dip into vs swot up on

dip into

verb
  • To read, examine or engage in (something) in a cursory or casual manner. 

  • To spend some of a source of money (such as one's savings). 

  • Used other than figuratively or idiomatically: dip into. 

swot up on

verb
  • To study particularly hard to learn a subject quickly. 

How often have the words dip into and swot up on occurred in a corpus of books? (source: Google Ngram Viewer )