inertia vs inertness

inertia

noun
  • In a person, unwillingness to take action. 

  • Lack of activity; sluggishness; said especially of the uterus, when, in labour, its contractions have nearly or wholly ceased. 

  • The property of a body that resists any change to its uniform motion; equivalent to its mass. 

inertness

noun
  • Lack of activity or exertion; habitual indisposition to action or motion 

  • Absence of the power of self-motion; inertia. 

  • Quality of being unreactive with other chemical compounds or elements. 

How often have the words inertia and inertness occurred in a corpus of books? (source: Google Ngram Viewer )