What is Free Body Diagram

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Free body diagram (FBD) is a graphical representation of the forces acting on a body of interest in given conditions. FBD helps in solving static and dynamic problems in mechanical engineering. We suggest you to also read this article on degree of freedom in mechanics.

Why We need Free Body Diagram ?

FBD help engineers in product design by providing the following information:

  • Visualize forces acting on a body.
  • Calculate unknown Forces.
How to Draw Free Body Diagrams ?

To under FBD, let’s consider a case when a man trying to push a 25 kg wooden block on wooden flooring. We will draw the FBD for the wooden block.

FBD of any system can be created in the following three steps:

Step-1: Identify and list down all forces acting on a body.

When a man tries to push a wooden block, he works against, wooden block weight and frictional force in between wooden block and floor. Therefore following forces acts on the block.

  • Weight of the object (W).
  • Frictional Force (f) in the direction opposite to movement of block.
  • Ground Reactive Force (R)
  • Push force by Man (F) (For this example we will consider man will apply normal force)
Step-2: Create Rigid Body line diagram

In this case line diagram for a rectangle block will be a rectangle. It defines the basic shape of the body.

Step-3:  Mark the forces acting on Rigid Body on Line Diagram

Draw FBD by drawing force vectors on rigid body line diagram. Force vectors are drawn using arrow in the direction of acting force.

As per Newton’s second law, in static condition all forces acting on a body makes it in equilibrium.

Free Body Diagram Examples
FBD For Running Person
FBD For Block Moving on Inclined Plane
FBD For Book on Table
FBD for Free Falling Ball
Conclusion

To sum up, FBD is a very good tool in physics and engineering to visualize and calculate the forces acting on a rigid body. 

Got Questions?  We will be happy to help.

If you think we missed Something?  You can add to this article by sending message in the comment box. We will do our best to add it in this post.


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