- Failure to pay attention to the warning
light that come on, could lead to person-
al injury.
Why safety belts?
Frontal collisions and the law of physics
Frontal crashes create very strong forces for
people riding in vehicles .
Fig. 14 7 Unbe lted occupants in a vehicle head ing for a
wall
Fig. 14 8 The vehicle cras hes into the wall
The physical principles are simple. Both the
vehicle and the passengers possess energy
which varies w ith 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
SO km/h), the energy increases 4 t imes!
Because the passengers of th is vehicle are not
using safety belts¢
fig. 147, they will keep
moving at the same speed the vehicle was
moving just befo re the crash, unt il something
stops them - here, the wall ¢
fig. 148 .
Safety belts 139
The same principles apply to people sitting in
a vehicle that is involved in a frontal coll ision.
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 fo rces are even
highe r.
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 travel li ng just before
the crash. Of course, the laws of physics don't
just apply to frontal collisions, t hey determine
what happens in all kinds of accident s 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. 14 9 A driver not wea ring a safety be lt is violently
th rown forwa rd
Fig. 150 A rear passenger not wearing a safety belt
will fly forward a nd strike the driver
Unbelted occupants are not able to resist t he
tremendous forces of impact by hold ing tight
or bracing themse lves. Without the benefit of
safety restraint systems, the unrestra ined .,..
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