A student comes up to you after class, excited to show you that they have found a violation in the law of conservation of momentum. They show you a video that they took of two identical toy cars that use a spring to move them forward. It is clear both cars are moving at the same velocity as they collide into each other, stick together, and come to a complete stop without moving after colliding. Is this truly a violation of the law of conservation of momentum? If not, how do you explain to the student that momentum is still conserved in this system?