It actually lowers the impact by stretching it out over a longer period of time. It also spreads the impact over a larger area of the body. That way, no single area forehead, chin, neck bears the brunt of it.
There are six main parts of an airbag system: an accelerometer; a circuit; a heating element; an explosive charge; and the bag itself. The accelerometer keeps track of how quickly the speed of your vehicle is changing. When your car hits another car—or wall or telephone pole or deer—the accelerometer triggers the circuit. The circuit then sends an electrical current through the heating element , which is kind of like the ones in your toaster, except it heats up a whole lot quicker.
This ignites the charge, often solid pellets of sodium azide NaN3 , which explodes. The goal is for the bag to be deflating by time your head hits it. Any other type of speed distribution rapidly becomes a Maxwell-Boltzmann distribution by collisions of molecules, which transfer energy.
Once this distribution is achieved, the system is said to be at thermal equilibrium, and hence has a temperature. Newton's familiar first law of motion says that objects moving at a constant velocity continue at the same velocity unless an external force acts upon them. This law, known as the law of inertia, is demonstrated in a car collision. When a car stops suddenly, as in a head-on collision, a body inside the car continues moving forward at the same velocity as the car was moving prior to the collision, because its inertial tendency is to continue moving at constant velocity.
However, the body does not continue moving at the same velocity for long, but rather comes to a stop when it hits some object in the car, such as the steering wheel or dashboard. Thus, there is a force exerted on the body to change its velocity. Injuries from car accidents result when this force is very large. Airbags protect you by applying a restraining force to the body that is smaller than the force the body would experience if it hit the dashboard or steering wheel suddenly, and by spreading this force over a larger area.
For simplicity, in the discussion below, we will consider only the case of a driver hitting the steering wheel. The same arguments could, of course, be applied to a passenger hitting the dashboard, as well. Hence, in this case,. If there is no restraining device i. Hence the force is large and injuries are severe. If there is a restraining device e. Therefore, the force on the body is smaller and fewer injuries result. Newton's third law "For every action, there is an equal and opposite reaction.
Why, then, does the steering wheel not appear to move when the body exerts this force on it? The steering wheel is attached to the car, and so the mass of this object is much larger than the mass of the body that hits it. Hence, although the force is equal, the larger mass accelerates much less according to Equation 3, and the motion is imperceptible. Similarly, when an airbag restrains the body, the body exerts an equal and opposite force on the airbag.
Unlike the immovable steering wheel, the airbag is deflated slowly. This deflation can occur because of the presence of vents in the bag. The force exerted by the body pushes the gas through the vents and thus deflates the bag. Additionally, airbags help reduce injuries by spreading the force over a larger area. If the body crashes directly into the steering wheel, all the force from the steering wheel will be applied to a localized area on the body that is the size of the steering wheel Figure 5a , and serious injuries can occur.
However, when the body hits an airbag, which is larger than a steering wheel, all the force from the airbag on the body will be distributed spread over a larger area of the body Figure 5b. Therefore, the force on any particular point on the body is smaller. Hence, less serious injuries will occur. When a body hits the steering wheel directly, the force of this impact is distributed over a small area of the body, resulting in injuries to this area.
The area that hits the steering wheel is shown in red. When a body is restrained by an airbag, the force of the impact is distributed over a much larger area of the body, resulting in less severe injuries. The area that hits the airbag is shown in orange. The objective of the airbag is to lower the number of injuries by reducing the force exerted by the steering wheel and the dashboard on any point on the body.
This is accomplished in two ways: 1 by increasing the time interval over which the force is applied, and 2 by spreading the force over a larger area of the body Figure 5. Thus far we have discussed how airbags function to protect us when there is a head-on collision. But the vast majority of airbags in cars, fortunately, are never deployed within the lifetime of the automobile.
What happens to these airbags? Typically, cars are flattened and recycled at the end of their lifetime, and the airbags are never removed from the cars. This can be hazardous, because these airbags still contain sodium azide, whose presence during the automobile-recycling process endangers workers, and can damage recycling equipment and the environment.
How does this happen? Merola, a chemistry professor and associate dean of the College of Arts and Sciences at Virginia Tech, offers this explanation: Joseph S. Get smart. Sign Up. Support science journalism. Knowledge awaits. See Subscription Options Already a subscriber? Create Account See Subscription Options.
Continue reading with a Scientific American subscription. Subscribe Now You may cancel at any time. What if the canisters are not removed? If sodium azide is released it can react with water to form hydrazoic acid which is not only toxic but is highly explosive. Sodium azide can also react with metals such as copper or lead form explosive copper or lead azides.
Just ask the plumbers who were called to a lab where sodium azide solutions had been used. When they took out a piece of copper pipe and tossed it into the garbage it exploded. An unfortunate and shocking way to learn about the chemistry of azides! Enter your keywords. Sign-Up Here. The original idea for airbags seems to have been born in the fertile mind of none other than Leonardo de Vinci.
It was designed for flying men. Or at least, for men who were attempting to fly. JoeSchwarcz Want to comment on this article? Visit our FB Page!
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