WordNet records no synonym and no antonym for conservation of momentum. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
the principle that the total linear momentum in a closed system is constant and is not affected by processes occurring inside the system
Synonyms, antonyms and the broader and narrower relations for conservation of momentum come from Princeton University’s WordNet. Full sources and licences.