Newton’s law of inertia is illustrated in tests with crash dummies, seat belts, and airbags, wherein the object stays in motion unless there is an unbalanced force applied to it.
Inertia is the main reason why there are seatbelts and airbags in the car. In this case, when the seatbelt is trapped to the passenger, the passenger experiences the same state of motion as the car. If the car accelerates/decelerates, the passenger experiences it too. When the car experiences collision, an unbalance force is acted upon it. This causes the car to stop abruptly, and the passenger shares the same state of motion because of the seatbelt and the airbags that apply the unbalanced force to stop the passenger to go forward.
