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Ever wonder how seat belts work to save your life in a crash?

Well buckle up! This video takes you through the inner mechanical workings of the seat belt mechanism, its various functions and internal components.

The three point seat belt is common on most modern passenger vehicles. Normally unlocked, seat belts give the user sufficient freedom to move around while riding in a car.

However when the vehicle undergoes heavy braking or collides with another object, the seat belts lock - and in some cases retract, pulling the occupant away from smacking their face on the dashboard causing injury.

The seat belts also sense when a vehicle is accelerating hard, on an incline, as well as stop if pulled out too far, as well as sense quick sharp tugs on the seat belt and lock it in place.

A cam gear inside controls how much seat belt webbing can be extracted without locking. A gravity ball inside a plastic casing senses the incline of the vehicle under acceleration or braking. A centrifugal ratchet engages when the seat belt is tugged on rapidly. Finally a small tooth engages to lock the seat belt when all of the webbing material has been extracted.

The front seats are a bit different, as they come with pretensioners. Working with the SRS airbag system, the pretensioners will wind up any slack in the seat belt webbing during a collision. This will hold the occupant away from hitting the dashboard and prevent injury.

Seat belt pretensioners contain an explosive because it has to react very quickly during the collision. The explosive pushes a piston that's attached to a wire. The wire is reeled around the seat belt retractor, and thus winds up the slack when fired.

The seat belts in this video were removed from a 2001 Toyota Corolla, and completely taken apart and detonated to explain what's inside and how it works.

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