Free-body Diagram

The visual representation of all the forces acting on the particle is called a free-body diagram or force diagram. It transforms complex problems into simple representations.

In a free-body diagram, the direction of the arrows indicates the direction of forces, while the arrows' length represents the magnitude of the forces.

Consider a stationary trolley on which two cardboard boxes are stacked.

Here, the two systems of interest, box one and box two, can be assumed to be isolated systems and can be represented using a free-body diagram in the form of a simple outline or a dot.

The forces acting on box one are the gravitational force, which defines its weight, and the counter-balancing normal force due to box two.

Similarly, the forces on box two are its own weight, the normal force due to the trolley, and the weight of box one.

Free-body diagrams play an integral part in the problem-solving process as a transition from a specific physical situation to an abstract mathematical equation in mechanics.