( ( ( ( An object ) ( at rest ) ) ( remains ( at rest ) ) ) ( , ( ( ( an object ) ( in motion ) ) ( ( ( remains ( in motion ) ) ( when ( there ( is ( ( no force ) ( acting ( upon it ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (S (NP (NP (DT An) (NN object)) (PP (IN at) (NP (NN rest)))) (VP (VBZ remains) (PP (IN at) (NP (NN rest))))) (, ,) (NP (NP (DT an) (NN object)) (PP (IN in) (NP (NN motion)))) (VP (VBZ remains) (PP (IN in) (NP (NN motion))) (SBAR (WHADVP (WRB when)) (S (NP (EX there)) (VP (VBZ is) (NP (NP (DT no) (NN force)) (VP (VBG acting) (PP (IN upon) (NP (PRP it))))))))) (. .)))
An object at rest remains at rest, an object in motion remains in motion when there is no force acting upon it.
(ROOT (S (SBAR (IN If) (S (NP (DT no) (JJ unbalanced) (NN force)) (VP (VBZ acts) (PP (IN on) (NP (DT an) (NN object)))))) (NP (DT the) (NN object)) (VP (VBZ remains) (PP (PP (IN at) (NP (JJ constant) (NN velocity))) (CC or) (PP (IN at) (NP (NN rest))))) (. .)))