Question

in uniform circular motion, is the linear and angular velocity constant? what about the accelerations ? is velocity considered as changed if the magnitude remains constant but direction changes?

Answer 1

The anglular velocity is constant but the linear velocity changes, this is because the direction of the linear velocity keeps on changing.
Because the motion is uniform, the angular velocity is constant hence the angular acceleration is zero, and also the linear acceleration is zero, but due to the change in the direction of the linear velocity, there is another acceleration that is acting inward which is called as the centripetal acceleration.
Yes velocity is considered as changed if the magnitude remains constant while the direction changes, because it is a vector quantity. It is defined by both direction and magnitude.