heaviness vs inertia

heaviness

noun
  • The state of being heavy; weight, weightiness, force of impact or gravity. 

inertia

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

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

  • In a person, unwillingness to take action. 

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