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130
Safety
belts
Why safety
belts?
Frontal collisions and the law of physics
Frontal crashes create very strong forces for
people riding in vehicles .
Fig. 123
Unbelted occupants in a vehicle heading for a
wall
Fig. 124
The vehicle cras hes into the wall
The physical princip les are simple. Both the
vehicle and the passengers possess energy
which varies with vehicle speed and body
weight . Engineers call this energy ''kinetic en -
ergy ."
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. 123, they will keep
moving at the same speed the vehicle was
moving just before the crash, until something
stops them - here, the wall ¢ fig . 124 .
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 colli-
sion they will also keep moving forward at the
speed their vehicle was travell ing 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 col-
lisions .
What happens to occupants not wearing
safety belts?
In crashes unbelted occupants cannot stop
themselves from flying forward and being in-
jured or killed . Always wear your safety belts!
Fig. 12S
A dr iver not wea ring a safety belt is violen tly
thrown fo rward
Fig. 126
A rear passe nger not we aring a safety belt
will fly fo rward and strike t he driver
Unbelted occupants are not able to resist the
tremendous forces of impact by holding tight
or bracing themse lves . Without the benefit of
safety restraint systems, the unrestra ined oc-
cupant will slam violently into the steering
whee l, instr ument panel, windshield, or what-
ever else is in the way r:!> fig . 125 . This impact
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