A passenger's head snaps backward when a car suddenly accelerates forward. This effect illustrates which of Newton's laws?

A passenger's head snaps backward when a car suddenly accelerates forward. This effect illustrates which of Newton's laws?

• A. Newton's First Law of Motion
• B. Newton's Second Law of Motion
• C. Newton's Third Law of Motion
• D. Law of Universal Gravitation

Answer: (A)

The main idea here is inertia—Newton’s first law: an object at rest stays at rest and an object in motion stays in motion unless acted on by a net external force. When the car suddenly speeds up forward, the passenger’s body tends to keep its original motion. The seat provides the forward force to accelerate the torso, but the head, due to inertia, doesn’t instantly share that change and lags behind relative to the car. That lag makes the head snap backward in the car’s frame. The situation highlights inertia in action: motion changes require a force, and the head’s resistance to change in motion creates the momentary backward snap. The second law is involved in how the force from the seat produces acceleration, but the observable effect is best understood through inertia. The other laws don’t explain this specific behavior.

The main idea here is inertia—Newton’s first law: an object at rest stays at rest and an object in motion stays in motion unless acted on by a net external force. When the car suddenly speeds up forward, the passenger’s body tends to keep its original motion. The seat provides the forward force to accelerate the torso, but the head, due to inertia, doesn’t instantly share that change and lags behind relative to the car. That lag makes the head snap backward in the car’s frame. The situation highlights inertia in action: motion changes require a force, and the head’s resistance to change in motion creates the momentary backward snap. The second law is involved in how the force from the seat produces acceleration, but the observable effect is best understood through inertia. The other laws don’t explain this specific behavior.