( ( In equilibrium ) ( , ( ( ( the forces ) ( on ( the ( moving block ) ) ) ) ( ( must ( sum ( to zero ) ) ) . ) ) ) )
(ROOT (S (PP (IN In) (NP (NN equilibrium))) (, ,) (NP (NP (DT the) (NNS forces)) (PP (IN on) (NP (DT the) (VBG moving) (NN block)))) (VP (MD must) (VP (VB sum) (PP (TO to) (NP (CD zero))))) (. .)))
In equilibrium, the forces on the moving block must sum to 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)))))))))) (. .)))