If there is a properly adjusted headrest, the head will be moved forward at the same time and rate as the torso, meaning that the neck does not have to bend uncomfortably. This happens because if a mass (the head) is stationary, Newton's First Law states that it will stay this way until it is acted upon by an unbalanced force. If a passenger is wearing a seatbelt, their torso is moved rapidly forward with the car, leaving their head behind and making it bend backwards quickly enough to cause injury. If improperly adjusted, they cannot provide adequate support and stop injury (usually whiplash, which is an injury related to sudden distortion of the neck).įor example, if a car is stationary and it is acted upon by an unbalanced force in a rear impact, it would move quickly forward. Headrests extend above the seat of a car and can be adjusted to properly fit the driver or passenger. The diagram above shows the effect of a collision on a body without the aid of a properly adjusted headrest. A lot of force would still be applied from the seatbelt to the body frame, but it keeps the body in place and stops a collision with hard objects like the steering wheel and objects that could cut, like the windscreen. When wearing a seat belt, the passenger is part of a car, meaning that they too would come to a halt- or, if they did travel, they would only go a short distance and collide with the seat belt strap instead of a glass windshield.
If the car came to an abrupt halt after travelling at constant velocity (for example, in a motor vehicle accident) and the passenger was not wearing a seatbelt, they would continue travelling at constant velocity, probably resulting in a collision with the windscreen or the back of the seat in front of them. Were it not for seatbelts, your body would be acted upon by Newton's First Law independently of the vehicle. Seat belts attach your body mass to that of a car, meaning that when the car accelerates or decelerates, you do also. Modern seatbelts are anchored using a three-point system, as demonstrated in the diagram above- two points are attached to the floor (one on either side of the seat), and the other comes across the body to attach to the ceiling.
Seat Belts are the primary means of injury prevention in all motor accidents, big or small.
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