Physics

Balanced force-Definition|Examples

Force is all around us in this world. The revolution of the earth around the sun, moon around the earth, or objects coming to a stop, etc are all examples of force. In any given case there might be multiple types of forces acting on a body in multiple directions. To understand balanced and unbalanced forces we have to look at all the forces acting on a body. In this article, we focus on building a definition for balanced force and unbalanced force using everyday examples and force diagrams.

For example, when we walk, muscular force, air resistance, dry friction, and gravitational forces are acting upon us at the same time. The net resultant force allows us to move forward.

Based on the magnitude and direction of the net force acting on a body, the forces can be classified into two categories as balanced force and unbalanced force.

Newton’s first law of motion

It states that an object in uniform motion will continue to be in uniform motion unless acted upon by an external force. And an object in rest will continue to be in rest unless and until acted upon by an external force.

Balanced force definition:

A balanced force is a situation when two forces acting on a body are equal in magnitude but opposite in direction. The equal and opposite forces cancel out each other. Hence a body in a state of rest will remain in rest. And, a body in motion will remain in motion.

Balanced forces cannot change the state of motion or the direction of motion.
They can change the shape of the object.
The body under the influence of balanced forces will continue to be in its initial state of motion. The forces cancel out each other due to their opposing direction.

Force diagram of balanced forces:

Explanation of balanced forces — Force diagram showing the equal and opposite forces

Normal force: an example of action-reaction balanced forces — Force diagram of an action-reaction example

Examples of balanced forces:

The weight of an object and the normal force acting on a body are balanced. The weight acts in the downward direction due to gravity, and the normal force acts in the opposite direction with equal magnitude.
A car that is pushed from opposite sides with equal force. The car will remain in its state of rest only. It will never move.
A lizard on a wall in a vertical position. The weight of the lizard should pull it down due to the force of gravity. But, the force of friction balances it out with an equal magnitude force.
A ball hanging by a rope. The weight of the object is balanced by the tension provided by the rope. The tension is equal and opposite.
A weighing balance where the weight in both of the pans is exactly equal.
Cruise control in a car. The car is maintained at a uniform speed due to balanced forces.
Equally matched opponents in a game of arm wrestling.
An airplane in steady wings level flight is in equilibrium. The lift of the airplane is balanced by the weight and the thrust is balanced by the drag.

Example of balanced forces: Resting against a wall

Most of the examples of balanced forces can be categorized into a few categories. Let us look at each one of these in detail.

Action-reaction forces:

For every action, there is an equal and opposite reaction. So the forces here are equal in magnitude and also opposite in direction. So, these forces can qualify for examples of balanced forces. Some examples in this category include:

Normal force against the ground is generally equal to the weight of the object but in the opposite direction. The weight of the object and the normal force cancel each other out.
When we push a wall and nothing happens. The wall provides a reaction force in the opposite direction to counter our force.

Tension in a rope

The tension developed in a rope or a string is always equal and opposite to the load attached to it. Examples include:

Ball hanging in a rope. The tension in the rope will keep the ball stationary. The tension is equal and opposite to gravitational force.
Apple hanging in a tree. The weight of the apple is balanced by the tension in the tree branch.
In an intense game of tug of war, when the force applied by both teams is equal. After some time, generally, the forces become unbalanced due to differences in the stamina of the two teams.

Floating in water

Why do objects float in water? It is because the water provides an upthrust force that is equal and opposite to gravitational pull. According to the Archimedes principle, the buoyant force is equal to the weight of the water displaced by the object. So, the minimum condition for floating is that the weight of the object must be equal to the weight of water displaced.

Static Friction

Static friction is a self-adjusting force that adjusts itself so that it is equal and opposite to the force applied on an object at rest. Hence, the object will not move until the force applied is greater than the limiting friction, beyond which the forces become unbalanced. Examples include

Brick on a table. It will not move with the slightest push because the static friction adjusts itself to be equal and opposite.
A car parked on a hill. Since the cars are parked at an incline the gravitational force should ideally pull them or slide them down. But the static force of friction provides an equal and opposite force to keep them in a state of rest.

Unbalanced force definition:

When two forces act upon a body in the same direction or in opposite direction with unequal force then they are said to be unbalanced. The net force is non-zero in this case. The value of the net force will cause a change in shape, direction, or state of motion. It can also increase or decrease the speed of an object in motion.

Example of unbalanced forces: Pushing an object to set it in motion

Forces are not opposite in direction, then both the forces will be added together to form a stronger force in the intended direction.
If the forces are opposite in direction but unequal then the net force will push the object in the direction of the net force. You can understand this by seeing the image below.
When the forces are at different angles, the net resultant force will be acting on the body.

Force diagram of unbalanced forces:

Explanation of unbalanced forces — *Force diagram of different scenarios for unbalanced forces*

Examples of unbalanced forces

Seesaw with a heavier person on one side.
Hitting a baseball with a force.
Accelerating the speed of the car.
Unmatched opponents in a game of tug of war or arm wrestling.
An object drowning in water.
A turning aircraft, where both the direction and the speeds change.

Example of unbalanced force, baseball being hit. — The baseball is struck at a force by the bat. Since there is no force to balance from the opposite direction the force is unbalanced. Hence the ball will move in the forward direction.

What is the difference between balanced and unbalanced forces?

Balanced forces	Unbalanced forces
Forces are equal and opposite	Forces are not equal and opposite
They cannot change the state of motion	They can change the state of motion
They cannot change the direction of a moving body	They can change the direction of a moving object
They cannot change the speed of a moving object	They can change the speed of a moving object

Difference between balanced and unbalanced forces

Research:

Researchers have designed a microrobot that moves in the microfluidic environment by using balanced magnetic and buoyant forces. The robot could grip a microsized particle and deliver it in a 3D space. [Link: https://www.mdpi.com/2072-666X/9/2/50]

In this article researchers have designed a chip for small-sized human-like robots. In the presence of an external force, the robot might lose its balance. So, the angle of inclination of the robot is detected by a gyroscope and an accelerometer. The experimental results presented in this article show how the robots use a balance control method to avoid falling down due to unexpected external forces. [Link:https://www.mdpi.com/2076-3417/10/8/2699]