This paper isolates physical momentum exchange as a candidate admissibility condition for physical reality and evaluates it under a strict elimination-by-necessity framework. Momentum exchange is examined solely as a physically enforcing mechanism acting through reciprocal back-reaction and local interaction in spacetime, independent of mathematical bookkeeping, conservation descriptions, or interpretive constructs. By removing non-enforcing representations while retaining all physically enforcing interactions, the analysis determines whether momentum exchange is necessary and whether it is sufficient for physical reality. The paper shows that momentum exchange enforces physical change but cannot operate independently of force and energy exchange, establishing momentum exchange as necessary but not sufficient within a closed, mechanism-only logical structure.