( ( ( ( ( The object ) ( exerts ( ( a force ) ( on ( the spring ) ) ) ) ) and ) ( ( the spring ) ( exerts ( ( a force ) ( on ( the object ) ) ) ) ) ) . )
(ROOT (S (S (NP (DT The) (NN object)) (VP (VBZ exerts) (NP (NP (DT a) (NN force)) (PP (IN on) (NP (DT the) (NN spring)))))) (CC and) (S (NP (DT the) (NN spring)) (VP (VBZ exerts) (NP (NP (DT a) (NN force)) (PP (IN on) (NP (DT the) (NN object)))))) (. .)))
The object exerts a force on the spring and the spring exerts a force on the object.
(ROOT (S (NP (JJ Bouyant) (NN force)) (VP (VBZ is) (NP (NP (DT the) (JJ upward) (NN force)) (VP (VBN exerted) (PP (IN by) (NP (NP (NNS fluids)) (SBAR (WHADVP (WRB when)) (S (NP (NP (DT any) (NN object)) (, ,) (PP (JJ such) (IN as) (NP (DT a) (NN boat))) (, ,)) (VP (VBZ is) (VP (VBN placed) (PP (IN in) (NP (PRP it)))))))))))) (. .)))