( Density ( ( can ( be ( explained ( as ( ( ( the amount ) ( of ( matter ( in ( ( an object ) ( -LRB- ( mass -RRB- ) ) ) ) ) ) ) ( ( has ( per ( ( unit or ) space ) ) ) ( occupied ( by ( ( the matter ) ( -LRB- ( volume -RRB- ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Density)) (VP (MD can) (VP (VB be) (VP (VBN explained) (SBAR (IN as) (S (NP (NP (DT the) (NN amount)) (PP (IN of) (NP (NP (NN matter)) (PP (IN in) (NP (NP (DT an) (NN object)) (PRN (-LRB- -LRB-) (NP (NN mass)) (-RRB- -RRB-))))))) (VP (VBZ has) (PP (IN per) (NP (NN unit) (CC or) (NN space))) (VP (VBD occupied) (PP (IN by) (NP (NP (DT the) (NN matter)) (PRN (-LRB- -LRB-) (NN volume) (-RRB- -RRB-))))))))))) (. .)))
Density can be explained as the amount of matter in an object (mass) has          per unit or space occupied by the matter (volume).
(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))))))))) (. .)))