Final answer:
The 'snap back' effect when a car is struck from behind is an example of Newton's First Law of Motion, or the Law of Inertia, where a person's head initially remains at rest while the body moves forward until the neck provides the force to move the head.
Step-by-step explanation:
The scenario where a person's head appears to "snap back" when sitting in a car struck from behind emphasizes Newton's First Law of Motion, also known as the Law of Inertia. According to Newton's first law, an object at rest will stay at rest, and an object in motion will stay in motion at a constant velocity unless acted upon by a net external force. In the case of the car being struck from behind, the car suddenly accelerates forward due to the impact, but the person's head tends to remain in its original state of rest relative to the car (due to inertia). As the body is pushed forward by the car seat, the head lags briefly, creating the "snap back" effect, before also moving forward due to the force transmitted through the neck and body.