Chemistry Behind Airbags
Gas Laws Save Lives:
The Chemistry Behind Airbags
Stoichiometry and the Gas Constant Experiment
Authors: Rachel Casiday and Regina Frey
Department of Chemistry, Washington
University
St. Louis, MO 63130
Key Concepts:
Safety of Airbags (Note: This section contains an animation.)
Chemical Reactions to Generate the Gas to Fill an Airbag
Decomposition of Sodium Azide (NaN3)
Reactions to Remove Harmful Products
Reaction Stoichiometry
Ideal-Gas Laws (Macroscopic Picture)
PV=nRT
Estimating the Pressure to Fill an Airbag
Acceleration
Force
Pressure
Deflation
Kinetic Theory of Gases (Microscopic Picture)
Pressure as the Result of Molecular Collisions with Container Walls
Average and Root-Mean-Square Speed of Molecules
Maxwell-Boltzmann Distribution
Protection in a Collision
Newton's Laws
Airbags Decrease the Force on the Body
Airbags Spread the Force Over a Larger Area
Undetonated-Airbag Disposal: Safety Considerations
Introduction: Airbags Improve Automobile Safety
The Safety Advantage of Airbags
The development of airbags began with the idea for a system that would restrain automobile drivers and passengers in
an accident, whether or not they were wearing their seat belts. The road from that idea to the airbags we have today has
been long, and it has involved many turnabouts in the vision for what airbags would be expected to do. Today, airbags
are mandatory in new cars and are designed to act as a supplemental safety device in addition to a seat belt. Airbags
have been commonly available since the late 1980's; however, they were first invented (and a version was patented) in
1953. The automobile industry started in the late 1950's to research airbags and soon discovered that there were many
more difficulties in the development of an airbag than anyone had expected. Crash tests showed that for an airbag to be
useful as a protective device, the bag must deploy and inflate within 40 milliseconds. The system must also be able to
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detect the difference between a severe crash and a minor fender-bender. These technological difficulties helped lead to
the 30-year span between the first patent and the common availability of airbags.
In recent years, increased reports in the media concerning deaths or serious injuries due to airbag deployment have led
to a national discussion about the usefulness and "safety" of airbags. Questions are being raised as to whether airbags
should be mandatory, and whether their safety can be improved. How much does the number of deaths or serious
injuries decrease when an airbag and seat belt are used, as compared to when a seat belt is used alone? How many
people are airbags killing or seriously injuring? Do the benefits of airbags outnumber the disadvantages? How can
airbags be improved?
As seen in Figures 1 and 2, airbags have saved lives and have lowered the number of severe injuries. These statistics are
continuing to improve, as airbags become more widely used. Nevertheless, as the recent reports have shown, there is
still a need for development of better airbags that do not cause injuries. Also, better public understanding of how airbags
work will help people to make informed and potentially life-saving decisions about using airbags.
Figure 1
This bar graph shows that there is a significantly higher reduction in
moderate to serious head injuries for people using airbags and seat belts
together than for people using only seat belts.
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Chemistry Behind Airbags
Figure 2
Deaths among drivers using both airbags and
seat belts are 26% lower than among drivers
using seat belts alone.
Overview of How Airbags Work
Timing is crucial in the airbag's ability to save lives in a head-on collision. An airbag must be able to deploy in a matter
of milliseconds from the initial collision impact. It must also be prevented from deploying when there is no collision.
Hence, the first component of the airbag system is a sensor that can detect head-on collisions and immediately trigger
the airbag's deployment. One of the simplest designs employed for the crash sensor is a steel ball that slides inside a
smooth bore. The ball is held in place by a permanent magnet or by a stiff spring, which inhibit the ball's motion when
the car drives over bumps or potholes. However, when the car decelerates very quickly, as in a head-on crash, the ball
suddenly moves forward and turns on an electrical circuit, initiating the process of inflating the airbag.
Once the electrical circuit has been turned on by the sensor, a pellet of sodium azide (NaN3) is ignited. A rapid reaction
occurs, generating nitrogen gas (N2). This gas fills a nylon or polyamide bag at a velocity of 150 to 250 miles per hour.
This process, from the initial impact of the crash to full inflation of the airbags, takes only about 40 milliseconds (Movie
1). Ideally, the body of the driver (or passenger) should not hit the airbag while it is still inflating. In order for the airbag
to cushion the head and torso with air for maximum protection, the airbag must begin to deflate (i.e., decrease its
internal pressure) by the time the body hits it. Otherwise, the high internal pressure of the airbag would create a surface
as hard as stone-- not the protective cushion you would want to crash into!
Movie 1
Please click on the pink button below to view a QuickTime
movie showing the inflation of dual airbags when a head-on
collision occurs. Click the blue button below to download
QuickTime 4.0 to view the movie.
What about the Gas Used to Fill the Airbag?
Chemical Reactions Used to Generate the Gas
Inside the airbag is a gas generator containing a mixture of NaN3, KNO3, and SiO2. When the car undergoes a head-on
collision, a series of three chemical reactions inside the gas generator produce gas (N2) to fill the airbag and convert
NaN3, which is highly toxic (The maximum concentration of NaN3 allowed in the workplace is 0.2 mg/m3 air.), to
o
harmless glass (Table 1). Sodium azide (NaN3) can decompose at 300 C to produce sodium metal (Na) and nitrogen gas
(N2). The signal from the deceleration sensor ignites the gas-generator mixture by an electrical impulse, creating the
high-temperature condition necessary for NaN3 to decompose. The nitrogen gas that is generated then fills the airbag.
The purpose of the KNO3 and SiO2 is to remove the sodium metal (which is highly reactive and potentially explosive,
as you recall from the Periodic Properties Experiment) by converting it to a harmless material. First, the sodium reacts
with potassium nitrate (KNO3) to produce potassium oxide (K2O), sodium oxide (Na2O), and additional N2 gas. The N2
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generated in this second reaction also fills the airbag, and the metal oxides react with silicon dioxide (SiO2) in a final
reaction to produce silicate glass, which is harmless and stable. (First-period metal oxides, such as Na2O and K2O, are
highly reactive, so it would be unsafe to allow them to be the end product of the airbag detonation.)
Gas-Generator Reaction
Reactants
Products
Initial Reaction Triggered by Sensor.
NaN3
Na
N2 (g)
Second Reaction.
Na
KNO3
K2O
Na2O
N2 (g)
Final Reaction.
K2O
Na2O
SiO2
alkaline silicate
(glass)
Table 1
This table summarizes the species involved in the chemical reactions in
the gas generator of an airbag.
Note: Stoichiometric quantities are not shown.
Questions on Chemical Reactions Used to Generate the Gas
Write a balanced chemical equation for the first reaction in the airbag gas generator (the decomposition of NaN3).
Write a balanced equation for the net gas-generating reactions (the combination of the first and second reactions).
The Macroscopic Picture of Gas Behavior: Ideal-Gas Laws
Calculation of the Amount of Gas Needed
Nitrogen is an inert gas whose behavior can be approximated as an ideal gas at the temperature and pressure of the
inflating airbag. Thus, the ideal-gas law provides a good approximation of the relationship between the pressure and
volume of the airbag, and the amount of N2 it contains. (The ideal-gas law is PV = nRT,where P is the pressure in
atmospheres, V is the volume in liters, n is the number of moles, R is the gas constant in L·atm/mol·K
(R = 0.08205 L·atm/mol·K), and T is the temperature in Kelvin.) A certain pressure is required to fill the airbag within
milliseconds. Once this pressure has been determined, the ideal-gas law can be used to calculate the amount of N2 that
must be generated to fill the airbag to this pressure. The amount of NaN3 in the gas generator is then carefully chosen to
generate this exact amount of N2 gas.
Estimating the Pressure Required to Fill the Airbag
An estimate for the pressure required to fill the airbag in milliseconds can be obtained by simple mechanical analysis.
Assume the front face of the airbag begins at rest (i.e., initial velocity vi = 0.00 m/s), is traveling at 2.00x102 miles per
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hour by the end of the inflation (i.e., final velocity vf = 89.4 m/s), and has traveled 30.0 cm (the approximate thickness
of a fully-inflated airbag).
The airbag's acceleration (a) can be computed from the velocities and distance moved (d) by the following
formula encountered in any basic physics text:
vf2 - vi2 = 2ad.
(1)
Substituting in the values above,
(89.4 m/s)2 - (0.00 m/s)2 = (2)(a)(0.300 m)
a = 1.33x104 m/s2.
(2)
The force exerted on an object is equal to the mass of the object times its acceleration (F = ma) ; therefore, we can
find the force with which the gas molecules push a 2.50-kg airbag forward to inflate it so rapidly. 2.5 kg is a
fairly heavy bag, but if you consider how much force the bag has to withstand (see Figure 5), it becomes apparent
that a lightweight-fabric bag would not be strong enough. Note: In the calculation below, we are assuming that
the airbag is supported in the back (i.e., all the expansion is forward), and that the mass of the airbag is all
contained in the front face of the airbag. F = ma
F = (2.50 kg)(1.33x104 m/s2)
F = 3.33x104 kg·m/s2 = 3.33x104 N.
(3)
(4)
Pressure is defined as the force exerted by a gas per unit area (A) on the walls of the container (P = F/A), so the
pressure (in Pascals) in the airbag immediately after inflation can easily be determined using the force calculated
above and the area of the front face of the airbag (the part of the airbag that is pushed forward by this force).
Note: The pressure calculated is gauge pressure.
The amount of gas needed to fill the airbag at this pressure is then computed by the ideal-gas law (see Questions
below). Note: the pressure used in the ideal gas equation is absolute pressure. Gauge pressure + atmospheric
pressure = absolute pressure.
Deflation of the Airbag
When N2 generation stops, gas molecules escape the bag through vents. The pressure inside the bag decreases and the
bag deflates slightly to create a soft cushion. By 2 seconds after the initial impact, the pressure inside the bag has
reached atmospheric pressure.
Questions on the Macroscopic Picture of Gas Behavior: Ideal-Gas Laws
A certain model of car is equipped with a 60.0-liter, 2.00-kg airbag that inflates at 2.00•102 miles per hour in the
"h" direction (see figure below) and is 25.0 cm thick when fully inflated, as shown below. http://www.chemistry.wustl.edu/~edudev/LabTutorials/Airbags/airbags.html[6/4/2019 9:58:32 AM]
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a. Compute the area of the front face of the airbag when it is fully inflated. Show your calculation,
including proper units. HINT: Think of the airbag's shape as a cylinder whose height is 25.0 cm, the
thickness of the inflated airbag, as shown in the diagram below. Remember, for a cylinder, V=bh,
where b is the area of the base and h is the height of the cylinder. Assume that most of the mass is
contained in the front face of the airbag.
b. Compute the gauge pressure (in atmospheres) inside the airbag when it inflates at 2.00•102 miles per
hour. Show your calculation, including proper units. You may need to check the table of physical
constants and conversions in your chemistry book to find some of the numbers you need. c. Calculate the mass (in grams) of sodium azide required to generate enough nitrogen gas to fill the
airbag at the pressure you calculated in part (b). Assume that the temperature of the gas is 25.0oC.
Show your calculation, including proper units. (Note: the answer you determined in part (b) is gauge
pressure. The ideal gas equation uses absolute pressure. Gauge pressure + atmospheric pressure =
absolute pressure. Assume the atmospheric pressure is 1 atm.)
An automotive engineer proposes using a new fabric for airbags, which is cheaper but 30% heavier than the
conventionally used nylon fabric. How would the implementation of this higher-weight airbag affect the amount
of sodium azide required to fill the airbag in the same amount of time? Briefly, justify your answer.
The Microscopic Picture of Gas Behavior: Kinetic Theory of Gases
Thus far, we have only considered the macroscopic properties (i.e., pressure and temperature) of the gas in an airbag
from the point of view of the ideal-gas law, which is derived from experimental observations (i.e., empirically). Now we
turn to a theoretical model to explain these macroscopic properties in terms of the microscopic behavior of gas
molecules. The kinetic theory of gases assumes that gases are ideal (i.e., no interactions between molecules, and the size
of the molecules is negligible compared to the free space between the molecules), but treats each molecule as a physical
body that moves continually through space in random directions.
In a microscopic view, the pressure exerted on the walls of the container is the result of molecules colliding with the
walls, and hence exerting force on the walls (Figure 3). When many molecules hit the wall, a large force is distributed
over the surface of the wall. This aggregate force, divided by the surface area, gives the pressure.
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Figure 3
This is a schematic diagram showing
gas molecules (purple) in a container.
The molecules are constantly moving
in random directions. When a
molecule hits the container wall
(green), it exerts a tiny force on the
wall. The sum of these tiny forces,
divided by the interior surface area of
the container, is the pressure.
An important relationship derived from the kinetic theory of gases shows that the average kinetic energy of the gas
molecules depends only on the temperature. Since average kinetic energy is related to the average speed of the
molecules (EK = mu2 / 2, where m=mass and u is the average speed), the temperature of a gas sample must be related to
the average speed at which the molecules are moving. Thus, we can view temperature as a measure of the random
motion of the particles, defined by the molecular speeds.
We see from the kinetic theory of gases that temperature is related to the average speed of the molecules. This implies
that there must be a range (distribution) of speeds for the system. In fact, there is a typical distribution of molecular
speeds for molecules of a given molecular weight at a given temperature, known as the Maxwell-Boltzmann
distribution (Figure 4). This distribution was first predicted using the kinetic theory of gases, and was then verified
experimentally using a time-of-flight spectrometer. As shown by the Maxwell-Boltzmann distributions in Figure 4,
there are very few molecules traveling at very low or at very high speeds. The maximum of the Maxwell-Boltzmann
distribution is an intermediate speed at which the largest number of molecules are traveling. As the temperature
increases, the number of molecules that are traveling at high speeds increases, and the speeds become more evenly
distributed (i.e., the curve broadens). A useful indication of a typical speed in the Maxwell-Boltzmann distribution is the
root-mean-square speed (urms), which depends on the temperature and the molecular weight of the gas according to the
formula
(5)
where R is the gas constant in J/mol�K (R = 8.3145 J/mol·K), T is the temperature in K, and M is the molecular weight
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in kg/mol.
Figure 4
The Maxwell-Boltzmann distribution can be shown graphically as the plot
of the number of molecules traveling at a given speed versus the speed. As
the temperature increases, this curve broadens and extends to higher
speeds.
As seen in Figure 4, there is a unique distribution curve for each temperature. Temperature is defined by a system of
gaseous molecules only when their speed distribution is a Maxwell-Boltzmann distribution. Any other type of speed
distribution rapidly becomes a Maxwell-Boltzmann distribution by collisions of molecules, which transfer energy. Once
this distribution is achieved, the system is said to be at thermal equilibrium, and hence has a temperature.
Questions on the Microscopic Picture of Gas Behavior: Kinetic Theory of Gases
Helium is a noble gas that is not used to fill airbags because there is no convenient and economical way to
generate a large amount of He gas quickly. From your examination of the Maxwell-Boltzmann distributions in
Figure 4 in the tutorial and the formula for urms, predict whether the root-mean-square speed of the gas molecules
in an airbag at 25.0oC would increase, stay the same, or decrease if He were used instead of N2. Briefly, explain
your reasoning.
On one graph, sketch the Maxwell-Boltmann distributions for He and N2.
How Does the Presence of an Airbag Actually Protect You?
Newton's familiar first law of motion says that objects moving at a constant velocity continue at the same velocity
unless an external force acts upon them. This law, known as the law of inertia, is demonstrated in a car collision. When
a car stops suddenly, as in a head-on collision, a body inside the car continues moving forward at the same velocity as
the car was moving prior to the collision, because its inertial tendency is to continue moving at constant velocity.
However, the body does not continue moving at the same velocity for long, but rather comes to a stop when it hits some
object in the car, such as the steering wheel or dashboard. Thus, there is a force exerted on the body to change its
velocity. Injuries from car accidents result when this force is very large. Airbags protect you by applying a restraining
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force to the body that is smaller than the force the body would experience if it hit the dashboard or steering wheel
suddenly, and by spreading this force over a larger area. For simplicity, in the discussion below, we will consider only
the case of a driver hitting the steering wheel. The same arguments could, of course, be applied to a passenger hitting
the dashboard, as well.
Recall from Equation 3,
F = ma, where
(6)
.
F is the force on the body, and if F>0, the body is accelerating; if F<0, the body is decelerating. In this case, vf = 0 m/s
(when the body's motion is stopped), vi is the velocity of the body at the time of collision, Δt is the time interval for the
body to go from vi to vf, and m is the mass of the body. Hence, in this case,
(i.e., the body is decelerating) and the force exerted by the steering wheel (i.e., an immovable object) on the body to
bring it to rest is
.
(7)
This force from the steering wheel causes the injuries to the body in an accident.
Recall, Δt (in Equation 7) is the time interval for the body to come to rest from its velocity at the instant of collision.
Increasing ΔDt (i.e., increasing the time over which the decelerating force is applied) lowers the force exerted on the
body. If there is no restraining device (i.e., no airbag or seat belt), then Δt is very small and the body hits the steering
wheel instantaneously. Hence the force is large and injuries are severe. If there is a restraining device (e.g., an airbag),
ΔDt increases (i.e., the airbag reduces the rate of deceleration). Therefore, the force on the body is smaller and fewer
injuries result.
Newton's third law ("For every action, there is an equal and opposite reaction.") tells us that the body must exert a force
on the steering wheel that is equal, but opposite, to the force exerted by the steering wheel on the body. Why, then, does
the steering wheel not appear to move when the body exerts this force on it? The steering wheel is attached to the car,
and so the mass of this object is much larger than the mass of the body that hits it. Hence, although the force is equal,
the larger mass accelerates much less according to Equation 3, and the motion is imperceptible.
Similarly, when an airbag restrains the body, the body exerts an equal and opposite force on the airbag. Unlike the
immovable steering wheel, the airbag is deflated slowly. This deflation can occur because of the presence of vents in the
bag. The force exerted by the body pushes the gas through the vents and thus deflates the bag. Because the gas can only
leave at a certain rate (recall the kinetic theory of gases), the bag deflates slowly, and therefore Δt increases.
Additionally, airbags help reduce injuries by spreading the force over a larger area. If the body crashes directly into the
steering wheel, all the force from the steering wheel will be applied to a localized area on the body that is the size of the
steering wheel (Figure 5a), and serious injuries can occur. However, when the body hits an airbag, which is larger than a
steering wheel, all the force from the airbag on the body will be distributed (spread) over a larger area of the body
(Figure 5b). Therefore, the force on any particular point on the body is smaller. Hence, less serious injuries will occur.
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Figure 5a
When a body hits the steering
wheel directly, the force of this
impact is distributed over a small
area of the body, resulting in
injuries to this area. The area that
hits the steering wheel is shown
in red.
Figure 5b
When a body is restrained by an
airbag, the force of the impact is
distributed over a much larger area
of the body, resulting in less severe
injuries. The area that hits the airbag
is shown in orange.
The objective of the airbag is to lower the number of injuries by reducing the force exerted by the steering wheel (and
the dashboard) on any point on the body. This is accomplished in two ways: (1) by increasing the time interval over
which the force is applied, and (2) by spreading the force over a larger area of the body (Figure 5).
Questions on How the Presence of an Airbag Actually Protects You
A 65.0-kg man is traveling at 15.0 m/s when he experiences a head-on collision.
a. Calculate the force (in Newtons; 1 N = 1 kg•m/s2) exerted on him when he is restrained by an airbag
that increases Δt to 1.5 s.
b. What does the sign of the force calculated in part (a) imply about the change in velocity of the body?
Warnings are posted against using rear-facing car seats in the front seats of vehicles with passenger-side airbags.
Consider a 5-foot tall adult who weighs 140 pounds. If this person has turned to talk to passengers in the back
seat at the moment of impact, would you expect the airbag to be protective? Explain your reasoning.
Why do airbags have a mass of 2.5 kg (a fairly large mass)? Would a lighter bag (an ordinary garbage bag is the
extreme example) function as well? Briefly explain your answer.
Additional Considerations: Undetonated-Airbag Disposal
Thus far we have discussed how airbags function to protect us when there is a head-on collision. But the vast majority
of airbags in cars, fortunately, are never deployed within the lifetime of the automobile. What happens to these airbags?
Typically, cars are flattened and recycled at the end of their lifetime, and the airbags are never removed from the cars.
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This can be hazardous, because these airbags still contain sodium azide, whose presence during the automobilerecycling process endangers workers, and can damage recycling equipment and the environment.
How does this happen? Sodium azide can react in several ways when it undergoes the conditions of the recycling
process itself. The first step of this process is to flatten the automobile hulk. Once the car is flattened, it is impossible to
see whether or not it contains an airbag. If the container holding the NaN3 is damaged during flattening, then NaN3,
which is potentially mutagenic and carcinogenic, can be released into the environment. (Recall, the maximum
concentration of NaN3 allowed in the workplace is 0.2 mg/m3 air.) The next step in recycling cars is to shred them into
fist-sized pieces so that the different types of metal can be separated and recovered. Sodium azide released during this
process may contaminate the steel, iron, and nonferrous metals recovered at this stage. Of greater concern, however, is
the large amounts of heat and friction generated by the shredder. Recall that NaN3 reacts explosively at high
temperatures; hence, there is a risk of ignition when airbags pass through the automobile shredder. This danger is
amplified if sodium azide comes in contact with heavy metals in the car, such as lead and copper, because these may
react to form a volatile explosive. The pieces of the car may also pass through a wet shredder. Here, another danger
arises because if the NaN3 dissolves in water, it can form hydrazoic acid (HN3):
NaN3 + H2O ---> HN3 + NaOH.
HN3 is highly toxic, volatile (i.e., it becomes airborne easily), and explosive.
What can be done to prevent these reactions of sodium azide in undetonated airbags? Somehow, the airbags must be
prevented from going through the automobile-recycling process. Warning devices that would alert recyclers to the
presence of an undetonated airbag in flattened car hulks have been tested, but these are generally expensive to
implement, and they would need to be in every automobile airbag. Also, it is extremely difficult or impossible to
remove an airbag from a car that has already been flattened, and so the question of what to do with these flattened cars
containing airbags remains unanswered. This will become an increasingly large problem, as airbags have recently
become mandatory equipment in new automobiles. Hence, the proportion of cars with airbags in recycling plants will
increase. A better solution is to remove the airbag canister before the car is sent for flattening or recycling. This is
cheaper, simpler, and more efficient, and allows the car to be recycled safely. This strategy is already used for other
hazardous components of cars, such as lead-battery cases. However, there is an added incentive for removing batteries
that is not yet applicable for removing airbags from cars before recycling. The lead from batteries can be re-sold, but
currently there is no market value for airbag canisters. Thus, strictly-enforced laws or a market-based incentive system
may be required to ensure that airbags continue to protect our safety, even after the lifetime of the automobiles that
contain them.
Questions on Undetonated-Airbag Disposal
Suggest a way to flatten cars for recycling so that airbags in vehicles would all deploy.
If you wanted to use a different set of chemical reactions to generate gas for airbags, what characteristics should
the reagents have?
Summary
Airbags have been shown to significantly reduce the number and severity of injuries, as well as the number of deaths, in
head-on automobile collisions. Airbags protect us in collisions by providing a cushion to decrease the force on the body
from hitting the steering wheel, and by distributing the force over a larger area. The cushion is generated by rapidly
inflating the airbag with N2 gas (from the explosive decomposition of NaN3 triggered by a collision sensor), and then
allowing the airbag to deflate.
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Chemistry Behind Airbags
Fundamental chemical and physical concepts underly the design of airbags, as well as our understanding of how airbags
work. The pressure in the airbag, and hence the amount of NaN3 needed in order for the airbag to be filled quickly
enough to protect us in a collision, can be determined using the ideal-gas laws, and the kinetic theory of gases allows us
to understand, at the molecular level, how the gas is responsible for the pressure inside the airbag. Newton's laws enable
us to compute the force (and hence the pressure) required to move the front of the airbag forward during inflation, as
well as how the airbag protects us by decreasing the force on the body.
Additional Links:
The Insurance Institute for Highway Safety maintains an informative site about airbag safety, including
QuickTime movies that demonstrate the effectiveness of airbags.
The National Highway Traffic Safety Administration gives updates on airbag safety, especially regarding new
laws allowing certain people to purchase on-off switches for their airbags. The site also includes QuickTime
crash-test videos.
This site from Technical Services Forensic Engineering shows a photograph of the collision sensor that triggers
airbag deployment.
The University of Wisconsin Why Files site also has an informative page about airbags.
References:
Bell, W.L. "Chemistry of Air Bags," (1990) J. Chem. Ed. 67 (1), p. 61.
Crane, H.R. "The Air Bag: An Exercise in Newton's Laws," (1985) The Physics Teacher, 23, p. 576-578.
Cutler, H. and E. Spector. "Air bags and automobile recycling," (1993) Chemtech,23, p. 54-55.
Insurance Institute for Highway Safety. "Airbag Statistics." 7 October 1998.<
http://www.hwysafety.org/airbags/airbag.htm>.
Madlung, A. "The Chemistry Behind the Air Bag: High Tech in First-Year Chemistry," (1996) J. Chem. Ed., 73 (4), p.
347-348.
Newton's Apple: Teacher's Guides. "Airbags and Collisions." 22 June 1998.
<http://www.ktca.org/newtons/9/airbags.html>.
Acknowledgements:
The authors thank Dewey Holten, Mark Conradi, Michelle Gilbertson, Jody Proctor and Carolyn Herman for many
helpful suggestions in the writing of this tutorial.
The development of this tutorial was supported by a grant from the Howard Hughes Medical Institute, through the
Undergraduate Biological Sciences Education program, Grant HHMI# 71199-502008 to Washington University.
Copyright 1998, Washington University, All Rights Reserved.
Revised October, 2000.
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