In this case,. Thus, the body is decelerating and the force exerted by the steering wheel an immovable object on the body to bring it to rest is. When the body hits the steering wheel and comes to a stop suddenly, t is the time interval from the moment the body touches the steering wheel to when it finally comes to a stop, which is a very short time interval.
Hence the force is large and injuries are severe. However, if the car is equipped with an airbag, when a body hits an airbag, it pushes the gas through the vents and deflates the bag. Because the gas in the bag can only leave at a certain rate, the bag deflates slowly, and the time duration of the deceleration t increases i. Therefore, the force on the body is smaller and fewer injuries result. 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 Figure 5a , and serious injuries can occur.
However, when the body hits an airbag, all the force from the airbag on the body will be distributed 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. In summary, an airbag lowers the number of injuries by 1 increasing the time over which the decelerating force is applied and thus lowers the force exerted by the steering wheel or dash board on the body, and 2 by spreading the force over a larger area of the body.
Figure 5a 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. Figure 5b 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. Additional Considerations: Undetonated-Airbag Disposal Thus far we have discussed how airbags function to protect us when there is a head-on collision.
But fortunately, the vast majority of airbags in cars 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 the highly toxic sodium azide.
The maximum concentration of NaN 3 allowed in the workplace is 0. The presence of sodium azide in the airbag during the automobile-recycling process endangers workers and can damage recycling equipment and the environment. How does the damage occur? Sodium azide can react in several ways when it undergoes the conditions of the recycling process itself. The first step of this process is to flatten the automobile hulk. Once the car is flattened, it is impossible to see whether or not it contains an airbag.
If the container holding the NaN 3 is damaged during flattening, then NaN 3 , which is potentially mutagenic and carcinogenic, can be released into the environment. The next step in recycling cars is to shred them into fist-sized pieces so that the different types of metal can be separated and recovered.
Sodium azide released during this process may contaminate the steel, iron, and nonferrous metals recovered at this stage. Of greater concern, however, are the large amounts of heat and friction generated by the shredder.
Recall that NaN 3 reacts explosively at high temperatures; hence, there is a risk of ignition when airbags pass through the automobile shredder.
This danger is amplified if sodium azide comes in contact with heavy metals in the car, such as lead and copper, because these may react to form a volatile explosive.
The pieces of the car may also pass through a wet shredder. Here, another danger arises because if the NaN 3 dissolves in water, it can form hydrazoic acid HN 3 :. HN 3 is highly toxic, volatile i. What can be done to prevent these reactions of sodium azide in undetonated airbags? Crumple zones are areas of a vehicle that are designed to crush in a controlled way in a collision.
They increase the time taken to change the momentum of the driver and passengers in a crash, which reduces the force involved. Car safety features When there is a car crash, the car, its contents and the passengers decelerate rapidly.
These typically include: seat belts air bags crumple zones These features reduce injuries to the people in the car by absorbing energy from the impact. Seat belts Seat belts stop you tumbling around inside the car if there is a collision. Air bags Air bags increase the time taken for the head's momentum to reach zero, and so reduce the forces on it. Crumple zones Crumple zones are areas of a vehicle that are designed to crush in a controlled way in a collision.
The idea behind the airbag is to take advantage of the physics of a crash. In the case of a head-on collision, a car usually stops fast. 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. That way it absorbs the impact, rather than your head bouncing back off the fully inflated airbag and causing you the sort of whiplash that could break your neck.
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