For years, the trusty seat belt provided the sole form of passive restraint in our cars. There were debated about their safety, especially relating to children. But over time, mush of the country adopted mandatory seat-belt laws. Statistics have shown that the use of seat belts has saved thousands of lives that might have been lost in collisions.
Air Bags have been under development for many years. The attraction of a soft pillow to land against in a crash must be very strong – the first patent on an inflatable crash-landing device for airplanes was filed during World War II. In the 1980’s the first commercial air bags appeared in automobiles.
Since 1988, all new cars have been required to have air bags on both driver and passenger sides (Light Trucks came under the rule in 1999). To date, Statistics show that air bags reduce the risk of dying in a direct frontal crash by 30 percent. Newer than steering Wheel mounted or Dashboard-mounted bags, but not so widely used, are seat-mounted and door mounted side air-bags. Some experts say that within the nest few years, our cars will go from having dual air bags top having six or even eight air bags. Having evoked some of the controversy that surrounded seat-belt use in its early years, air bags are the subject of serious government and industry research and tests.
Before looking at specifics, let’s review our knowledge of the laws of the motion. First, we know that moving objects have momentum (the product of the mass and velocity of an object. Unless an outside force acts on an object, the object will continue to move its present speed and direction. Cars consist of several objects, including the vehicle itself, Loose objects in the car and, of course, passengers. If these objects are not restrained, they will continue moving at whatever speed the car is traveling at, even if the car is stopped by a collision.
Stopping an object’s momentum requires force acting over a period of time. When a car crashes, the force required to stop an object is very great because the car’s momentum has changed instantly while the passengers’ has not much time to work with. The goal of any supplemental restraint system is to help stop the passenger while doing as little damage to him or her as possible.
What an air bag wants to do is to slow the passengers’ speed to zero with little or no damage. The constraints that it has to work within are huge. The air bag has the space between the passenger and the steering wheel or dashboard and a fraction of a second to work with. Even that tiny amount of space and time is valuable, however, if the system can slow the passenger evenly rather than forcing an abrupt halt to his or her motion.
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