While an object in uniform circular motion maintains a constant speed, it's velocity is constantly changing. Here's why:

* Velocity is a vector quantity, meaning it has both magnitude (speed) and direction.

* In uniform circular motion, the object's direction is constantly changing as it moves in a circle.

* Since the direction is changing, the velocity is changing, even if the speed is constant.

Newton's First Law states that an object at rest stays at rest and an object in motion stays in motion at a constant velocity unless acted upon by a net force.

Therefore, a force is absolutely necessary to keep an object in uniform circular motion. This force is called the centripetal force, and it always acts towards the center of the circle.

Think of swinging a ball on a string. You have to constantly pull on the string (providing the centripetal force) to keep the ball moving in a circle. If you let go of the string, the ball will fly off in a straight line, as dictated by Newton's First Law.