( ( If ( forces ( combine ( to ( ( a ( net force ) ) ( of zero ) ) ) ) ) ) ( , ( ( the object ) ( ( ( will not ) ( ( ( ( move , ) or ) just ) ( move ( at ( ( the ( same speed ) ) ( it ( had ( been ( moving at ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN If) (S (NP (NNS forces)) (VP (VBP combine) (PP (TO to) (NP (NP (DT a) (JJ net) (NN force)) (PP (IN of) (NP (CD zero)))))))) (, ,) (NP (DT the) (NN object)) (VP (MD will) (RB not) (VP (VP (VB move)) (, ,) (CC or) (ADVP (RB just)) (VP (VB move) (PP (IN at) (NP (NP (DT the) (JJ same) (NN speed)) (SBAR (S (NP (PRP it)) (VP (VBD had) (VP (VBN been) (VP (VBG moving) (PP (IN at)))))))))))) (. .)))
If forces combine to a net force of zero, the object will not move, or just move at the same speed it had been moving at.
(ROOT (S (NP (DT A) (VBG moving) (NN car)) (VP (VBZ is) (VP (VBN said) (S (VP (TO to) (VP (VB be) (PP (IN in) (NP (JJ dynamic) (NN equilibrium))) (SBAR (WHADVP (WRB when)) (S (NP (PRP it)) (VP (VBZ is) (NP (CD zero) (JJ net) (NN force)))))))))) (. .)))