( ( Since ( velocity ( is ( defined ( as ( ( the rate ) ( ( at which ) ( ( the position ) changes ) ) ) ) ) ) ) ) ( , ( ( this motion ) ( ( results ( in ( zero velocity ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN Since) (S (NP (NN velocity)) (VP (VBZ is) (VP (VBN defined) (PP (IN as) (NP (NP (DT the) (NN rate)) (SBAR (WHPP (IN at) (WHNP (WDT which))) (S (NP (DT the) (NN position)) (VP (VBZ changes)))))))))) (, ,) (NP (DT this) (NN motion)) (VP (VBZ results) (PP (IN in) (NP (CD zero) (NN velocity)))) (. .)))
Since velocity is defined as the rate at which the position changes, this motion results in zero velocity.
(ROOT (S (NP (NNP Motion)) (VP (MD can) (VP (VB be) (VP (VBN defined) (ADVP (RB simply)) (PP (IN as) (NP (NP (DT a) (NN change)) (PP (IN in) (NP (NN position)))))))) (. .)))