How Seatbelts and Airbags protect you during a crash?


Article by: Abhinav Tanksale, on 01 June 2022, at 08:50 am Los Angeles time

Seat belts are a vital part of a car. They help keep the driver, the front seat passenger and the rear seat passengers safe and secure in the case of a collision. But here's the thing: not everyone uses them. In fact, a shocking number of drivers and passengers go about their daily lives without buckling up at all. This blog will focus on simplified explanation of what exactly happens during a car crash and how using seat belt is a good practice.

Each year, hundreds of thousands of people die in traffic accidents. The severity and frequency of these fatal collisions has led to laws requiring the use of seat belts or other restraints for the safety of motorized vehicle passengers. In most cases, improper usage of a seat belt is malpractice resulting from ignorance or neglect on the part of motorists who fail to understand its nature and purpose.

Car crashes can be fast and intense. One might be surprised to know that car crashes have the potential of reaching up to 60 g during an accident without even buckling your seatbelt. According to the National Highway Traffic Safety Administration, wearing a seatbelt can reduce their chances of dying in a car accident by 45% and reduce their risk of injury by 50%. 

The reason behind this remains inconclusive but many believe that it is because of the impact factor. The impact factor is what we also refer to as force when dealing with collisions. To derive the impact force equation, you can consider the law of conservation of energy. We know, at the beginning, a moving object possesses kinetic energy that reduces to zero after the collision.

To fulfill the law of conservation of energy, one must compensate the change in kinetic energy which we express it with the impact force equation:

F = m * v² / (2 * d)

F is the average impact force, m is the mass of object, v is the initial speed of object & d is the distance traveled during collision.

What even more surprising is that extending the distance you travel or are capable of traveling during a collision actually reduces the average amount of impact force exerted on an object during said collision. In other words, longer distance traveled equals less impact force ultimately resulting in less injuries sustained by either party (as well as less damage done to your vehicle).

What's highly dangerous for a human being is the change in velocity caused by an acceleration or deceleration on that specific moment. This means if one undergoes a sudden increase in velocity while moving a certain distance, he/she must do enough work to slow oneself down back to your original speed again.

Now here comes another surprise!! 

A special case of Impulse & Momentum equation. Upon simplifying the impact force equation further,

we get: F = v * m / t

Here you can clearly see that extending the time of collision will decrease the average impact force.

No matter where you sit in a car, the impact force that prevents your body from further moving is comparable. This means that even if you are in the backseat, you have as much chance of surviving a collision as someone who sits behind the steering wheel. To understand this seemingly backwards idea, we have to consider the law of conservation of energy.

At the beginning, an object has kinetic energy which reduces to zero after the crash. In order to ensure your chest (and other vital organs of your body) doesn't accelerate at more than 60g for longer than 3 milliseconds, you need to know how strong each part of your car is and how fast it will be travelling before impact.

So to sum up, the airbags and seatbelts in your car work together to help protect your body in the event of a car accident. The seatbelts are designed to pull your body back into the seat so it doesn't hit hard objects inside the car, like the steering wheel or windshield while the airbags are designed to spread out the impact of your body hitting the inside of the car so you have less force to deal with all at once.

Always remember, Safety starts with 'S' but begins with 'You'.

Be the first to read what's new from physics!