A bag that fills with air to protect a driver or passenger when a vehicle crashes.
Who invented airbags?
If you search around online, you'll find quite a few different people are credited with inventing airbags.
Who thought of them first? It appears to have been John W. Hetrick of Newport, Pennsylvania, who
came up with the idea after an accident in which he swerved his car off the road into a ditch to avoid hitting a rock,
almost throwing his daughter through the windshield. Hetrick filed his patent for a Safety cushion assembly for automotive vehicles
on August 5, 1952 (it was granted as US Patent #2,649,311 on August 18,
1953). Although a German inventor named Walter Linderer filed an airbag
patent several months before Hetrick, it was granted
after Hetrick's, and it seems likely that the two men came up with the
same idea independently. Many other inventors have built on the idea
since then, notably Allen K. Breed
(1927–2000), who developed a variety of different ways of triggering the
explosion of gas inside an airbag just before the impact of a crash.
According to
Breed's New York Times obituary,
he made his first airbag design in 1968, and filed numerous patents for
improvements, helping to turn Breed Corporation into one of the world's
largest suppliers of car safety systems.
Objects
in a car have mass, speed and direction. If the object, such as a
person, is not secured
in the car they will continue moving
in the same direction (forward) with the same speed (the speed the car
was going) when
the car abruptly stops until a force
acts on them.
Every object has momentum. Momentum is the product of a passenger's mass
and velocity ( speed with a
direction). In order to stop the passenger's momentum they have to be
acted on
by a force. In some situations the
passenger hits into the dashboard or windshield which acts as a force
stopping them but
injuring them at the same time.
An airbag provides a force over time. This is known as impulse. The more time the force has
to act on the passenger to slow them down, the less damage caused to the passenger
There is a restricted amount of time that the airbag has to act between when the car hits
the other object and the passenger hits the steering wheel.
- About 15 to 20 milliseconds after the collision occurs the crash sensors decide whether
or not the collision is serious enough to inflate the airbag (usually 6 - 10 km/h).
- If the crash sensors decide to inflate the airbag it will be deflated at about 25 milliseconds
after the crash.
- It takes about 20 milliseconds to inflate the airbag for the person to land into.
- Around 60 milliseconds the person has made contact with the airbag and the airbag now
starts to deflate.
- The passenger continues to be acted on by the airbag as it is in the deflation process which
takes about 35 to 40 milliseconds.
It is still necessary to wear a seat belt although all automobiles must be equipped with an airbag
because of a few reasons:
1)
The crash sensors do not signal for the airbag to inflate unless the
vehicle is moving at least
6 km/h. Damage can still occur to
the passenger if the collision is of a slower speed. This is were the
seat belt plays an
important role.
2) The airbag located in the steering wheel does not help the passenger in a collision where
another car hits them side on.
3) When the car the passenger is in is backing up and collides the its rear end with another
object the airbag does not help.
With
today's technology other airbags are being introduced in addition to
the steering
wheel airbag and the passenger
airbag. Such airbags that are being introduced are side airbags and head
airbags.
The trouble with momentum
Like everything else in the world,
car crashes are controlled by the laws of physics—and, more specifically, the
laws of motion. Anything that
moves has mass (very loosely speaking, this means how much
"stuff" an object contains and it's closely related to how heavy it
feels) and velocity
(loosely, this is the same thing as speed, but strictly it means
speed in a certain direction). Anything that has mass and velocity has
kinetic energy, and the heavier your car and
the faster you're going,
the more kinetic energy it has. That's fine until you suddenly want
to stop—or until you crash into something. Then all the energy has
to go somewhere. Even though cars are designed to crumple up and
absorb impacts, their energy still poses a major risk to the
driver and passengers.
The trouble is, people inside a
moving car have mass and velocity too and, even if the car stops,
they'll tend to keep on going. It's a basic law of physics (known as
Newton's first law of motion, after brilliant English physicist Sir Isaac
Newton who first stated it) that things that are moving tend to keep
on moving until something (a force of some kind) stops them. Cars
have had seat belts for decades, but they're a fairly crude form of
protection. The biggest problem is that they restrain only your body.
Your head weighs a surprising 3–6kg (6–12lb)—as much as several bags of
sugar— and isn't restrained at all. So even if your body is fastened
tight, the same basic law of
physics says your head will keep on going and smash into the
steering wheel or the glass windshield (windscreen).
That's where airbags come
Photo: Sir Isaac Newton (1642–1727) formulated
three basic laws
describing how forces work.
Picture courtesy of US Library of Congress.
How airbags help
An airbag is more correctly known
as a supplementary restraint system (SRS) or supplementary
inflatable
restraint (SIR). The word "supplementary" here means that the
airbag is designed to help the seatbelts protect you rather than
replace them (relying on an airbag to protect you without fastening
your seatbelt is extremely dangerous).
The basic idea is that the airbag
inflates as soon as the car starts to slow down in an accident and
deflates as your head presses against it. That's important: if the bag
didn't
deflate, your head would just bounce back off it and you'd be no better
off.
How airbags work
- When a car hits something, it starts to decelerate (lose speed) very rapidly.
- An accelerometer (electronic chip that measures acceleration or force) detects the change of speed.
- If the deceleration is great enough, the accelerometer triggers the airbag circuit. Normal braking doesn't generate enough force to do this.
- The airbag circuit passes an electric current through a heating element (a bit like one of the wires in a toaster).
- The heating element ignites a chemical explosive. Older airbags used sodium azide as their explosive; newer ones use different chemicals.
- As the explosive burns, it generates a massive amount of harmless gas (typically either nitrogen or argon) that floods into a nylon bag packed behind the steering wheel.
- As
the bag expands, it blows the plastic cover off the steering wheel and
inflates in front of the driver. The bag is coated with a chalky
substance such as talcum powder to help it unwrap smoothly.
- The driver (moving forward because of the impact) pushes against the
bag. This makes the bag deflate as the gas it contains escapes through
small holes around its edges. By the time the car stops, the bag should
have completely deflated.
uses : In cars specially
related link : https://www.youtube.com/watch?v=KZOdljBtoeo
