EM-106.01 | Polygon of Forces Apparatus

This apparatus is majorly a round disc which is placed horizontally on three legs attached to a foundation. A 360 protractor is set centrally on the plate and pulleys on clamps permit the load hanger cords to run toward a ring dropped over the center. The apparatus is best to express the conditions of equilibrium of coplanar forces acting on a circular disc. Conditions of equilibrium can be obtained by centralizing a small ring available over the central pin with cords to load hangers where the loads and lines of action are variable. In this way, it is possible to construct the multiple of forces in equilibrium and to find the resultant forces. A simple but elegant demonstration of the conditions of equilibrium for three or more coplanar forces acting either at a point, on a circular disc or on a rectangular shape. Up to five loads can be applied to the chosen shape by setting up pulleys at various angular positions. The lines of action of the forces are recorded by drawing along the weighted cords onto a piece of paper attached to the pulley table. A range of experiments is possible, investigating concurrent and non-concurrent coplanar forces acting on simple shapes, comparing the experimental values with the relevant polygons of force. A complete instruction manual is provided describing the apparatus, its application, experimental procedure and typical test results.

Learning Objectives

• To resolve by experiment any suitable system of static coplanar forces which may or may not be concurrent.
• To verify graphically using:
• Triangle of forces for three or more than three concurrent coplanar forces.
• Polygon of forces for more than three concurrent coplanar forces.
• Link polygon for three or more non-concurrent coplanar forces
• To investigate (c) for either a disc or a rectangular shape.
• To compare the accuracy of the experiment by comparing the experimental and graphical results.