center of gravity vs midpoint

center of gravity and midpoint both are nouns.

Word	Noun	Adjective	Verb	Adverb
center of gravity	Yes	No	No	No
midpoint	Yes	No	No	No

As nouns, midpoint is a hypernym of center of gravity; that is, midpoint is a word with a broader meaning than center of gravity:

center of gravity: the point within something at which gravity can be considered to act; in uniform gravity it is equal to the center of mass
midpoint: a point equidistant from the ends of a line or the extremities of a figure

Other hypernyms of center of gravity include center, centre.

center of gravity (noun)	midpoint (noun)
the point within something at which gravity can be considered to act; in uniform gravity it is equal to the center of mass	a point equidistant from the ends of a line or the extremities of a figure