Seat Belt is a safety device installed in the car which protects the occupants by restricting their undesirable forward movement during the events of a collision. It is also known as ‘Safety belt’.
During the mid of twentieth century, experts in the auto-industry realized that when a car meets an accident, the passengers in the car are injured more because they strike with the internal parts of the car like steering wheel, dashboard etc. This fact led to the development of a device which would avoid the forward movement of passengers during events of sudden stoppage or crash, which is nothing but a seat belt.
In terms of Physics, this phenomenon is nothing but inertia. When a car moves at a certain speed, the passengers in the car also move with the same speed. Thus, making this entire system (i.e. car and passengers) act as a single unit. However, when the car comes to a halt suddenly, the inertia of the passengers i.e. the tendency to continue the state of motion, makes them move with their original speed which eventually results in a passenger striking the internal parts of the vehicle like a dashboard. Seat belt, in such a situation, applies the opposite force on the passenger thus preventing him/her from colliding.
Advantages of using a seat belt:
- Reduces the dangers of secondary impacts
- Keeps the passengers seated in the proper position so that airbag can work with maximum efficiency
- Protects occupants during events like rollover
The seatbelts employed in modern vehicles are generally ‘Three-point’ type. They are called so because they are anchored at three points. The picture below depicts a typical three-point type seat belt:
These seat belts comprise a lap belt and a shoulder belt. The vehicle body supports it at three different fixed points. The main advantage of using the three-point belt is that it distributes the stopping force equally on the firm parts of the body like shoulders, chest, and pelvis. Thus, it provides better support compared to a ‘two-point’ belt used previously.
Volvo first introduced the concept of ‘Three-point’ belt in 1959. Volvo 122S (also known as Volvo Amazon) is the first production vehicle to have three-point seat belt as a standard fitment.