inactivity vs inertia

inactivity and inertia both are nouns.

Word	Noun	Adjective	Verb	Adverb
inactivity	Yes	No	No	No
inertia	Yes	No	No	No

As nouns, inactivity and inertia are synonyms defined as:

Other synonyms of inactivity include inactiveness.

inactivity (noun)	inertia (noun)
being inactive; being less active	a disposition to remain inactive or inert
a disposition to remain inactive or inert	(physics) the tendency of a body to maintain its state of rest or uniform motion unless acted upon by an external force
the state of being inactive