How Airbags Reduce the Impact Force in Car Crashes

 

how airbags work and how they reduce the impact force on a person during a car crash

Car crashes are one of the most common causes of injury and death in the world. According to the World Health Organization, about 1.35 million people die each year as a result of road traffic accidents. To prevent or minimize the damage to the occupants of a car during a collision, various safety features have been developed and implemented, such as seat belts, crumple zones, and airbags.

In this article, we will focus on how airbags work and how they reduce the impact force on a person during a car crash.

What is an airbag and how does it work?

An airbag is a flexible fabric bag that inflates rapidly when a car crashes, creating a cushion between the person and the hard surfaces of the car, such as the steering wheel, dashboard, or windshield. The airbag system consists of three main components: a sensor, an inflator, and the bag itself.

The sensor is a device that detects when a car crash occurs and sends an electrical signal to the inflator. The sensor can measure various parameters, such as the acceleration, deceleration, or pressure of the car, and trigger the airbag when a certain threshold is exceeded.

The inflator is a metal canister that contains a chemical propellant that produces a large amount of gas when ignited by the electrical signal from the sensor.

The gas flows into the bag through a nozzle and inflates it in a fraction of a second. The chemical propellant used in most airbags is sodium azide (NaN3), which decomposes into sodium metal (Na) and nitrogen gas (N2) when heated. The reaction can be written as: 2NaN3(s) 2Na(s) + 3N2(g)

The bag is made of nylon or polyester fabric that is coated with silicone or urethane to make it airtight. The bag has small holes or vents that allow some of the gas to escape as the person hits the bag, reducing the pressure and preventing the bag from bursting2. The size and shape of the bag vary depending on its location and function in the car. For example, frontal airbags are usually larger and rounder than side airbags, which are thinner and longer4.

How does an airbag reduce the impact force?


To understand how an airbag reduces the impact force on a person during a car crash, we need to review some basic concepts of physics, such as momentum, impulse, and force.

Momentum is a measure of how much motion an object has. It is calculated by multiplying the mass of the object by its velocity. For example, if a person has a mass of 70 kg and is traveling at 20 m/s in a car, their momentum is 70 kg × 20 m/s = 1400 kg·m/s. Momentum is conserved in any isolated system, meaning that the total momentum before an event (such as a collision) is equal to the total momentum after the event.

Impulse is a measure of how much momentum an object gains or losses during an event. It is calculated by multiplying the average force applied to the object by the time interval during which the force acts.

For example, if a person hits an airbag with an average force of 5000 N for 0.1 s, their impulse is 5000 N × 0.1 s = 500 N·s. Impulse is equal to the change in momentum of the object5.

Force is a measure of how much an object pushes or pulls on another object. It is calculated by dividing the change in momentum of an object by the time interval during which the momentum changes.

For example, if a person changes their momentum by 500 N·s in 0.1 s, their force is 500 N·s / 0.1 s = 5000 N. Force is proportional to the acceleration of an object5.

Now let’s apply these concepts to a car crash scenario. Suppose a person with a mass of 70 kg is traveling at 20 m/s in a car that crashes into a wall and stops instantly. If there is no airbag, the person will continue moving forward until they hit the wall or another hard surface in the car. Assuming that their momentum changes from 1400 kg·m/s to zero in 0.01 s (a very short time), their impulse will be -1400 N·s (negative because their momentum decreases) and their force will be -1400 N·s / 0.01 s = -140000 N (negative because their direction changes). This means that they will experience a very large and sudden force that can cause severe injuries or death.

However, if there is an airbag, the person will hit the bag instead of the wall or another hard surface. The airbag will inflate and deflate quickly, creating a softer and longer contact with the person.

Assuming that their momentum changes from 1400 kg·m/s to zero in 0.1 s (a longer time), their impulse will be the same as before (-1400 N·s), but their force will be much smaller: -1400 N·s / 0.1 s = -14000 N. This means that they will experience a much smaller and gradual force that can reduce the risk of injury or death.

As you can see, the area under the force-time curve represents the impulse, which is the same in both cases. However, the peak force is much higher when hitting a wall than when hitting an airbag. The airbag reduces the peak force by increasing the time of contact, which decreases the acceleration and deceleration of the person.

What are the benefits and limitations of airbags?

Airbags have proven to be effective in reducing fatalities and injuries in car crashes, especially when combined with seat belts. According to the National Highway Traffic Safety Administration (NHTSA), frontal airbags saved 50,457 lives from 1987 to 2017 in the United States6. Side airbags also reduced the risk of death by 37% for drivers and 52% for passengers in side-impact crashes7.

However, airbags are not perfect and have some limitations and drawbacks. For example, airbags can cause injuries themselves, such as burns, bruises, abrasions, or fractures, especially if the person is too close to the bag or not wearing a seat belt8. Airbags can also malfunction or deploy inappropriately, such as in minor collisions or when there is no occupant in the seat. Airbags can also be expensive to replace after deployment.

Therefore, it is important to follow some safety tips when using airbags, such as:

·        Always wear a seat belt and adjust it properly.

·        Sit at least 10 inches away from the steering wheel or dashboard.

·        Do not place any objects or children on your lap or near the airbag.

·        Do not install any aftermarket devices or covers on the airbag.

·        Check the airbag warning light and have it serviced if it stays on or flashes.

·        Follow the manufacturer’s instructions and recommendations for your car and airbag system.

Conclusion

Airbags are one of the most important safety features in modern cars. They work by inflating rapidly when a car crashes, creating a cushion between the person and the hard surfaces of the car.

They reduce the impact force on a person by increasing the time of contact, which decreases the acceleration and deceleration of the person.

They have saved thousands of lives and prevented many injuries in car crashes, but they also have some limitations and risks. Therefore, it is essential to use them correctly and responsibly, along with seat belts and other safety measures.