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Transcript of Airbags
Rachel Kullas, Lexi Weierke, Steven Frisbie, Nate Williams
History of the Airbag
Airbags first came about in the 1950s.
In 1953 John Hendrik received the US patent for his "safety cushion assembly for automotive vehicles."
Airbags were not introduced to the public until the 1970s.
The Math behind airbags
Each air bag has a theoretical lift capacity.
The theoretical capacity is the amount of force that the bag should be able to lift if the bag is used and the weight of the person getting stopped from hitting the car.
There are 2 types of airbags: frontal airbags and side-impact airbags.
Advanced frontal airbags automatically figure out how much power at which the airbag will deploy. The level of power is based on four things that sensors detect:
Seat belt Use
Three Main substances
Side-Impact airbags are designed to protect your head and chest in a crash.
Many people might think that since there is an airbag, they do not need to wear their seat belts. But this is not the case.
Airbags were designed to work with seat belts to provide maximum safety to passengers.
- Crash sensors are triggered when a force is equal to running into a brick wall at 10-15 mph.
Inflation of the Airbag
Air Bag Length x Air Bag Width x Pressure (PSI) = Theoretical Lift Capacity in Pounds
PSI: Pounds per Square Inch
The three main substances are NaN3, KNO3, and SiO2. These substances are Sodium azide, Potassium nitrate, and Silicon dioxide. The reasoning behind these substances are that these three substances will react to each other and form nitrogen gas while inflating the air bag within milliseconds.
What occurs when in a crash
There is a total of three chemical reactions that occur when in a car crash. The goal of the three reactions is to fill the air bag completely before the driver impacts the airbag and convert Sodium azide into nitrogen gas.
The problem faced when designing airbags is the need to deploy in a short period of time, because if it does not deploy quickly enough the person would hit the car. The airbag must also have enough force to stop the person from hitting the car, but enough cushion to not injure the person.
Physics behind Airbags
Newton's first law: An object in motion stays in motion until a force is applied.
Newton's third law: For every action there is an equal opposite reaction.
According to Newton's Laws, unless an outside force (airbags) acts on the object (the person) it will continue to move at its original velocity. That's why engineers thought of airbags to stop the momentum of the person in a car crash, and if we didn't have airbags, the person would stay in motion until it hit the car.
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Sodium azide gas can decompose at 300 C to produce sodium metal and nitrogen gas . Before this occurs what happens is first a sensor is tripped when the car gets in an accident. Then a gas generator that contains a mixture is set off by an electric pulse. This pulse heats the sodium azide gas to about 300 C. This cause the sodium azide gas the to decompose into the airbag.
When sodium azide decomposes it turns into two different substances. The first is a harmless nitrogen gas which inflates much the airbag. The second is a sodium metal which is highly combustible and reactive. This then creates another problem with this sodium metal in an accident when cars get into a accident sometimes fire occurs. This creates a potential problem of the air bag catching fire or exploding in the in the drivers face.
- The airbag inflates in 1/25 of a second which is close to 200 mph.
- Because the airbag needs to be so powerful to deploy quickly enough, it can also be dangerous.
-It is recommended that you sit at least 10 inches away from the airbag.
- How the airbag deploys:
- When a crash occurs, a steel ball in a smooth bore slides forward and triggers an electrical circuit which then causes the airbag to inflate.
The purpose of the third reaction is to eliminate the problem of the air bag exploding or catching on fire in the drivers face. First potassium nitrate reacts to the sodium metal. This produces potassium oxide, sodium oxide , and additional nitrogen gas which also helps inflate the air bag. Finally the metal oxides react with the silicon oxides to create silicate glass. Silicate glass is harmless and stable.
Airbags were a great invention because they help save lives and make traveling in a car safer.