( Motion ( ( can ( be ( ( described ( as ( ( a change ) ( in position ) ) ) ) ( over ( ( a period ) ( of time ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Motion)) (VP (MD can) (VP (VB be) (VP (VBN described) (PP (IN as) (NP (NP (DT a) (NN change)) (PP (IN in) (NP (NN position))))) (PP (IN over) (NP (NP (DT a) (NN period)) (PP (IN of) (NP (NN time)))))))) (. .)))
Motion can be described as a change in position over a period of time.
(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)))))))) (. .)))