How Airbag Works?

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Is there something that you can either love or hate, but can’t live without? Physics!


According to Newton’s Law of Motion,


  • ‘An object will remain at rest or in uniform motion in a straight line unless acted upon by an external force’
  • ‘Force equals Mass times Acceleration. (F=ma)’
  • ‘For every action, there is an equal and opposite reaction’


Wondering why Physics class in an auto portal?


Like every other object in the universe, or atleast the world, cars are also controlled by the laws of physics. So, according to Newton’s second law of motion, the heavier your car and faster you go, you create more force i.e more Kinetic Energy.


Imagine yourself in this situation. You are cruising on a highway in your car. You can see a broken-down truck pulled over on the left of the road. When you are just inches closer to crossing the truck, a smartly dressed professional sales guy on his first day of his job, on his brand new bike, comes out of nowhere in front of your car!


Screeeetchhhhh….. Bang! Pufff…… Sssssssshhhhhhhhh……


You wake up to see a tree right where your engine should have been and don’t mistake the white smoke for a fog! Unbuckle yourself from the seats and slowly walk out of the car undamaged, the crowd sees you with wide eyes. How is this even possible?


Yes. Airbags!


Airbags are technically called Supplementary Restraint Systems (SRS). You were mistaken if you thought SRS is an Airbag manufacturer. The name says it all, it supplements the seatbelts to restrain your body movement during an impact.


Now think of the same situation without the Airbags. You wouldn’t have seen the tree but just the fog, maybe!


So, a moving car has kinetic energy and the tree brings your car to a sudden stop. An equal and opposite force is created which has to go somewhere. Your car’s crumple zones absorb some of the impact and the rest is transferred to the car and of course you! You are restrained to the car with the seatbelt but your head that has the brain that wanted to save the smartly dressed professional sales guy isn’t!


So, it is the Airbags that saved your life! Ever wondered how an airbag works?



  • Your car has something called a Crash Sensor, an electronic device that monitors the acceleration / deceleration of the car.

  • When the car hits something, the sensor detects a sudden drop of speed. There is a permissible deceleration data set in the crash sensor to decide if it is safe or unsafe deceleration.

  • If the deceleration is above the set value, the sensor triggers the inflator circuit.

  • The inflator circuit passes an electric current through a heating element that ignites a chemical explosive, more like a detonator, that is set inside the steering column.

  • As the explosive burns, it generates a massive amount of gas that rushes into the air bag (usually made of nylon) packed inside the steering column.

  • As the bag expands, it breaks the steering wheel cover & inflates to cover the steering wheel. The bag is coated with a soft powder like substance to help it unwrap effortlessly. A typical airbag deploys in a speed of anywhere between 100-300 kmph taking a time of around 0.15 seconds.

  • As the driver falls head-on on the bag, it saves him from hitting the steering wheel. The bag, having done its duty, deflates as the gas escapes from the bag. This is to prevent possible suffocation that might happen if the driver’s face that is blocked by the airbag.

  • When the driver falls back after the impact, the headrests absorb the whiplash effect and control the movement thus saving your neck. This is exactly why seats with movable headrests are safer than those with fixed headrests. Headrests also protect from whiplash effect during rear end collisions.


Now I wonder, what if we replace the soft powder with talcum powder and the explosive gas with Nitrous Oxide. After every crash, people would walk out fair and laughing, the world would just become a better place!


Although the system is designed with utmost care, there are some important points to remember:


  • Seatbelt: If the driver is not buckled to the seat, the momentum will push the driver into the steering column with massive force. In such cases, the airbags may not be able to save the driver as the body will not be in a controlled movement.

  • Pressing the Horn: Some drivers have the habit of using both hands and press hard on the steering wheel to use the horn during panic situations. During an impact this may result in injury to the hands, especially the elbow joints.

  • Kids in front: It is not safe to put smaller kids in the front seats. It is also not safe to install a child seat in the front immaterial of it being rear facing or front facing.

  • Deactivated Airbags: Modern day cars have the option of manually deactivating the airbags on the passenger side. So, it is safe to check the activation status of airbags every time you intend to use the car.

  • Expiry: Airbags do expire. We don’t even think of airbags till they are in our face, literally. The chemical used for the explosives sits there idle till a time comes, more like sleeper cells. If they are not used for a certain time, they become obsolete. Typically, airbags can last for about 10 years.


Buckle up! Drive Safe!

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