What is Free Body Diagram?

A free body diagram is a diagram of a chosen system in which we represent all the forces acting on it and thus calculate the net force. These diagrams are used to show the direction and magnitude of all the forces acting upon an object. The length of the arrow represents the magnitude of the force and arrows are labelled to indicate the type of force. In a free body diagram, the object is generally represented as a box and the arrows representing force are drawn from the centre of the object. There is no strict rule on the number of forces that can be drawn in a free body diagram. An example of a free body diagram is given below.

Below are steps to draw a free body diagram:

  1. Understand the description of the physical system and represent it as a box.
  2. Use your understanding of the different types of forces to draw the forces acting on the body.
  3. Determine the directions in which the forces are acting and draw the forces with appropriate magnitude and direction.
  4. Write the name of the forces.

Let us understand the concept with the help of an example,

A block of mass 0.1 kg is held against a wall applying a horizontal force of 5N on the block. If the coefficient of friction between the block and the wall is 0.5, the magnitude of the frictional force acting on the block is?

Limiting frictional force = μsN = 0.5 x 5 = 2.5 N

The magnitude of frictional force acting on the body is f = 0.1 x 9.8 = 0.98 N.

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