Which would have the greater the effect on the momentum, changing the mass or changing the velocity?

Momentum is given by the formula \( p = mv \), where \( p \) is momentum, \( m \) is mass, and \( v \) is velocity.

From this formula, it's clear that both mass and velocity contribute to momentum. However, the effect of changing mass versus changing velocity on momentum can vary greatly depending on the specific changes made.

1. Changing Mass: If you change the mass of an object, the momentum will also change linearly with the mass (if velocity remains constant). For example, if you double the mass, the momentum doubles.

2. Changing Velocity: If you change the velocity of the object while keeping mass constant, the momentum will change linearly with velocity. For instance, if you double the velocity, the momentum also doubles.

However, since momentum is a product of both mass and velocity, changing velocity typically has a more pronounced effect on the momentum because velocity can be altered more drastically in many situations (e.g., by accelerating an object) compared to mass, which usually changes less frequently or involves more effort (like adding or removing mass).

In conclusion, while both mass and velocity affect momentum, changing velocity often has a greater practical effect on momentum in many scenarios.

So, the answer would be: Velocity.