Short Answer:

An unbalanced force is a force that causes a change in the state of motion of an object. When two or more forces acting on a body are not equal in magnitude and opposite in direction, they are said to be unbalanced. These forces result in acceleration, change in speed, or change in direction of the object.

For example, when a person pushes a stationary car and it starts to move, it happens because the applied force becomes greater than the opposing frictional force. Thus, an unbalanced force always produces motion or change in motion of a body.

Detailed Explanation:

Unbalanced Force

An unbalanced force is a force that changes the motion of an object. It occurs when the total or net force acting on an object is not zero. In other words, when two or more forces act on a body and their magnitudes and directions are not the same, they do not cancel each other, and the resultant force remains. This resultant force is responsible for changing the speed, direction, or shape of the body.

Balanced forces do not cause motion because their effects cancel out. But unbalanced forces cause acceleration or deceleration. According to Newton’s First Law of Motion, a body remains at rest or continues to move at a constant velocity unless acted upon by an external unbalanced force. Therefore, unbalanced forces are the cause of all motion.

For example, when you kick a football lying on the ground, it moves because the force of your kick is greater than the frictional force between the ball and the ground. The extra force makes the ball accelerate, showing that the forces acting on it are unbalanced.

Nature of Unbalanced Forces

Unbalanced forces can act on an object in different ways depending on their direction and magnitude.

• When an unbalanced force acts in the same direction as the object’s motion, it increases its speed.
• When it acts in the opposite direction, it slows down or stops the object.
• When it acts at an angle, it changes the direction of motion.

Hence, unbalanced forces can cause:

1. A stationary body to start moving.
2. A moving body to speed up or slow down.
3. A change in the direction of a moving body.
4. A change in the shape of an object (in some cases).

Mathematical Representation

The unbalanced force acting on a body can be calculated using Newton’s Second Law of Motion, which states:

where,

•  = net unbalanced force acting on the object (in newtons)
•  = mass of the object (in kilograms)
•  = acceleration produced (in meters per second squared)

This means that the acceleration of an object is directly proportional to the unbalanced force acting on it and inversely proportional to its mass. If no unbalanced force acts (F = 0), there will be no acceleration and the body will remain at rest or move uniformly.

Examples of Unbalanced Forces

1. Pushing a Stopped Car:
   When you push a car, it remains at rest until your pushing force becomes greater than the frictional resistance. Once that happens, the car moves forward, showing unbalanced force in action.
2. Falling Object:
   When an object is dropped from a height, the gravitational pull of the Earth acts downward. Since there is no equal opposing force, the body accelerates downward due to an unbalanced force (gravity).
3. Playing Tug of War:
   When one team pulls with greater force than the other, the rope moves in their direction. The difference in forces creates an unbalanced condition.
4. Moving a Toy Car:
   When a child pushes a toy car on the floor, it moves forward because the pushing force is greater than friction.
5. Vehicle Acceleration or Braking:
   When a driver presses the accelerator, the engine’s force exceeds the resisting forces (air drag, friction), causing acceleration. When brakes are applied, the braking force becomes greater and slows the vehicle down.

Effects of Unbalanced Forces

1. Change in Motion:
   The most common effect is starting or stopping an object’s motion.
2. Change in Speed:
   The object may speed up or slow down.
3. Change in Direction:
   For example, when a car takes a turn, an unbalanced force acts towards the center of the curve.
4. Change in Shape:
   Unbalanced forces can deform soft objects like clay or rubber when compressed or stretched.

Difference Between Balanced and Unbalanced Forces

• Balanced Force:
  The forces are equal in magnitude and opposite in direction, resulting in no motion. Example: A book lying on a table.
• Unbalanced Force:
  The forces are unequal; hence, they produce a resultant force that causes acceleration or motion. Example: A rolling ball slowing down due to friction.

Applications of Unbalanced Forces in Engineering

In mechanical engineering, the concept of unbalanced forces is important in understanding vibration, motion, and system stability. For instance:

• In engine crankshafts, unbalanced forces can cause vibration, which is why balancing is necessary.
• In rotating machinery, uneven mass distribution produces unbalanced centrifugal forces.
• In aerodynamics, lift and drag forces are unbalanced to make aircraft rise or descend.

Understanding unbalanced forces helps engineers design safer and more efficient machines by minimizing vibration and improving performance.

Conclusion

An unbalanced force is the main reason behind any change in the motion or state of a body. It occurs when the forces acting on an object are unequal and do not cancel each other. This net force causes acceleration, deceleration, or change in direction. In mechanical systems, managing unbalanced forces is crucial to prevent vibration, wear, and failure. Therefore, understanding unbalanced forces is essential for designing stable and smooth-operating machines.