Inertia explains why objects in motion tend to do what when a vehicle stops?

• A. Move backward when the vehicle stops
• B. Stay in place unless forced to move
• C. Continue moving forward when the vehicle stops unless restrained
• D. Accelerate due to gravity

Answer: (C)

Inertia is the tendency of an object to keep doing what it’s doing—moving at the same speed and direction unless a net external force acts on it. When a vehicle stops, the car itself is brought to rest by braking, but anything not secured inside doesn’t instantly feel that stopping force. It keeps moving forward at the car’s prior speed, so relative to the stopped car it appears to lurch forward. A seat belt or other restraint provides the external force needed to bring you to rest with the car. Gravity isn’t involved in this horizontal stopping behavior, so it doesn’t cause acceleration here.