( ( If ( ( ( the acceleration ) ( acting ( on ( a body ) ) ) ) ( is ( that ( due ( to gravity ) ) ) ) ) ) ( , ( ( ( the force ) ( acting ( on it ) ) ) ( ( is ( ( ( the force ) ( of gravity ) ) ( which ( we ( call weight ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN If) (S (NP (NP (DT the) (NN acceleration)) (VP (VBG acting) (PP (IN on) (NP (DT a) (NN body))))) (VP (VBZ is) (ADJP (RB that) (JJ due) (PP (TO to) (NP (NN gravity))))))) (, ,) (NP (NP (DT the) (NN force)) (VP (VBG acting) (PP (IN on) (NP (PRP it))))) (VP (VBZ is) (NP (NP (DT the) (NN force)) (PP (IN of) (NP (NN gravity))) (SBAR (WHNP (WDT which)) (S (NP (PRP we)) (VP (VBP call) (NP (NN weight))))))) (. .)))
If the acceleration acting on a body is that due to gravity, the force acting on it is the force of gravity which we call weight .
(ROOT (S (NP (NNP Weight)) (VP (VBZ is) (NP (NP (DT the) (NN force)) (PP (IN of) (NP (NN gravity))))) (. .)))