Audi A6 Typ 4G: Why use safety belts?

Frontal collisions and the law of physics

Frontal crashes create very strong forces for people riding in vehicles.

Fig. 143 Unbelted occupants in a vehicle heading for a wall

Fig. 144 The vehicle crashes into the wall

The physical principles are simple. Both the vehicle and the passengers possess energy which varies with vehicle speed and body weight. Engineers call this energy " kinetic energy." The higher the speed of the vehicle and the greater the vehicle's weight, the more energy that has to be "absorbed" in the crash.

Vehicle speed is the most significant factor. If the speed doubles from 15 to 30 mph (25 to 50 km/h), the energy increases 4 times! Because the passengers of this vehicle are not using safety belts fig. 143, they will keep moving at the same speed the vehicle was moving just before the crash, until something stops them - here, the wall fig. 144.

The same principles apply to people sitting in a vehicle that is involved in a frontal collision. Even at city speeds of 20 to 30 mph (30 to 50 km/h), the forces acting on the body can reach one ton (2,000 lbs, or 1,000 kg) or more. At greater speeds, these forces are even higher.

People who do not use safety belts are also not attached to their vehicle. In a frontal collision they will also keep moving forward at the speed their vehicle was travelling just before the crash.

Of course, the laws of physics don't just apply to frontal collisions, they determine what happens in all kinds of accidents and collisions.

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