“Air Bags ”
Airbags are yet another device intended on enhancing motoring safety. From 1998 onwards, most new cars sold in Japan and North America, have been required to have airbags on both driver and passenger sides. (Light trucks came under the rule in 1999.) To date, statistics show that airbags reduce the risk of dying in a direct frontal crash by about 30 percent. Then, came seat-mounted and door-mounted side airbags. Today, some cars go far beyond having dual airbags to having six or even eight airbags. Having evoked some of the same controversy that surrounded seat-belt use in its early years, airbags are the subject of serious government and industry research and tests.
The Laws of Motion state that moving objects have momentum (the product of the mass and the velocity of an object). Unless an outside force acts on an object, the object will continue to move at 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 and there is 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 airbag does is to slow the passenger's speed to zero with little or no damage. The constraints that it has to work within are huge. The airbag 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, then it would enhance the needed safety. The airbag system is fitted with a number of devices that make it work as it does; the sensor is the device that tells the bag to inflate. Inflation happens when there is a collision force equal to running into a brick wall at 16 to 24 km per hour. A mechanical switch is flipped when there is a mass shift that closes an electrical contact, telling the sensors that a crash has occurred. The sensors receive information from an accelerometer built into a microchip. The airbag's inflation system reacts sodium azide (NaN3) with potassium nitrate (KNO3)
to produce nitrogen gas. Hot blasts of the nitrogen inflate the airbag.
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