Assumptions - Box on Table

The applet shows forces and the corresponding reaction forces acting on the parts of a system consisting of a box that is resting on a table which in turn is resting on the earth.

The applet deals with forces exerted on the three parts of a system consisting of a box, a table, and the earth. Only forces exerted by the three parts of the system on each other are considered.

Forces exerted on a part of the system by objects outside the system are ignored, e.g., the forces exerted by the air on either the box or the table. Thus, forces of buoyancy are ignored. This is possible because these forces are small in comparison to the forces that are being included.

In representing the various forces by arrows of certain lengths, the applet assumes that the table's weight is twice that of the box.