Question

Is it necessary that acceleration which causes change in direction only, has a value (Uniform circular motion)? how? does it mean that an object executing uniform motion is really not executing one, because, its magnitude is changing due to the change in direction ?but how? how can we differentiate between acceleration, with a change in direction and magnitude both ?

Answer 1

Yes, it has a value. It is a centripetal acceleration.
A moving body that travels equal distances in equal time intervals (i.e. moves with constant speed) is said to be in a state of uniform motion. A body moving in a circular with a constant speed or a constant angular velocity is said to be in a uniform circular motion. The uniform circular motion is called uniform because speed is constant here.
As we know, a force called centripetal force is always required to keep a body in a circular path. This force results in an acceleration called centripetal acceleration. Centripetal acceleration is directed along the radius and towards the center of the circular path and the direction of velocity is changing continuously (due to the change in direction) in uniform circular motion that's why it is called accelerated motion.
Acceleration is defined as the rate of change of velocity. Velocity involves both magnitude (speed) and direction. If either of them is changed, the velocity will be changed.​