( ( that ( is ( to say ) ) ) ( , ( ( ( the force ) ( exerted ( by ( ( one particle ) ( on ( ( another results ) ( in ( the latter ) ) ) ) ) ) ) ) ( ( 's ( changing ( ( ( ( ( ( ( the direction ) ( of ( its motion ) ) ) , ) ( ( the magnitude ) ( of ( its speed ) ) ) ) , ) or ) both ) ) ) . ) ) ) )
(ROOT (S (SBAR (WHNP (WDT that)) (S (VP (VBZ is) (S (VP (TO to) (VP (VB say))))))) (, ,) (NP (NP (DT the) (NN force)) (VP (VBN exerted) (PP (IN by) (NP (NP (CD one) (NN particle)) (PP (IN on) (NP (NP (DT another) (NNS results)) (PP (IN in) (NP (DT the) (NN latter))))))))) (VP (VBZ 's) (VP (VBG changing) (NP (NP (NP (DT the) (NN direction)) (PP (IN of) (NP (PRP$ its) (NN motion)))) (, ,) (NP (NP (DT the) (NN magnitude)) (PP (IN of) (NP (PRP$ its) (NN speed)))) (, ,) (CC or) (NP (DT both))))) (. .)))
that is to say, the force exerted by one particle on another results in the latter's changing the direction of its motion, the magnitude of its speed, or both.
(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))))))))))) (. .)))