Newton was to emerge to get into motion (8)
I believe the answer is:
geometer
'newton was' is the definition.
(Isaac Newton studied geometry)
'to emerge to get into motion' is the wordplay.
'to get into motion' indicates anagramming the letters (letters move around).
'to'+'emerge'='toemerge'
'toemerge' is an anagram of 'GEOMETER'.
(Other definitions for geometer that I've seen before include "One as Euclid, Riemann" , "Type of mathematician" , "Scientist" , "One skilled in a branch of mathematics" .)