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An airbag is a safety device that protects the passenger in the event of a collision, by restricting their movement and inducing a slow reduction of the body’s momentum as opposed to coming to an abrupt halt. The greatest thing about an air bag is that along with the seat belt, it can reduce death in a collision by about 30%.

How does an airbag help in safety?
During a collision, the body of the passenger would continue to move forward, even if the vehicle has come to a sudden halt. This is because of the momentum carried by the body. So, in a collision, the upper part of the body hits the steering wheel or the dashboard hard causing fatal injuries or death. In high speeds, the passenger’s head even collides with the wind shield. This is extremely dangerous.

An airbag prevents the passenger from being thrown toward the dashboard. It also slows down the process of the body’s motion coming to zero velocity.

How is an airbag deployed?
There are collision detectors installed along with the airbags. When a collision happens, these sensors detect it, and send the signal to the airbag. In the airbag, this signal triggers a reaction between sodium azide and potassium nitrate. This reaction releases nitrogen gas which inflates the air bag. All of this happens under a fraction of a second and after the deployment, the nitrogen gas escapes through holes in the airbag to cause deflation in order for the passenger to move.

Different types of airbags

Frontal airbag
Frontal air bags are designed to prevent occupants from anything that is at the front portion of the car, like dashboard, steering wheel or wind shield. Since 1998, frontal airbags have been a standard in all the vehicles. Frontal airbags do not eliminate the need for seat belts. And they also do not protect the passenger in rear collision or a rollover. The amount of protection an airbag can offer depends a lot on whether the seat belt is fastened or not. Seat belts keep the passenger in the proper position to ensure protection by the airbag. An important thing to keep in mind is, if the seat belt is not on while in a collision, airbags can cause fatal injuries to the passenger.

Side torso airbag
This protects the passenger from injury to the ribcage and the pelvis. This airbags deploys in between the passenger and the door. Special designs are being included recently and these protect the passenger even in a roll over crash.

Side curtain airbag
The side curtain airbag deploys from the roof and protects the passenger from rollover injuries. Roll sensing side curtain bags are usually used in SUVs and pickup trucks because they are prone to rollovers. But in case the driver in taking the vehicle off road, he can disable the feature.

Knee airbag
This airbag is meant to protect the knees since the knee too is highly exposed while in a collision. These airbags deploy just below the steering wheel. The knee airbag has been increasingly used in cars since 2000.

Seat cushion airbag
The seat cushion airbag prevents the pelvis from diving below the lap belt in a collision.

Center airbag
This is meant to protect the rear passengers from head injuries. It deploys from the rear center seat. In 2012, General Motors introduced a center airbag which deploys from the driver seat.

Seat belt airbag
This is actually a seat belt that can be used like any other seat belt. But in a collision, the seat belt inflates and offers extra protection.

Pedestrian airbag
Pedestrian airbags are different in that they protect the pedestrian as opposed to the passengers. It was introduced in Volvo V40 in 2012 and it deploys from the car bonnet, so that the impact of the car on the pedestrian’s body is reduced.
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Did you ever think how the wheels of your car initiated to move ahead. The rotational force is passed from the transmission to the differential. The drive-shaft also known as a propeller shaft or cardan shaft is a device that transfers rotational force from the transmission system to the differential. Technically, a drive-shaft transfers torque and rotation to parts of the vehicle that are far from the transmission system. In automobiles, it is a longitudinal shaft from an engine/transmission to the other end of the vehicle before it goes to the wheels. Physically, it is tubular in design, with an outside metal housing that protects an interior metal cylinder.

Parts of a differential:

Flange: The flange is a collar like structure that fastens the drive-shaft to the pinion gear.

Pinion gear: This is just a normal gear and rides on the larger ring gear at a 90 degree angle.

Side gears: Side gears receive the rotation directly from the ring gear and transfer it to the axle.

Ring Gear: The biggest gear in the differential. This is the gear that receives the rotation from the drive-shaft.

Left and right axle shaft: Axle shafts on both the sides of the vehicle.

Spider Gears: Spider gears hold both the axles intact and allow the two axles to rotate at two different speeds.

Why is a differential needed?
The need for a differential arises due to a single, simple reason. While the vehicle turns towards the right or left, the wheels don’t rotate in the same speed. While taking a turn, the distance traveled by the front wheels is always a little more than the rear wheels. Since distance is directly proportional to the speed, the wheels spin at different speeds.

Now, if all the wheels had been fixed in order to spin at the same speed, at turns, the slow-spinning wheels have to drag on the ground, since their necessity to undergo spinning is less. If the vehicle is making a right turn, the order of speeds in each wheel is Front Left>Front Right>Rear Left>Rear Right. In case of the absence of differentials, in hard surfaces such as tar, the drag faced by the wheel that undergoes less spin is more intense. This induces wear and tear on the tire and driving on such conditions is also difficult.

The drive-shaft carries the rotating motion from the engine crankshaft to the differential. At the differential, the Ring gear along with the side gear and pinion gear breaks the flow of rotational motion in between so that, the wheels can rotate at different speeds while the differential receives a single speed of rotation.
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