Unbalanced force occurs when two or more objects come together with a push or pull motion and one of those forces is stronger than the other. For example, in a game of tug-of-war, if the teams are paired unequally, then when the two teams begin to pull on each side of the rope, the stronger team will cause the flag in the middle to move toward the stronger side. If the two sides are perfectly matched in strength, then the flag wouldn't move at all.
Unbalanced force is used in a number of ways. For example, at an amusement park, unbalanced force is used to propel people through the air on various rides. The air velocity has its own level of force, however, if the thrust, or push, of the amusement park ride is greater than the force of the air while the ride is moving, it will continue to move forward. If the air velocity were as strong as the force of the amusement park ride, then the ride wouldn't be able to move.
The motion that unbalanced force creates can cause an object to move in the same direction as another or in an opposite direction. This occurs when more than one object applies force along with another, against an object. For example, several people pushing on a stalled car at the same time will cause the car to move in a single direction.
Unbalanced force is a result of a lack of equilibrium between two objects and when that occurs, the side with the stronger applied force will cause the side with the weaker force to accelerate. Gravity is an example of the acceleration that occurs from unbalanced force. Gravity exerts a pull force on every object on earth. An airplane can stay in the air because it is pulling harder than the force of gravity. However, if the airplane's upward thrust suddenly ended, then gravity would pull it downward, causing acceleration of the plane as it is pulled toward earth.