Free Body Diagram - Characteristics, Advantages, and Steps to Draw.

By Aina Parasher|Updated : May 3rd, 2022

A Free Body Diagram is a diagrammatic representation of a body or a system that is isolated from the surroundings. It indicates all the forces acting on the body. It comes in very handy while visualizing the forces & moments acting on the body or system. A free Body Diagram is a graphical representation of the applied forces, moments, and consequent reactions on a body in a particular situation. 

Free Body Diagram shows a body or a group of bodies, as well as all the applied forces, moments, and reactions that operate on the body. The main purpose of the Free Body Diagram is to visualize the forces and to calculate reactions. In this article, we will discuss different characteristics and important steps involved in drawing Free Body Diagrams. 

Table of Content

What is a Free Body Diagram?

A Free Body Diagram is a diagram that simplifies a component or system of components to the loads and moments applied to them. A Free Body Diagram is required to find and evaluate different forces acting on a body whenever it is in equilibrium. These diagrams are widely used to compute internal forces within a building as well as to determine the loading of particular structural components. 

The Free Body Diagram plays a very important role in visualizing and calculating resultant forces. The interaction forces and/or moments assigned to the now opened-up body must follow Newton’s Third Law. The body of interest and the external forces operating on it is represented by an FBD. 

  • The body: Depending on the type of body (particle/ extended, rigid/ non-rigid), and the questions to be addressed, this is generally a schematic. 
  • External forces: It is denoted by arrows with labels. A force arrow might indicate the path of action and its direction, the magnitude, and the application point.

Essential Characteristics of Free Body Diagram

Students can use a Free Body Diagram to envision an issue in its entirety or to understand a specific element of a more complex problem. So, in a nutshell, FBD is a fantastic tool for visualizing and solving engineering challenges.

There are some important points regarding Free Body Diagrams. A Free Body Diagram is a diagram or sketch of the selected system or body isolated from the surroundings. The system is shown completely isolated from all the other bodies including the foundation, support, etc. Interaction in the system by each body is removed in the isolated system.

Steps Involved in Drawing a Free Body Diagram

Free-body diagrams depict the magnitude and direction of all forces operating on an item in a given condition. The amount of the force is represented by the size of the arrow in a free-body diagram. The arrow indicates the direction in which the force is acting. Each force arrow in the diagram is identified with the sort of force it represents.

First of all selection of a system is necessary. Then, we need to identify all the forces acting on the isolated body or system. We need to choose the direction of forces and coordinate system. Resolve the forces along these axes and write the equilibrium equations. After writing all the necessary equilibrium equations, we need to find out the required unknown forces.

Advantages of a Free Body Diagram

Drawing a free-body diagram is a crucial step in addressing mechanics issues because it allows you to see all of the forces operating on a single item. In order to apply Newton's Second Law to the motion of an item, the net external force acting on it must be determined.

There are many advantages of drawing Free Body Diagrams. It is a medium to convert ideas into a physical model. It also helps in understanding all facts of a problem. It assists to build up suitable mathematical equations between various forces acting upon a link.

Examples

While drawing the Free Body Diagram, all the supports of the body are removed and replaced with reaction forces acting on it.

Simply Supported Beam

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Equations of Equilibrium

Fx = 0

Fy = 0

M = 0

Free Body Diagram Problems 

  1. Two bodies of masses 10kg and 20kg are connected together with the help of string are placed on a horizontal smooth surface. The body of 10kg is pulled by 600N force. Find the Tension in the string.                                                                                 (Ans – 400N)
  2. Find the tension in three strings A, B & C from the below-given figure. 

(Ans – TA = 400N, TB = 500N & TC = 300N)

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FAQs

  • Free-Body Diagram is given as a graphic, dematerialized, symbolic representation of the body (structure, element, or segment of an element) in which all connecting “pieces” have been removed. It is a diagrammatic representation of a body or a system that is isolated from the surroundings.

  • Free Body Diagrams represent the relative magnitude and direction of all forces acting upon an object in a given situation. It basically represents all the different types of forces and moments acting on a body after isolating it from its surroundings.

  • While drawing a Free Body Diagram, we draw the object of interest by drawing all the forces acting on it and resolve all force vectors into x– and y-components. Separate diagrams should be drawn for each object in the problem. We need to choose the direction of forces and coordinate system. Resolve the forces along these axes and write the equilibrium equations. After writing all the necessary equilibrium equations, we need to find out the required unknown forces.

  • Free Body Diagrams are used to visualize the forces and moments applied to a body and to calculate the resulting reactions in many types of mechanics problems. It is a diagrammatic representation of a body or a system that is isolated from the surroundings. It shows all the forces acting on the body.

  • A Free Body Diagram is a valuable tool for depicting and evaluating all of the forces that operate on a body in order to establish equilibrium or acceleration according to Newton's first and second laws.

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