Non-Stretching Seatbelt

The task of the seatbelt is to stop you with the car so that your stopping distance is probably 4 or 5 times greater than if you had no seatbelt. A crash which stops the car and driver must take away all its kinetic energy, and the work-energy principle then dictates that a longer stopping distance decreases the impact force. For the example car crash scenario the stopping distance is one foot, the force on a 160 lb driver is about 4800 lb or 2.4 tons, and the deceleration about 30 g's. A moderate amount of stretch in the seatbelts will reduce the average impact force. 安全带的任务是让你与汽车一起停止，使得你的停止距离可能比没有安全带时大4到5倍。一次碰撞事故必须使汽车和驾驶员停止，这将带走所有动能，根据功-能原理，较长的停止距离会减小冲击力。在所描述的汽车碰撞场景中，停止距离为一英尺，160磅的驾驶员所受的力约为4800磅或2.4吨，减速度约为30个重力加速度。安全带的适度伸长将减少平均冲击力。 Seatbelt variations 安全带变种

Stretching Seatbelt

A moderate amount of stretch in a seatbelt harness can extend the stopping distance and reduce the average impact force on the driver compared to a non-stretching harness. If the belt stretched 0.5 ft in the example car crash scenario, it would reduce the deceleration to 20 g's and the average impact force to 3200 lb compared to 30 g's and 4800 lb for a non-stretching seatbelt. Either a stretching or non-stretching seat belt reduces the impact force compared to no seatbelt. 安全带适度伸长可以延长停车距离，从而相比不伸长的安全带减少驾驶员的平均冲击力。在示例的汽车碰撞场景中，如果安全带伸长0.5英尺，它将使减速度降低到20g，平均冲击力降低到3200磅，相比不伸长的安全带的30g和4800磅。无论是伸长还是不伸长的安全带，相比没有安全带，都能减少冲击力。 Seatbelt variations 安全带变种

No Seatbelt!

With no seatbelt to stop the driver with the car, the driver flies free until stopped suddenly by impact on the steering column, windshield, etc. The stopping distance is estimated to be about one fifth of that with a seatbelt, causing the average impact force to be about five times as great. The work done to stop the driver is equal to the average impact force on the driver times the distance traveled in stopping. A crash which stops the car and driver must take away all its kinetic energy, and the work-energy principle then dictates that a shorter stopping distance increases the impact force.

Warning! This is stated in terms of the driver, but any person in the vehicle who is not constrained by a seatbelt is subject to these extreme dangers. A seatbelt stops you with the car, which is almost always a much larger stopping distance than your stopping distance when you are flying free and collide with something. Riding in the back of a pickup truck or holding onto a car in any way takes away the protection of a seatbelt and airbag. Since the force to stop your body in even a low speed collision is in the range of tons, there is no way you can hold on and prevent injury. A shorter stopping distance always means a greater impact force on you. No exceptions - it's the law (physical law, that is)!

How far will the driver fly while the car is stopping?

When would you be better off not wearing your seatbelt?

Example car crash scenario

With no seatbelt to stop the driver with the car, the driver flies free until stopped suddenly by impact on the steering column, windshield, etc. If the distance to impact is greater than 2 ft, the car will be at rest or even bouncing back when the driver strikes it at 30 miles/hr.

When would you be better off not wearing your seatbelt?

Example car crash scenario