Free body diagram

A diagram or sketch of the body in which the body under consideration is freed from the contact surface (surrounding) and all the forces acting on it (including reactions at contact surface) are drawn is called free body diagram. Free body diagram for few cases are shown in below

Procedure of drawing Free Body Diagram

To construct a free-body diagram, the following steps are necessary:

Draw Outline Shape

Imagine that the particle is cut free from its surroundings or isolated by drawing the outline shape of the particle only

Show All Forces

Show on this sketch all the forces acting on the particle. There are two classes of forces that act on the particle. They can be active forces, which tend to set the particle in motion, or they can be reactive forces which are the results of the constraints or supports that tend to prevent motion.

Identify Each Force

The forces that are known should be labelled complete with their magnitudes and directions. Letters are used to represent the magnitudes and directions of forces that are not known.

Method of Problem Solution

Problem Statement

Includes given data, specification of what is to be determined, and a figure showing all quantities involved.

Free-Body Diagrams

Create separate diagrams for each of the bodies involved with a clear indication of all forces acting on each body.

Fundamental Principles

The six fundamental principles are applied to express the conditions of rest or motion of each body. The rules of algebra are applied to solve the equations for the unknown quantities.