fluidity vs rigidity

fluidity

noun
  • A measure of the extent to which something is fluid. The reciprocal of its viscosity. 

  • The quality of being fluid or free-flowing 

  • The state of being fluid rather than viscous 

rigidity

noun
  • stickiness (of prices/wages etc.). Describing the tendency of prices and money wages to adjust to changes in the economy with a certain delay. 

  • The quality or state of being rigid; lack of pliability; the quality of resisting change of physical shape 

  • Stiffness of appearance or manner; want of ease or elegance. 

  • The amount of resistance with which a body opposes change of form. 

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