Final answer:
This situation is an example of Newton's First Law of Motion, demonstrating the tendency of objects to remain at constant velocity unless an external force is applied.
Step-by-step explanation:
The scenario described, where stuff on your seat flies forward when you hit the brakes, is an example of Newton's First Law of Motion. This law, sometimes called the law of inertia, states that every object will continue to be in a state of rest, or move at a constant speed in a straight line unless it is compelled to change by an outside force. In this case, when the car was braking, an external force was applied to the car, but not to the loose objects inside. As a result, the objects continued moving at the previous speed of the car until another force (such as the floor of the car or another object) stops them.