People not wearing a seat belt are 30 times more likely to be ejected from a vehicle during a crash. More than 3 out of 4 people who are ejected during a fatal crash die from their injuries. Seat belts saved almost 13, lives in If all drivers and passengers had worn seat belts that year, almost 4, more people would be alive today.
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How does a seatbelt work? Are seatbelts an effective way of preventing injury? Car Safety Systems. Introduction Sitemap. A seatbelt helps to prevent injury in the event of a car crash by reducing the velocity of a body as it experiences a sudden decrease in speed.
Due to the body's inertia , which is its 'resistance to a change in speed or direction of travel', a passenger in a vehicle will want to continue travelling forwards once the car has reached a sudden stop. If the vehicle is travelling at 50mph and crashes into a brick wall, instantly reducing its velocity to zero, the passenger will continue moving forwards at 50mph unless there is something in front of them to create a 'stopping force'. This is because the velocities of the car and passenger are independent.
A seatbelt spreads the stopping force needed to decelerate the passenger across their body. This prevents the body from hitting the windshield or steering column of a car at high speed, which could easily result in injury or death.
It restrains the energy of your shoulders, chest and pelvis when the vehicle is moving. The seat belt is connected to a retractor mechanism, in which a spool allows the seat belt to be rolled out and tightened back as desired. A locking retractor mechanism responds to any kind of strong force or fast movement such as a crash or heavy braking by instantly stopping the spool from rotating and securing your body against sudden forward movement.
Another key element of seat belt technology is the pretensioner, a modification introduced in the s - around the same time as the airbag came into use. An explosive charge is used to drive a concealed piston when sensors detect a sudden stop in vehicle movement.
The piston then drives the spool around which the fabric strap is wrapped. This instant retraction pulls your body firmly back into the seat. Airbags and seat belts are designed to work together, not replace each other. The central element in the retractor is a spool, which is attached to one end of the webbing.
Inside the retractor, a spring applies a rotation force, or torque , to the spool. This works to rotate the spool so it winds up any loose webbing. When you pull the webbing out, the spool rotates counter-clockwise, which turns the attached spring in the same direction. Effectively, the rotating spool works to untwist the spring.
The spring wants to return to its original shape, so it resists this twisting motion. If you release the webbing, the spring will tighten up, rotating the spool clockwise until there is no more slack in the belt. The retractor has a locking mechanism that stops the spool from rotating when the car is involved in a collision. There are two sorts of locking systems in common use today:.
The first sort of system locks the spool when the car rapidly decelerates when it hits something, for example. The diagram below shows the simplest version of this design.
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