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13 2
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. 11 2 Unbe lted occupants in a ve hicle heading for a
wall
Fig. 1 13 The vehicle cra shes into t he wall
The physical principles are simp le. Both the
vehicle and the passengers possess energy
which varies with veh icle speed and body
weight . Engineers call this energy "kinetic en-
e rgy."
The higher the speed of the vehicle and the
g reater 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
c::;,
fig. 112, 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 . 113 .
The same principles apply to people s itting 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-
s io n 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. 11 4 A driver not wea ring a saf et y belt is viol ent ly
thrown fo rwa rd
Fig. 11 5 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 a re not able to resist the
t remendous forces of impac t by ho lding tight
or bracing themse lves. Withou t the benefit of
safety restraint systems , the unrestrained
ll-
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