prolong vs sustain

prolong

verb
  • To put off to a distant time; to postpone. 

  • To lengthen in time; to extend the duration of 

  • To become longer; lengthen. 

  • To extend in space or length. 

sustain

verb
  • To keep from falling; to bear; to uphold; to support. 

  • To provide for or nourish. 

  • To encourage or sanction (something). 

  • To maintain, or keep in existence. 

  • To allow, accept, or admit (e.g. an objection or motion) as valid. 

  • To confirm, prove, or corroborate; to uphold. 

  • To aid, comfort, or relieve; to vindicate. 

  • To experience or suffer (an injury, etc.). 

noun
  • A mechanism which can be used to hold a note, as the right pedal on a piano. 

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