Which mechanism explains why seat belts keep you from moving forward during a crash?

• A. Inertia
• B. Gravity
• C. Drag
• D. Momentum

Answer: (A)

Inertia—the tendency of a moving object to resist changes in its motion. During a crash, the car decelerates very quickly, but your body tends to keep moving at the car’s previous speed. The seat belt provides a restraining force that acts on you, causing your body to decelerate with the car instead of continuing forward. By applying this opposing force, the belt changes your motion along with the vehicle, reducing the forward fling and the risk of injury. The belt also spreads the stopping force over time and across your body, which helps manage the deceleration more safely. Gravity and drag aren’t what primarily stop forward motion in a crash, and momentum is the quantity being changed by the belt’s force, not the mechanism itself.