138 S a fet y belt s
Why safety belts?
Frontal collisions and the law of physics
Frontal crashes create very strong forces for
people riding in vehicles .
Fig. 14 3 Unbe lted occupa nts in a vehicle heading for a
wall
Fig. 144 The vehicle crashes into t he wall
The physical princip les are simp le. Both the
vehicle and the passengers possess energy
which varies with veh icle speed and body
weight . Engineers call th is 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 doub les 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 be lts ¢
fig. 143, they will keep
moving at the same speed the vehicle was
mov ing just before the crash, unti l something
stops them - here, the wall ¢
fig . 144 .
The same pr inciples 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 .
Peop le who do not use safety belts are also
not at tached to their vehicle. In a frontal colli-
sion they will also keep moving forward at t he
speed their vehicle was travell ing ju st before
the crash. Of course, the laws of physics do n't
just app ly 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 safe ty belts!
Fig. 14 S A driver not wea ring a safety belt is viole ntly
thrown forward
Fig. 146 A rear passe nger not we aring a safety belt
will fly forward and strike t he driver
Unbelted occupants are not able to resist the
t remendous forces of impact by hold ing tight
or bracing themse lves . Without the benefit of
safety restra int systems, the unrestra ined oc-
cupan t will slam violen t ly into the steer ing
whee l, instr ument pane l, windshield, or what-
ever else is in the way r:!>fig . 145 . This impact II>-
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