( ( Thermal mass ) ( ( ( stores heat ) ( by ( changing ( its temperature ) ) ) ) . ) )
(ROOT (S (NP (JJ Thermal) (NN mass)) (VP (VBZ stores) (NP (NN heat)) (PP (IN by) (S (VP (VBG changing) (NP (PRP$ its) (NN temperature)))))) (. .)))
Thermal mass stores heat by changing its temperature.
(ROOT (S (NP (DT The) (NN term) (JJ thermal) (NN expansion)) (VP (VBZ is) (VP (VBN used) (S (VP (TO to) (VP (VB describe) (NP (NP (DT the) (NN change)) (PP (IN in) (NP (NN size) (CC or) (NN volume))) (PP (IN of) (NP (NP (DT a) (VBN given) (NN mass)) (PP (IN with) (NP (NN temperature))))))))))) (. .)))