encourage vs perturb

encourage

verb
  • To foster, give help or patronage 

  • To mentally support; to motivate, give courage, hope or spirit. 

  • To spur on, strongly recommend. 

perturb

verb
  • To disturb; to bother or unsettle. 

  • To modify the motion of a body by exerting a gravitational force. 

  • To modify slightly, such as an equation or value. 

  • To slightly modify the motion of an object. 

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