( ( For ( this reason ) ) ( , ( ( ( kinetic energy ) ( of molecules ) ) ( ( is ( called ( thermal energy ) ) ) . ) ) ) )
(ROOT (S (PP (IN For) (NP (DT this) (NN reason))) (, ,) (NP (NP (JJ kinetic) (NN energy)) (PP (IN of) (NP (NNS molecules)))) (VP (VBZ is) (VP (VBN called) (NP (JJ thermal) (NN energy)))) (. .)))
For this reason, kinetic energy of molecules is called thermal energy.
(ROOT (S (NP (NP (DT The) (NN sum)) (PP (IN of) (NP (NP (DT the) (JJ kinetic) (CC and) (JJ potential) (NNS energies)) (PP (IN of) (NP (NP (DT a) (NN system) (POS 's)) (NNS atoms) (CC and) (NNS molecules)))))) (VP (VBZ is) (VP (VBN called) (NP (JJ internal) (NN energy)))) (. .)))