( However ( , ( ( to ( ( accelerate ( the barbell ) ) upward ) ) ( , ( ( the person ) ( ( must ( ( exert ( an ( upward force ) ) ) ( on ( the barbell ) ) ) ) . ) ) ) ) ) )
(ROOT (S (ADVP (RB However)) (, ,) (S (VP (TO to) (VP (VB accelerate) (NP (DT the) (NN barbell)) (ADVP (RB upward))))) (, ,) (NP (DT the) (NN person)) (VP (MD must) (VP (VB exert) (NP (DT an) (JJ upward) (NN force)) (PP (IN on) (NP (DT the) (NN barbell))))) (. .)))
However, to accelerate the barbell upward, the person must exert an upward force on the barbell.
(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)))))))))))) (. .)))