rubbing vs grinding

rubbing and grinding both are nouns.

Word	Noun	Adjective	Verb	Adverb
rubbing	Yes	No	No	No
grinding	Yes	No	No	No

As nouns, grinding is a hyponym of rubbing; that is, grinding is a word with a more specific, narrower meaning than rubbing:

rubbing: the resistance encountered when one body is moved in contact with another
grinding: the wearing down of rock particles by friction due to water or wind or ice

Other hyponyms of rubbing include abrasion, attrition, detrition, adhesive friction, grip, traction.

rubbing (noun)	grinding (noun)
effort expended in moving one object over another with pressure	a harsh and strident sound (as of the grinding of gears)
representation consisting of a copy (as of an engraving) made by laying paper over something and rubbing it with charcoal	material resulting from the process of grinding
the resistance encountered when one body is moved in contact with another	the wearing down of rock particles by friction due to water or wind or ice