inactiveness vs inertia

inactiveness and inertia both are nouns.

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

As nouns, inactiveness and inertia are synonyms defined as:

Other synonyms of inactiveness include inactivity.

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