid body.
Translatory Motion: In pure translatory motion, all particles of the rigid body move with the same velocity at every instant of time.
For example when a rectangular block of wood slides down an inclined plane, then, all particles (P1 and P2 move with the same velocity.
Rotational Motion: In rotatory motion of a rigid body about a fixed axis, every particle of the body moves in a circular path lying in a plane perpendicular to the axis and has its centre on the axis.
In the above fig. it has been shown that a rigid body is rotating about z-axis. All the particles of body P1,P2etc.describe circular path of radii r1,r2 etc. The planes of these circles are perpendicular to the axis of rotation with their centers on the axis of rotation. For a particle P3 lying on the axis of rotation r=0, such that during the motion the particle remain stationary.