If you know all of the forces acting on a moving object,

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If there are four forces acting on an object, the resultant forces will be added up. When one vector is equal in magnitude but opposite in direction of another vector, the two cancel each other. When all the forces acting on an object do not cancel out, the force is said to be unbalanced. The sum of the unbalanced forces is the net force, and the net force results in acceleration, or the increase of velocity. Force is measured in newtons. If an object is acted upon by an upward vector of 40 newtons and a downward vector of 10 newtons, the resulting net force is 30 newtons upward. The net force or resultant force acting on a resting or moving body is the vector sum of all the forces acting on that object.