( Equilibrium ( ( exists ( if ( ( the ( net force ) ) ( is zero ) ) ) ) . ) )
(ROOT (S (NP (NNP Equilibrium)) (VP (VBZ exists) (SBAR (IN if) (S (NP (DT the) (JJ net) (NN force)) (VP (VBZ is) (NP (CD zero)))))) (. .)))
Equilibrium exists if the net force is zero.
(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)))))))))) (. .)))