Balanced vs Unbalanced Forces

Introduction

In simple terms, force is just a way for two objects to interact. Its effect is that of a push or pull and it causes a change in the position and/or velocity of the object it is being applied on. The application of force also lends us the possibility of doing work as the object gets displaced.

Force is a vector quantity and thus, has both magnitude and direction. Therefore, for two forces to be truly equal, they must have the same magnitude and be applied in the same direction. When two forces of the same magnitude are applied on a body in opposite directions, they are said to be balanced. In such a case, the net force on the body is zero. An unbalanced force is encountered when the net force on the body isn’t zero.

What are Balanced Forces?

Balanced forces are those that act on a system with equal magnitude but in opposite directions. This results in a net force of zero on the system, causing it to remain in the state it was in (either at rest or in motion) with zero acceleration. In such a state, the body is said to be in equilibrium.

Example: Let’s consider four forces acting on the rectangular box the below diagram

Example of balanced forces.

The diagram attached below shows a rectangular box subject to four forces: 

• In the vertical direction, there is an upward force of 3 Newtons and a downward force of 3 Newtons. Since these forces are equal in magnitude but opposite in directions, they cancel each other out and result in no net force in the y-direction. 
• Similarly, the forces in the x-direction have equal magnitude but are in opposite directions, making them balanced as well. Thus, the rectangular box is experiencing balanced forces.

Examples of Balanced Forces

• Tug of war in which teams have equal members – The idea of tug of war is to pull the reference point on the rope beyond your line. However, if two identical teams were to play tug of war, they would exert identical forces on the rope, but in opposite directions. Thus, the rope would remain at rest and we have a state of balanced forces.
• Book on the table – A book when placed on a table is in equilibrium since its weight and the normal reaction due to the table cancel each other out.
• Person standing on the ground – When we stand still, we exert a force on the ground equal to our weight, and the ground exerts a normal reaction on us. Thus, we are in a state of equilibrium under balanced forces.

Characteristics of Balanced Force

• The state of rest or of motion of the body is not altered when it experiences balanced forces.
• A system under balanced forces is in static equilibrium.
• The net force on the system is zero when it is experiencing balanced forces.

Effect of a Balanced Force on a Body

When a body experiences balanced forces, the net or resultant force acting on the body is zero. This means that balanced forces do not cause any change in the state of the body. If the body is at rest, it will remain at rest under the balanced force, and if the body is in motion, it will continue to move at the same velocity.

What are Unbalanced Forces?

An unbalanced force is one that causes a change in the motion of a body. If the body is at rest, an unbalanced force can set it in motion and vice versa, if the body is already in motion, an unbalanced force can change its speed or direction. 

When two forces acting on a body have unequal magnitudes, the system is under unbalanced force. The resultant force on the body is not zero, resulting in non-zero acceleration and an absence of equilibrium condition.

Example: Suppose a book is placed on a table that has an incline. In that case, it will begin sliding down

A book placed on a table

In the vertical direction, the table experiences the vertical component of the book’s weight and applies a normal reaction on the book. These forces balance each other out, but in the horizontal direction, the frictional force cannot balance the horizontal component of the book’s weight and thus, the book begins to slide down.

Examples of Unbalanced Forces

• Tug of war in which teams have unequal members – For a tug of war game where the two teams aren’t identical, one of them will apply a larger amount of force and end up winning the same.
• See saw the game – Since the two people sitting on the see-saw don’t have identical weights, this is an example of unbalanced force. 
• Kicking a ball – A ball receiving a kick receives an unbalanced force.

Difference between Balanced and Unbalanced Forces

Summary

This article explains the concept of forces and their two main types: balanced and unbalanced forces. Balanced forces do not affect the state of an object, whereas unbalanced forces are responsible for its motion. 

A body under the effect of balanced forces experiences no net acceleration or force, but unbalanced forces can cause net acceleration in the system. Another major difference is that balanced forces can only alter the geometry (shape or size) of the object, whereas unbalanced forces can also alter its state of motion.

Frequently Asked Questions

1. What are the possible states of motion?

The two states of motion are as follows:

1. A body can remain at rest, which is when it has no motion with respect to a reference point.
2. The second state is that of motion wherein, the body is moving with a certain velocity.

2. Can a balanced force deform a body?

Yes. While movement isn’t possible due to balanced forces, the geometry of the object can get altered.

3. Given acceleration, how do we find force?

According to Newton’s second law, force is equal to mass times the acceleration. That is,

F=ma

4. What unit is force measured in?

The S.I. unit of the force is newton or \({kgms^{-2}}\). In C.G.S. system, it is dyne or \({gcms^{-2}}\).

5. Give one daily life example of balanced force.

Screws or clips experience frictional force from the wall. This allows us to hang items on the walls which experience balanced forces and thus, do not fall down.