equilibrium force   Concepts covered: The Net Force| Resultant Forces The Net Force The force that is the resultant force of all forces acting on a body is defined as the net force. If the vector sum of all the forces acting on an object is equal to zero, then the object is in equilibrium. Resultant force Resultant forces cause objects to accelerate. If an object is stationary or moving at constant velocity then either: • No forces are acting on the object, or • The forces acting on that object are exactly balanced. A resultant force would cause a stationary object to start moving or an object moving with a given velocity to speed up or slow down or change direction such that the velocity of the object changes. For stationary objects or objects moving with constant velocity, the resultant force acting on the object is zero. The object is said to be in equilibrium. If a resultant force acts on an object then that object can be brought into equilibrium by applying an additional force that exactly balances this resultant. Such a force is called the equilibrant and is equal in magnitude but opposite in direction to the original resultant force acting on the object. reference http://www.tpub.com/content/doe/hdbk1010/css/hdbk1010_116.htm http://hypertextbook.com/physics/mechanics/statics/ http://en.wikibooks.org/wiki/FHSST_Physics_Forces:Equilibrium_of_Forces