fall off vs roll down

fall off

verb
  • To change the direction of the sail so as to point in a direction that is more down wind; to bring the bow leeward. 

  • To diminish in size, value, etc. 

  • To fall into sin; stray. 

  • To become detached or to drop from. 

roll down

verb
  • Synonym of wind down 

How often have the words fall off and roll down occurred in a corpus of books? (source: Google Ngram Viewer )