( ( ( The density ) ( of ( a substance ) ) ) ( ( is ( ( the amount ) ( of ( ( ( mass ( -LRB- ( matter -RRB- ) ) ) ( it ( contains ( for ( ( each unit ) ( of ( its volume ) ) ) ) ) ) ) ( -LRB- ( ( amount ( of ( space ( it occupies ) ) ) ) -RRB- ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN density)) (PP (IN of) (NP (DT a) (NN substance)))) (VP (VBZ is) (NP (NP (DT the) (NN amount)) (PP (IN of) (NP (NP (JJ mass) (-LRB- -LRB-) (NN matter) (-RRB- -RRB-)) (SBAR (S (NP (PRP it)) (VP (VBZ contains) (PP (IN for) (NP (NP (DT each) (NN unit)) (PP (IN of) (NP (PRP$ its) (NN volume)))))))) (PRN (-LRB- -LRB-) (NP (NP (NN amount)) (PP (IN of) (NP (NP (NN space)) (SBAR (S (NP (PRP it)) (VP (VBZ occupies))))))) (-RRB- -RRB-)))))) (. .)))
The density of a substance is the amount of mass (matter) it contains for each unit of its volume (amount of space it occupies).
(ROOT (S (NP (NNP Density)) (VP (VBZ describes) (SBAR (WHADJP (WRB how) (JJ much)) (S (NP (NN matter)) (VP (VBZ is) (PP (IN in) (NP (NP (DT a) (JJ certain) (NN amount)) (PP (IN of) (NP (NN space))))))))) (. .)))