inertia vs inactivity

inertia and inactivity both are nouns.

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

As nouns, inertia and inactivity are synonyms defined as:

Other synonyms of inertia include inactiveness.

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