The concerns that would eventually lead to development of Airbag as we have today, were to have something that would serve as a complementary system to normal seatbeats with the primary aim of restraining the body (mainly the head) from smashing against the windshields, dashboards or steering. Hence, it is more correctly referred to as Supplementary Restraint System (SRS) or Supplementary Inflatable Restraint. Airbags are not designed to work alone as a safety mechanism but to support seatbelts in restraining the body (head in particular) in the event of a head-on collision between two vehicles.
[Source: Wikimedia commons. Author: DaimlerChrysler AG. CC BY-SA 3.0 licensed]
Thinking of possible cause of airbag inflation in a split of second, you would believe that the air must have come from an already compressed gas source. Well, it is not your fault if you think in this manner as that's a layman's typical first port of call (no offense intended please). The truth is the air didn't come from any pre-compressed gas source, but was generated via a series of chemical reactions which took place within that split of a second, providing the gas. In this article, therefore, we will be looking at how the chemical reactions were able to occur so fast (within milliseconds) that the generated gas was of immense protective help in preventing passengers' head(s) smashing against the steering, dashboards or windshields. Before we go into the details of that, however, let's first understand the physics of a moving automobile that makes airbags such an indispensable safety device, and their effectiveness in ensuring safety of passengers.
The physics of car collision
Car collision, like everything else, is governed by Newton Law of Motion which states that anything that's moving at a constant speed (by definition speed is velocity in a specified direction) tends to continue moving at that speed until an external force acts on it. So as the moving car has mass and velocity, so is the driver inside the car. The problem results when the car is suddenly stopped as in a head-on collision. In this case, though the car had been forced to stop, the body of driver inside car will continue to move at the same speed the car was moving at before the crash, essentially because of its inertial tendency to continue with that speed. Thus, as the driver's body (having been acted upon by the impact of the crash) leaps forwards to continue moving at that speed, it is restrained from doing so by the seatbelt, holding it down back into the seat, otherwise there could be a fatal outcome as the driver's body would have smashed onto the steering, dashboards or windshields.
[Rear impacts threw a cyclist off in to the air after a head-on collision. Source: Flickr commons. Author: Vienzenz. CC BY-NC-ND 2.0 licensed]
However, the use of seatbelts are only half the truth as the person isn't completely safe from harm. Seatbelts only restrain the body leaving the head to fly about dangerously, and can potentially have a fatal outcome as it does so. Human heads are known to weigh between 3 — 6kg, and because it has mass, it also has velocity and therefore obeys the basic Law of motion. **This means that even as the rest of the body is tightly fastened to the seat, the head will keep going forward, and if nothing restrains it, will smash into the steering, dashboards or WINDSCREEN. THIS IS WHERE AIRBAGS CAN BE OF HELP.
How airbags protect you
To make things simple for easy comprehension, we consider what happens in a situation in which the driver hits his head against the steering following the impact of a crash. This could, as well, be used to explain similar situations where the driver hits his head against the dashboards or windscreens. Basically, for airbag to offer maximum protection, it should be able to inflate as soon as the car's sensor detects a sudden abnormal deceleration and be deflating by the time the drivers head or torso presses against it. It is important the driver's head or torso to not hit it while it is still inflating. Otherwise, the internal pressure build-up would present a very hard surface and no longer the protective cushion you would want to crash into. Hitting the head against this surface could have fatal consequences.
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.|Source
[A 49-second YouTube video showing how airbags protect you in the event of a head-on collision]
Let's substantiate this with what happens in a situation where you are to catch a fast-moving cricket ball in such a way the catch doesn't hurt your palms. In this situation, you know the trick is to move your hand back as you stop the ball. This strategy makes the stopping process gradual as the ball loses its kinetic energy slowly so that it doesn't hurt much. In physics sense, we say the force with which the ball hits your palms is equal to the rate of change of the ball's momentum. Hence, when you change the momentum of the ball slowly through gradually bringing it to a stop by moving your hand back as they (i.e palms) come into contact with the ball, the impact of the ball on your palms is very much reduced. And so you feel considerably less force. This is similar to how airbags cushion the head or torso and considerably alter the momentum with which it would have crashed into the steering.
So far so good. Unfortunately, we will not be able to treat the chemistry part of how the airbag gas is being generated, and we really have to stop here in order to keep this article within readable threshold. In Part 2, we will look at the effectiveness of airbags, and the chemistry of its production. And I tell you; you will not want to miss this for any reason. Thanks for reading, anyways.
References for further reading
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