146 S a fet y belt s
- 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. 156 Unbe lted occupants in a ve hicle heading for a
wall
Fig. 157 The vehicle crashes into the wall
The physical principles are simple. Both the
vehicle and the passengers possess energy
which varies with veh icle speed and body
weight . Engineers call this energy "kinetic en-
ergy."
The higher the speed of the vehicle and the
greater the vehicle's we ight, the more energy
that has to be "absorbed" in the crash .
Vehicle speed is the most sign ificant factor.
If
the speed doubles from 15 to 30 mph (25 to
50 km/h), the energy increases 4 t imes!
Because the passengers of this veh icle are not
using safety belts¢
fig. 156, they will keep
moving at the same speed the vehicle was
moving just before the crash, unt il something
stops them - here, the wall ¢
fig. 157 .
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
highe r.
Peop le 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 veh icle was t ravell ing just before
the crash . Of course, the laws of physics don't
just app ly t o frontal collisions, t hey 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. 158 A driver not wea ring a saf et y belt is violently
thrown fo rwa rd
Fig. 15 9 A rear passe nge r not wea ring a safety be lt
will fly fo rward a nd strike th e dr iver
Unbelted occupants are not able to resist the
t remendous forces of impac t by holding tight
or bracing themse lves. Withou t the benefit of
safety restraint systems , the unrestrained
ll-
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