( Gravity ( ( exerts ( ( ( ( a force ) downward ) , ) ( ( elevator floor ) upward ) ) ) . ) )
(ROOT (S (NP (NNP Gravity)) (VP (VBZ exerts) (S (S (NP (DT a) (NN force)) (ADVP (RB downward))) (, ,) (S (NP (NN elevator) (NN floor)) (ADVP (RB upward))))) (. .)))
Gravity exerts a force downward, elevator floor upward.
(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)))))))))))) (. .)))