Final answer:
The statement is true; a net force changes an object's momentum when applied over a time interval, as indicated by the impulse-momentum theorem and Newton's second law expressed in terms of momentum.
Step-by-step explanation:
The statement 'A net force changes momentum when applied over a time interval' is true. This concept can be framed using Newton's second law of motion in terms of momentum, which tells us that the net external force (Fnet) equals the change in momentum of a system (Δp) divided by the time (Δt) over which it changes. Hence, it is formulated as Fnet = Δp / Δt.
In more practical terms, this means that when you apply a force to an object for a certain amount of time, you impart an impulse to the object, which is equal to the product of the force and the time interval. This impulse is responsible for changing the object's momentum. Consequently, a net force will indeed change an object's momentum, as long as it acts over a period of time. The effect of the force manifests a change in either the speed or direction of the object, or both, depending on the specifics of the force applied.