In order to identify and label forces of a Free-Body Diagram, one must recognize the various types of forces that they will encounter and must know how these forces will interact with each other in order to calculate them.
Weight:
Any object with a mass is known as weight. It can be shown in pounds or Newton’s (N). If the weight is not given, it can be calculated in Newton (N) by multiplying the mass in kilograms (kg) with the Earth’s gravitational constant (9.8 m/s2).
Normal Force:
According to Newton’s Third Law, every action has an equal and opposite reaction. Due to this law, an object that rests on a surface, that is, an object that is not in free fall has a normal force acting in a perpendicular direction to the surface of the object on which it is resting. In the absence of any additional forces, the magnitude of the vertical component of the normal force is equal to the weight of the object.
Friction Force:
Friction force resists movement and always acts in the opposite direction of the movement or potential movement. It also acts parallel to the surface and is perpendicular to the normal force. The friction force is equal in magnitude to the force that provides the movement until and unless the opposing force exceeds the maximum friction force. The maximum friction force can be calculated by multiplying normal force by the surface coefficient of static friction.
Tension:
This force is the pulling force that is exerted on an object by a rope, chain, or cable. Tension force is continuous from one end to another. Because tension force is always continuous and a rope is flexible, pulleys can be utilized to redirect the rope and by extension, the tension force.
Applied Force:
Applied force is a force that is applied by a person or by some other object.
Free Body Diagram Examples
Now we will explain the FBD concept, using the following free body diagram example problem as shown in Fig. 1.
A 50 kg stationary box must be pulled up a 30 degree inclined by a pulley system. The coefficient of static friction between the box and that incline is 0.25. Assuming there is no friction in the pulley system, what force in Newton’s (N) must be applied to the rope in order to move the box up the incline?
