activate vs knock off

activate

verb
  • To put a device, mechanism (alarm etc.) or system into action or motion; to trigger, to actuate, to set off, to enable. 

  • To organize or create a military unit or station. 

  • To bring a player back after an injury. 

  • To render a substance radioactive. 

  • To hasten a chemical reaction, especially by heating. 

  • To render more reactive; excite. 

  • To remove the limitations of demoware by providing a license; to unlock. 

  • To render a molecule reactive, active, or effective in performing its function. 

  • To encourage development or induce increased activity; to stimulate. 

  • To aerate in order to aid decomposition of organic matter. 

knock off

verb
  • To halt one's work or other activity. 

  • To rob. 

  • To defeat. 

  • To have sex with. 

  • To remove, as a discount or estimate. 

  • To make a copy of, as of a design. 

  • To assign (an item) to a bidder at an auction, indicated by knocking on the counter. 

  • To remove by hitting (something, someone) 

  • To kill. 

  • To accomplish hastily. 

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