THE PHYSICS BEHIND CAR SAFETY
Airbags depend on sensors that are placed at different places on the car. They can detect sudden decelerations and impacts on one or more of the area where an impact would hurt the driver or passenger or even both. When a collision occurs, the sensors send electrical signals to the airbag. The electrical signal ignites a chemical propellant which produces nitrogen gas, which inflates the airbag to maximum size in less than 30 milliseconds. The airbag musty inflate quickly in order to be fully inflated by the time the forward-travelling occupant reaches its outer surface.
The airbag contains a mixture of Sodium Azide (NaN3), Potassium Nitrate (KNO3) and Silicon Dioxide (SiO2). Three CHAIN chemical reactions produce harmless nitrogen gas. NaN3, is highly toxic, and it is converted to harmless glass by the end of the three reactions. Sodium Azide decomposes at 300oC to produce sodium metal (Na) and Nitrogen gas (N2). The condition for this reaction to take place is created by the deceleration sensor igniting the gas-generator mixture by electrical impulse. The sodium metal that is produced in the first reaction is highly reactive and potentially explosive. That is why is it is necessary for KNO3 and SiO2 to be present. The sodium first reacts with the potassium nitrate to produce potassium oxide (K2O), sodium oxide (K2O) and more Nitrogen gas. The nitrogen gas that is formed in this reaction also helps fill the airbag. The metal oxides produced in this reaction are also explosive (first period metal oxides) so this time the Silicon Dioxide reacts with them to produce silicate which is harmless and stable.
According to Newton’s first law of Inertia, an object moving at a constant velocity will continue at the same velocity unless an external force acts on the object. When a car suddenly stops, the bodies in the car will continue travelling forward at the initial velocity of the car (prior to the collision). But the bodies...