Imagine a disc rotating about the axis passing through its centre. Also assume that the disc is made up of many particles. You can observe that the particles at the edge are moving very fast. But the particles near the axis are moving very slow. In fact, the linear velocity gradually increases, as we move from axis to the edge along the radius. This fact should be taken into account when we make rotating devices like DVD player, wheels, gears etc., When a whole body moves in a straight line, all the particles in the body moves with the very same velocity.