Rigid Body :
Rigid body is defined as a system of particles in which distance between each pair of particles remains constant (with respect to time) that means the shape and size do not change, during the motion. Eg : Fan, Pen, Table, stone and so on.
Two blocks with a spring attached between them is not a rigid body.
For every pair of particles in a rigid body, there is no velocity of seperation or approach between the particles. In the figure shown velocities of `A` and `B` with respect ground are `V_A` and `V_B` respectively.
If the above body is rigid `V_A cos theta_1 = V_B cos theta_2`
Two blocks with a spring attached between them is not a rigid body.
For every pair of particles in a rigid body, there is no velocity of seperation or approach between the particles. In the figure shown velocities of `A` and `B` with respect ground are `V_A` and `V_B` respectively.
If the above body is rigid `V_A cos theta_1 = V_B cos theta_2`