friction vs rays

friction

noun
  • The rubbing of one object or surface against another. 

  • A force that resists the relative motion or tendency to such motion of two bodies in contact. 

  • (Second Sino-Japanese War) Conflict, as between the Communists and non-Hanjian Kuomintang forces. 

  • Conflict, as between persons having dissimilar ideas or interests; clash. 

rays

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