An unbalanced force is a force that, when resolved into vector components, will not cancel out, creating some net force (or a force component) on the object. Hence, when an unbalanced force is applied to an object, Newton's laws of motion are applicable. According to the first law, the applied force will likely change the state of the motion of the object. If the object was at rest, it may cause it to move (provided sufficient force is applied). If the object was in motion, the force may aid or inhibit the motion or change the direction of the object. The acceleration of the body, as a result of this unbalanced force, can be calculated using the second law of motion.
Hope this helps.
An unbalanced force refers to when the sum total of the forces acting on an object do not equal zero. There are many scenarios where this may happen. For example, when a book is pushed across the table. The normal force and the gravitational force is equal. However, an unequal force is applied in the right direction of the object, causing the object to move. In other words when a force is unbalanced it will cause the object to have acceleration and move. This is further proved with Newtons second law - F=MA. Since force does not equal zero and the object has mass then there must be acceleration as well.