Force Morgan to become diver (7)
I believe the answer is:
frogman
'diver' is the definition.
(synonyms)
'force morgan to become' is the wordplay.
'force' becomes 'F' (symbol used in Physics e.g. f=ma).
'to become' indicates an anagram.
'morgan' anagrammed gives 'rogman'.
'f'+'rogman'='FROGMAN'
(Other definitions for frogman that I've seen before include "Person who works underwater using a portable air supply" , "Swimmer working underwater" , "Male diver" , "Underwater swimmer with breathing apparatus" , "Underwater diver" .)