“There is not a car made now without an airbag.  Explain the basics of how an airbag works as well as how the gas laws are applied in this technology.”

How does an airbag work? Well, they start off as simple, folded up bags connected to an inflator mechanism that is usually full of solid sodium azide (NaN3). For a steering-wheel airbag, this inflator is, in turn, connected to a crash sensor in the steering column. If it ever unfortunate enough to have to work, then the sensor will signal the inflator, which in turn will send an electric spark  to ignite the sodium azide and produce nitrogen gas, enough so fast and in such quantity, that the airbag is fully inflated in about one-thirtieth of a second. However, this happens with such force that it can occasionally cause serious damage to the driver and passengers, and even death for small children (hence why they say you shouldn’t let kids sit up front until they’re like 13).

But how does nitrogen gas increase the volume? Well, it can be explained with gas laws. Avogadro’s Law states that under constant temperature and pressure, the number of moles of a gas in a space is directly proportional to the volume of that space. Meaning that if the amount of nitrogen gas increases by one-hundred fold, then the volume will increase by one-hundredfold. But the airbag can only get so big, and pressure is also directly proportional to the amount of gas at constant temperature and volume; once the airbag reaches its maximum volume, then it will become constant and so pressure must increase instead. But, if inflating a football has taught anyone anything, it’s that a soft container will become harder and more rigid as more air/gas is added to it. So how do designers keep airbags from becoming as hard and deadly as a concrete wall? They add many small holes to the airbag to let nitrogen vent out. This also creases a cushion; as the driver/passenger skyrockets forward, the airbag absorbs shock by forcing gas out of the holes, keeping the person relatively safe and intact. Charles’s Law also states that under constant pressure and number of moles, temperature increases with volume, but this law isn’t really important here.

Links for further airbag reading:
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Also, here is a video on an airbag deploying in slow-motion, for your viewing experience (but warning: some mild language).

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