FF-1125 Equilibrium of Parallel Forces Apparatus


  • Verify the conditions of equilibrium when sets of parallel forces act in one plane on a rigid body Fv = 0 (where F = forces and V = vertical).
  • Special case where equal and opposite parallel forces produce a couple acting on a body.
  • Equilibrium of opposing couples.
  • Experimental verification of the use of a link polygon and is a test of M = 0 (where M = moments).


A force board is clamped into the Universal Frame and Stand. Two acrylic models engraved to simulate a ‘Warren’ and an ‘N’ truss are used for the application of vertical loads and reactions. The forces are produced with cords tensioned by weights on hangers, double pulleys being used to turn the up ward forces downward.

A circular disc with twelve attachment points is used for the couples. To simplify the results each acrylic model has a counter balancing weight to render each one ‘weightless’. The lines of action of the cords can be transferred onto a sheet of paper clipped to the force board. The set of weights needed for the experiment is included.