Free Body Diagram - Example: A Block On An Inclined Plane

Example: A Block On An Inclined Plane

A simple free body diagram, shown above, of a block on a ramp illustrates this.

• All external supports and structures have been replaced by the forces they generate. These include:

• mg: the product of the mass of the block and the constant of gravitation acceleration: its weight.
• N: the normal force of the ramp.
• F_f: the friction force of the ramp.

• The force vectors show direction and point of application and are labeled with their magnitude.
• It contains a coordinate system that can be used when describing the vectors.

Some care is needed in interpreting the diagram. The line of action of the normal force has been shown to be at the midpoint of the base but its true location can only be found if sufficient further data is given. The diagram as it stands would need to be modified were we told that the block is in equilibrium.

There is a potential difficulty also with the arrow representing friction. The engineer who drew this diagram has used the tip of the arrow to indicate the point of application of a force. (See the other force arrows in the diagram). Now, the tip of the friction arrow is at the highest point of the base. The intention however is not to indicate that the friction acts at that point. The engineer in this instance has assumed a rigid body scenario and that the friction force is a sliding vector and thus the point of application is not relevant. The engineer has tried to indicate that the friction acts all along the whole base by drawing an arrow all along the base but such artistic ploys are a matter of personal choice.