cool off vs loosen up

cool off

verb
  • To decrease in temperature, activity, or temper. 

  • To cause to decrease in temperature, activity or temper. 

loosen up

verb
  • To become loose; to loosen; to relax (a muscle, etc.). 

  • To relax; to act less seriously. 

How often have the words cool off and loosen up occurred in a corpus of books? (source: Google Ngram Viewer )