Free Body Diagram
A graphical representation used to analyse the forces exerted on objects by other objects. Below are the steps to follow to draw the free-body diagram of a box that you push along a smooth surface.
Step 1. Draw a sketch of the situation described in the problem.
Step 2. Circle the object (objects) of interest in the sketch. This is called the system. (In this example the system contains only one object: 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 (no rotation) you can think as the object as a point particle. Draw a dot to represent the object.
Step 4. Identify the objects outside the system (external objects) that interact with the system. Decide what objects are relevant and what objects are not. (In this example are the surface, the Earth and You "pushing").
Step 5. Draw arrows representing the forces originated by the external interactions that affect the behavior of the system object. Draw the tails of these arrows beginning on the particle dot. The lengths of the arrows should 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, FYou on Box, means the force that You exert on the Box).
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