( ( The balloon ) ( ( exerts ( ( an ( upward force ) ) ( of ( ( 92.8 N ) ( on ( the payload ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NN balloon)) (VP (VBZ exerts) (NP (NP (DT an) (JJ upward) (NN force)) (PP (IN of) (NP (NP (CD 92.8) (NNS N)) (PP (IN on) (NP (DT the) (NN payload))))))) (. .)))
The balloon  exerts an upward force of 92.8 N on the payload.
(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)))))))))))) (. .)))