(I) UNIFORM LINEAR MOTION:- When a body is moving with constant velocity then the motion is said to be uniform linear motion. Velocity is a vector quantity because it has both Magnitude and direction .So if we say constant velocity it means that both direction and magnitude are fixed and the body moves in a straight line without a change in its speed.
For example, A train moving with constant speed on a straight track.
(II) UNIFORM CIRCULAR MOTION:- When a body moves at a constant speed in a circle then the motion is said to be uniform circular motion. In this case the magnitude of velocity is fixed but the direction is not fixed and changes at every moment. When a particle moves in a circle then the tangent at every point on the circle gives the direction of velocity at that point.
For example, A kid on a merry go round which is moving with constant speed in a circle.
Final Answer
In uniform linear motion, the speed and direction of motion is fixed and so, it is not accelerated.
Example- A car running on a straight road.
In uniform circular motion,the speed is constant but the direction of motion changes continuously and hence, it is accelerated
Example- Motion of earth around the sun.