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Your car’s airbag is more than a pillow of protection that may prevent harm during an accident. It is designed to inflate to exactly the right pressure at exactly the right moment -- otherwise, it can't slow down and spread out a person's impact during the crash. To do all this, an airbag relies on the pressure exerted by a gas. Random Gases, Predictable Result In a gas, molecules fly around in random directions. When they hit something -- like the interior of an airbag -- they push against it a little bit before bouncing off and flying in another direction. The amount of pressure the gas exerts on the inside of the bag depends on how much is in there and how hot it is. Lots of hot gas will exert more pressure than a little bit of cool gas. Of course, the size of the airbag plays a part, too -- it takes more pressure to inflate a bigger bag. The gas that does all this work in an airbag is nitrogen. Inside an airbag is a pellet of material called sodium azide, which is made of sodium and nitrogen. Under ordinary conditions, sodium azide is stable but toxic. But if you expose it to high temperatures -- like from an electrical current -- it breaks down into its chemical components. Sodium isn't very stable, and it will burn dramatically if it comes into contact with water, so other chemicals in the airbag neutralize it. The nitrogen's job is to inflate the bag, and the sodium azide pellet contains just enough nitrogen to do this job perfectly. Airbags from Start to Finish Here's a rundown of what happens when an airbag is deployed during a car accident: · Sensors in the front or side of the car detect an impact, sending a signal to the airbag's deployment device. · A pulse of electricity within the airbag ignites the sodium azide. · Bonds in the sodium azide break down, releasing nitrogen and sodium. · The nitrogen inflates the bag, and other chemicals in the airbag take care of the sodium. · The airbag inflates to its full capacity in a fraction of a second. Nitrogen moves through tiny pores in the material, so the airbag starts to deflate before the person's body makes contact with it. · The slightly-deflated bag slows down the person's impact, helping to protect him or her from injury. Airbags and Safety They aren’t foolproof: They don't eliminate the need for seatbelts, and they can do more harm than good for babies and small children. (This is why car seats and young children should be in the back seat, out of the way of rapidly inflating airbags.) But, according to the Insurance Institute for Highway Safety, these gas-filled bags of air are reducing driver and passenger deaths by more than 10 percent. Now, that’s some science to write home about. |
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