American mother, unmet, made up driving force (8)

I believe the answer is:

momentum

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'driving force' is the definition.
(impetus or force of a moving object)

'american mother unmet made up' is the wordplay.
'american mother' becomes 'mom' (mom is a kind of mother. I am not sure about the 'american' bit.).
'made up' is an anagram indicator.
'unmet' is an anagram of 'entum'.
'mom'+'entum'='MOMENTUM'

Can you help me to learn more?

(Other definitions for momentum that I've seen before include "Corbynites" , "driving power" , "Drive" , "Forward impetus" , "Impetus from motion" .)

I've seen this clue in the Sydney Morning Herald.

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