acerbate vs perturb

acerbate

verb
  • To exasperate; to irritate. 

  • To make bitter or sour. 

adj
  • Embittered; having a sour disposition or nature. 

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 acerbate and perturb occurred in a corpus of books? (source: Google Ngram Viewer )