( ( Internal energy ) ( ( is ( ( ( ( ( the sum ) ( of ( ( the ( potential energy ) ) ( of ( a system ) ) ) ) ) , ) and ) ( ( the ( kinetic energy ) ) ( of ( the system ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Internal) (NN energy)) (VP (VBZ is) (NP (NP (NP (DT the) (NN sum)) (PP (IN of) (NP (NP (DT the) (JJ potential) (NN energy)) (PP (IN of) (NP (DT a) (NN system)))))) (, ,) (CC and) (NP (NP (DT the) (JJ kinetic) (NN energy)) (PP (IN of) (NP (DT the) (NN system)))))) (. .)))
Internal energy is the sum of the potential energy of a system, and the kinetic energy of the system.
(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)))) (. .)))