determine which one of the following statements is false: determine which one of the following statements is false: a system's momentum is constant only if a net external force acts on the system for some time. impulse is a vector quantity, where the algebraic sign of the impulse value (positive or negative) indicates the direction of the impulse along a given coordinate axis. changes in momentum are caused by impulses, where an impulse is a net force acting on an object multiplied by the time during which that force interacts with the object. impulses can also be found by determining the area under a plot of force versus time. the concept of an impulse (product of the average net force and the time of interaction) explains the observation that a driver of a car with safety features who crashes to a full stop is likely to leave the scene with minimal injury because a small force is applied over a long time as compared to the driver of a car without those safety features who would experience a large force over a small time. momentum is a vector quantity related to velocity such that if an object is moving it is said to have momentum, with the momentum vector pointing in the same direction as the velocity vector of the object.