Free Body Diagram

A free-body diagram is a graphical representation used to analyse the forces exerted on objects by other objects. Below we show the steps that you need to follow to draw the free-body diagram of a box that you push along a smooth surface.

Follow the steps of the procedure in the order indicated.

Step 1. Draw a sketch of the situation described in the problem.

Step 2. Circle an object (objects) of interest in the sketch. This is called the system. (In this example is the box.)

Step 3. If the object in the system is small compared to other objects in the situation being described or if all of its points move in the same way you can model the object as a point particle. Place at the side of the sketch a "particle" dot to represent the system.

Step 4. Look for objects outside the system (external objects) that interact with the system. Decide what objects are important and what objects are not. (In this example are the surface, the Earth and You).

Step 5. Draw force arrows that represent the external interactions that affect the behavior of the system object. Draw the tails of these force arrows beginning on the particle dot. Draw the lengths of the arrows to represent the relative magnitudes of the forces.

Step 6. Label the forces in the diagram. Identify the external object that causes each force and also the object on which the force is exerted. A good habit is to use clear labels indicating the object outside the system that is exerting the force on the object inside the system. (In this example, F_{You on Box}, means the force that You exert on the Box).