Question

when is an object said to be in the uniform motion

Answer 1

When an object covers equal distances in equal interval of time then the object said to be in uniform motion.

Answer 2

Accelerating objects are objects which are changing their velocity - either the speed (i.e., magnitude of the velocity vector) or the direction. An object undergoing uniformcircular motion is moving with a constant speed. Nonetheless, it is accelerating due to its change in direction.