( ( If ( ( two ( or ( more forces ) ) ) ( act ( on ( an object ) ) ) ) ) ( , ( ( ( then ( the ( net force ) ) ) ( acting ( on ( the object ) ) ) ) ( ( is ( ( the ( vector sum ) ) ( of ( all ( the forces ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN If) (S (NP (CD two) (CC or) (JJR more) (NNS forces)) (VP (VBP act) (PP (IN on) (NP (DT an) (NN object)))))) (, ,) (NP (NP (RB then) (DT the) (JJ net) (NN force)) (VP (VBG acting) (PP (IN on) (NP (DT the) (NN object))))) (VP (VBZ is) (NP (NP (DT the) (NN vector) (NN sum)) (PP (IN of) (NP (PDT all) (DT the) (NNS forces))))) (. .)))
If two or more forces act on an object, then the net force acting on the object is the vector sum of all the forces.
(ROOT (S (NP (NP (NNS Objects)) (PP (IN on) (NP (NN earth)))) (VP (VBP have) (NP (NP (CD two) (NNS forces)) (VP (VBG acting) (PP (IN on) (NP (PRP them))) (PP (IN at) (NP (DT all) (NNS times)))))) (. .)))