( ( ( ( ( ( The ( time interval ) ) ( ( required ( for ( the wave ) ) ) ( to ( travel ( exactly ( one wavelength ) ) ) ) ) ) , ) ( that ( ( is ( for ( ( the displacement ) ( at ( point r4 ) ) ) ) ) ( to ( ( return ( to ( the ( same value ) ) ) ) ( as ( it ( had ( at ( ( the beginning ) ( of ( that ( time interval ) ) ) ) ) ) ) ) ) ) ) ) ) , ) ( ( ( is ( known ( as ( the period ) ) ) ) and ) ( is ( ( given ( the symbol ) ) T. ) ) ) )
(ROOT (S (NP (NP (DT The) (NN time) (NN interval)) (VP (VBN required) (PP (IN for) (NP (DT the) (NN wave))) (S (VP (TO to) (VP (VB travel) (NP (RB exactly) (CD one) (NN wavelength)))))) (, ,) (SBAR (WHNP (WDT that)) (S (VP (VBZ is) (PP (IN for) (NP (NP (DT the) (NN displacement)) (PP (IN at) (NP (NN point) (NNS r4))))) (S (VP (TO to) (VP (VB return) (PP (TO to) (NP (DT the) (JJ same) (NN value))) (SBAR (IN as) (S (NP (PRP it)) (VP (VBD had) (PP (IN at) (NP (NP (DT the) (NN beginning)) (PP (IN of) (NP (DT that) (NN time) (NN interval)))))))))))))) (, ,)) (VP (VP (VBZ is) (VP (VBN known) (PP (IN as) (NP (DT the) (NN period))))) (CC and) (VP (VBZ is) (VP (VBN given) (NP (DT the) (NN symbol)) (NP (NNP T.)))))))
The time interval required for the wave to travel exactly one wavelength, that is for the displacement at point r4 to return to the same value as it had at the beginning of that time interval, is known as the period and is given the symbol T.
(ROOT (S (NP (NN Period)) (VP (VBZ is) (NP (NP (DT the) (NN time) (NN interval)) (VP (VBN required) (PP (IN for) (NP (CD one) (JJ complete) (NN wave) (S (VP (TO to) (VP (VB pass) (NP (NP (DT a) (NN point)) (VP (VBN called))))))))))) (. .)))