As they same magnitude and opposite direction so they can balance each other

Explanation:
In order to understand why the unbalanced force due to revolving mass is constant in magnitude but varies in direction, we need to first understand the concept of unbalanced forces and rotational motion.

Unbalanced Forces:
Unbalanced forces refer to forces that do not cancel each other out and result in a net force. When an object is in rotational motion, there are usually multiple forces acting on it due to the distribution of its mass. These forces can be divided into two categories: balanced and unbalanced forces.

Rotational Motion:
Rotational motion occurs when an object spins around a fixed axis. In rotational motion, the object's mass is distributed at different distances from the axis of rotation, resulting in a moment of inertia. When an unbalanced force acts on an object in rotational motion, it causes a torque that changes the object's rotational speed.

Constant Magnitude:
The unbalanced force due to revolving mass is constant in magnitude because the mass distribution remains the same. As long as the mass distribution remains constant, the magnitude of the unbalanced force remains constant.

Varying Direction:
The direction of the unbalanced force, however, varies as the object rotates. This is because the distribution of mass around the axis of rotation changes as the object rotates. The unbalanced force will always act in the direction that opposes the change in rotational speed. As the object rotates, different parts of the mass distribution will experience different forces, resulting in a varying direction of the unbalanced force.

Example:
To illustrate this concept, let's consider a rotating bicycle wheel. When the wheel is initially at rest, there is no unbalanced force acting on it. However, when a force is applied to the pedal, the wheel starts rotating. As the wheel rotates, the distribution of mass around the axis of rotation changes, resulting in a varying direction of the unbalanced force. The unbalanced force will always act in the direction opposite to the change in rotational speed, providing the necessary torque to maintain or change the rotational motion.

Conclusion:
In conclusion, the unbalanced force due to revolving mass is constant in magnitude because the mass distribution remains the same. However, the direction of the unbalanced force varies as the object rotates, providing the necessary torque to maintain or change the rotational motion.