( ( ( ( ( ( ( Mass ( on ( the ( other hand ) ) ) ) ( is ( what ( would ( be ( ( ( measured ( using ( a ( comparative balance ) ) ) ) , ) ( by ( ( hanging ( two objects ) ) ( on ( ( the ends ) ( of ( a beam ) ) ) ) ) ) ) ) ) ) ) ) , ) and ) then ) ( ( ( seeing ( by ( ( how much ) ( ( one side ) ( is ( pulled down ) ) ) ) ) ) . ) ( Masses ( are ( measured ( by ( comparing ( ( an ( unknown mass ) ) ( against ( a ( known one ) ) ) ) ) ) ) ) ) ) ) . )
(ROOT (S (S (NP (NP (NNP Mass)) (PP (IN on) (NP (DT the) (JJ other) (NN hand)))) (VP (VBZ is) (SBAR (WHNP (WP what)) (S (VP (MD would) (VP (VB be) (VP (VBN measured) (S (VP (VBG using) (NP (DT a) (JJ comparative) (NN balance)))) (, ,) (PP (IN by) (S (VP (VBG hanging) (NP (CD two) (NNS objects)) (PP (IN on) (NP (NP (DT the) (NNS ends)) (PP (IN of) (NP (DT a) (NN beam))))))))))))))) (, ,) (CC and) (RB then) (S (INTJ (UH seeing) (PP (IN by) (SBAR (WHADJP (WRB how) (JJ much)) (S (NP (CD one) (NN side)) (VP (VBZ is) (VP (VBN pulled) (PRT (RP down))))))) (. .)) (NP (NNP Masses)) (VP (VBP are) (VP (VBN measured) (PP (IN by) (S (VP (VBG comparing) (NP (NP (DT an) (JJ unknown) (NN mass)) (PP (IN against) (NP (DT a) (VBN known) (NN one)))))))))) (. .)))
Mass on the other hand is what would be measured using a comparative balance, by hanging two objects on the ends of a beam, and then seeing by how much one side is pulled down. Masses are measured by comparing an unknown mass against a known one.
(ROOT (S (NP (DT A) (NN student)) (VP (MD should) (VP (VB use) (NP (DT a) (NN balance) (S (VP (TO to) (VP (VB compare) (NP (NP (DT the) (NNS masses)) (PP (IN of) (NP (CD two) (JJ small) (NNS rocks)))))))))) (. .)))