It’s more of a fundamental principle of mechanics. It’s not self-evident. It is empirically derived, and subject to revision.

Apparently there are no axioms within physics like there are in mathematics:
-a number is equal to itself
-transitive law. a=b, b=c, then a=c
-axiom of empty set

Axioms are accepted as true without proof. They’re not necessarily absolute truths, universal, or immutable and may only apply within a given context.

Disclaimer: I summarized the above after using 2 different LLMs.