Final answer:
The change in velocity is the most significant variable when calculating changes in linear momentum, especially for a constant-mass system where the mass remains unchanged.
Step-by-step explanation:
When calculating changes in linear momentum, the variable that plays the largest role is the change in velocity of the system. According to Essential Knowledge 4.B.1, the change in linear momentum for a constant-mass system is the product of the system's mass and the change in velocity of the center of mass.
The linear momentum, p, of a system is defined as p = mv, where m is the mass of the system and v is its velocity. Hence, for a constant mass system, any change in momentum (Δp) would primarily come from a change in velocity (Δv), since mass (m) remains constant.
Momentum is conserved in the absence of external forces or within a closed system where all forces are internal. However, when external forces act on a system, they can produce large changes in the momentum of the system, highlighting velocity's role in altering a system's momentum.