What is Resolution of Forces?

By Aina Parasher|Updated : August 26th, 2022

Force is the action of one body on another. It is a physical quantity that can change the state of motion of a body. Force is a vector quantity. In this particular article, we are going to discuss the resolution of forces. Resolution of forces is a process of splitting the forces or dividing the forces into two or more parts which ultimately creates the same effect on the body that the single force would have created. 

Resolution of forces helps us in analyzing motion separately in different directions. It is very essential in some cases to analyze the effect of forces in different directions. In all such cases, resolution of forces is required.

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Table of Content

What is the Resolution of Forces?

Resolution of forces is essentially the technique by which a given quantity of force is divided into a variable number of components; it is done in such a way that the effect on the body remains constant. In general, it is done in two mutually perpendicular directions.

Resolution of Forces into Components

The process of splitting up a given force into different components without changing its effect on the body is called the resolution of a force. If a force 'F' is resolved or replaced by two forces using the principle of resolution of forces, it will together produce the same effect as that of force 'F'. These forces are known as the components of the force 'F'.

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Resolution of Forces into Rectangular Components

The rectangular component of any force is two components such that they are perpendicular to each other, and the resultant of the two components will give the resultant force. Let us consider a force 'F' inclined at an angle 'θ' to the horizontal as shown in the figure below. X and Y are two axes passing through 'O' and perpendicular to each other.

Rectangular components

Applying the principle of resolution of forces, resolve the force 'F' into Fx and Fy. The polygon constructed with these two components as adjacent sides will form a rectangle OABC, therefore, the components are known as rectangular components. For the sign convention of components of forces, conventional co-ordinate directions are considered.

X-component (Fx)→Positive

←Negative

Y-component (Fy) ↑ Positive ↓ Negative

Example:

Determine the X and Y components of the force shown in the figure.

Rectangular components examples

Solution:

Consider the triangle OAB,

cos θ = OA/OB

OA = OB cosθ

OA = Fx

OB = F

Fx = F cosθ

Sin θ = AB/OB

AB = OB sinθ

AB = Fy

OB = F

Fy = F sinθ

The two rectangular components of the force 'F' after resolution of force are:

Fx = F cosθ

Fy = F sinθ

Applying the principle of the resolution,

1. Component along X-direction

Fx = 20 cos30°

Fx = 17.32N

2. Component along Y-direction

Fy = 20 sin30º

Fy = 10N

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Triangular Parallelogram Law of Forces

In the Triangular Law of Forces, If two forces acting simultaneously on a body are represented in magnitude and direction by two sides of a triangle in order, then the third side represents the resultant of the two forces in the opposite direction and magnitude.

Triangular

The resultant of two concurrent and coplanar forces, i.e, forces lying in the same plane whose line of action passes through a single point may be obtained using the theorem of the parallelogram of forces which states that "If two forces acting at a point are represented by the sides of a parallelogram drawn from the point in magnitude and direction, their resultant force is represented by the diagonal of the parallelogram drawn through that point in magnitude and direction."

Parallelogram

Resolution of Forces MCQs

1. A force of 50N is acting at a point making an angle 35o with the horizontal. Determine the components of this force in X and Y directions.

FAQ

Component along X-direction

Fx = 50 cos 95o = 40.95N

Component along Y-direction

Fy = 50 sin 35o = 28.68N

2. Find the resultant for the given force system using the principle of superposition of forces. 

FAQ 2

∑Fx = 0

30 + 15 cos 60o – 25 cos 30o = 15.85N

∑Fy = 0

50 + 15 sin 60o + 25 sin 30o = 75.5N

Resultant Force (R) = √(Fx2+ Fy2)

= 15.852+ 75.52

= 77.15N

3. Resolve the 400 N force acting on a block as shown into horizontal and vertical components.

FAQ 3

Angle of inclination of 400 kN force with respect to horizontal x-axis = 40o-20o = 20o

Component along Horizontal axis = 400 cos 20o = 375.35N

Component along Vertical axis = -400 sin 20o = -136.8N

Important Topics for Gate Exam
Non-Newtonian FluidsOpen Loop Control System
Pattern AllowancesPoissons Ratio
Pressure MeasurementPrestressed Concrete
Prestressing SystemsPrinciple of Conservation of Energy
Properties of AggregateProperties of Concrete

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FAQs on Resolution of Forces

  • When a force is divided into two along two mutually perpendicular directions, the parts along those directions are referred to be resolved parts without modifying its impact on the body. This procedure is known as the resolution of force.

  • If two forces acting at a point are represented, in magnitude and direction by the sides of a parallelogram drawn from the point, their resultant force is represented, both in magnitude and in direction, by the diagonal of the parallelogram drawn through that point.

  • Through the use of trigonometry or a graphic representation, a force can be divided into two component forces. Resolution of forces allows us to analyze causes of motion separately in vertical, mediolateral, and anteroposterior axes individually.

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