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Free Body Diagrams
A free body diagram is a visual representation of all the forces acting on an object. It is a simple way analyze the dynamics of an object by deconstructing all the forces acting on an object and studying the object as if it were in isolation. Let us understand how to draw a free body diagram for any system:
A free body diagram is a visual representation of all the forces acting on an object. It is a simple way analyze the dynamics of an object by deconstructing all the forces acting on an object and studying the object as if it were in isolation. Let us understand how to draw a free body diagram for any system:
- Observe the object under consideration. Draw the object with its basic geometry, without any details, such that it is isolated from all elements around it.

2. Now list all the external forces directly acting on the body. A free body diagram does not include internal forces of an object. External forces like, weight, reaction force, friction etc. are to be included in the free body diagram.
3. Represent all these forces acting on the objects as vectors with their correct orientation along with the object.
3. Represent all these forces acting on the objects as vectors with their correct orientation along with the object.
Note: Any acceleration possessed by the body is not to be included in the free body diagram as the acceleration arises from all the forces seen in the free body diagram being unbalanced.

Sample Problems:
A point on a sphere of weight rests in contact with a smooth vertical wall and is supported by a string joining a point on the sphere to a point on the wall. Draw a free body diagram of the sphere.
A rod OA is suspended with help of a massless string AB as shown in figure. Rod is hinged at point O. Draw free body diagram of the rod.
A helicopter is moving to the right at a constant horizontal velocity. It experience three forces , and force on it caused by rotor . Which of the following diagrams can be a correct free-body diagram representing force on the helicopter?