A car is stopped for a traffic signal. Assume the car accelerates in the x-direction. The initial momentum is zero. It bounces off with the same speed and angle. A small force acting over a long time can produce a larger impulse than a large force acting over a short time.
Conservation of momentum Consider two interacting objects.
The total momentum of both objects does not change. For this reason we say that the total momentum of the objects is conserved. Newton's third law implies that the total momentum of a system of interacting objects that are not acted on by outside forces is conserved. The total momentum in the universe is conserved. The momentum of a single object, however, changes when a net force acts on the object for a finite time interval.