( ( For ( work ( to occur ) ) ) ( , ( ( a force ) ( ( must ( ( produce motion ) ( in ( ( the direction ) ( of ( the force ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN For) (NP (NN work) (S (VP (TO to) (VP (VB occur)))))) (, ,) (NP (DT a) (NN force)) (VP (MD must) (VP (VB produce) (NP (NN motion)) (PP (IN in) (NP (NP (DT the) (NN direction)) (PP (IN of) (NP (DT the) (NN force))))))) (. .)))
For work to occur, a force must produce motion in the direction of the force.
(ROOT (S (NP (NNP Work)) (VP (VBZ is) (VP (VBN done) (SBAR (RB only) (IN if) (S (NP (DT a) (NN force)) (VP (VBZ is) (VP (VBN exerted) (PP (IN in) (NP (NP (DT the) (NN direction)) (PP (IN of) (NP (NN motion))))))))))) (. .)))