terra firma vs physical object

terra firma and physical object both are nouns.

Word	Noun	Adjective	Verb	Adverb
terra firma	Yes	No	No	No
physical object	Yes	No	No	No

As nouns, physical object is a hypernym of terra firma; that is, physical object is a word with a broader meaning than terra firma:

terra firma: the solid part of the earth's surface
physical object: a tangible and visible entity; an entity that can cast a shadow

Other hypernyms of terra firma include object.

terra firma (noun)	physical object (noun)
the solid part of the earth's surface	a tangible and visible entity; an entity that can cast a shadow