discouragement vs impetus

discouragement

noun
  • Anything that discourages. 

  • The act of discouraging. 

  • The loss of confidence or enthusiasm. 

impetus

noun
  • Anything that impels; a stimulating factor. 

  • The force or energy associated with a moving body; a stimulus. 

  • An activity in response to a stimulus. 

  • A force, either internal or external, that impels; an impulse. 

  • A principle of motive force, held as exquivalent to weight times velocity by John Buridan, in an auxiliary theory of Aristotelian dynamics introduced by John Philoponus, describing projectile motion against gravity as linear until it transitions to a vertical drop and the intellectual precursor to the concepts of inertia, momentum and acceleration in classical mechanics. 

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