Free Body Diagram | Why Free Body Diagram Is Used | How To Draw Free Body Diagrams?| Rules for Drawing Free Body Diagrams
Free Body Diagram | Why Free Body Diagram Is Used | How To Draw Free Body Diagrams?
Free Body Diagram :
Free Body Diagram is a simple schematic representation of various forces acting on an object when it is moving or stationary. A free body diagram is used to calculate static and dynamic forces acting on an object.
Why Free Body Diagram Is Used?
- To find out forces acting on a body
- To find the direction of forces acting on a body
- To simplify the model for easy analysis
- To find relative forces acting on a body like frictional forces.
Let’s take an example of a car that is moving uphill. To calculate how much force is required to push the car uphill, a free body diagram can be used.
Let’s take another example of designing a leveler leg of a refrigerator. To design those legs, we need to know how much force the refrigerator is putting on the ground. Based on that, we can design the leg. A free body diagram can be used to calculate that load.
How To Draw Free Body Diagrams?
Let us take an example to draw the free body diagram. Let us assume that you are trying to push a block that is lying on the ground. To calculate the forces acting on that body we will use a free body diagram.
Step-1 : Identify all forces acting on the body
In this example following forces are acting on the body.
- Weight of the block ( W) is the product of mass and gravitational force
- Reaction force or normal force ( R)
- Push force ( P)
- Friction force ( F)
Step-2 : Draw the schematic of the body
Draw the shape of the body and all other surfaces in the simplest form possible. Typically we use a rectangle when there are four sides of a body and for a circular shape, we use a circle. But frankly speaking, there is not such a role. It is the rule of the engineer to draw the diagram as simple as possible.
Step-3 : Show all forces with directions
Once the body is drawn, the next step is to draw force vectors to show how forces are acting. Use proper directional arrow for representation.
tep-4 : Calculate forces
The final step is to calculate the value of all those forces which are not known.
Rules for Drawing Free Body Diagrams:
Similarly to the steps rules must be taken into account while drawing free body diagrams. The following rules must be followed:
- Use a dot or box to represent the object: Always use a box or dot to represent the object.
- Only include pure forces: Trigonometric functions such as sin, cos, and tan should not be included in the drawing.
- Use length of arrow to represent relative magnitude of forces: The lengths of the arrows should correspond with the size of the forces, but not necessarily drawn to scale. Larger forces should be represented with longer arrows than smaller forces.
- Include a coordinate system: The direction in which the forces are applied must be distinguished. Forces can be applied in several directions.
- Exclude vectors like acceleration vectors (unbalanced forces)
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