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Why use safety
belts?
Frontal collisions and the law of physics
Frontal
crashes
create very strong forces for peo-
ple riding
in
vehicles
.
Fig. 137
Unbelted occupants
in
a vehicle
heading
for a wall
Fig.
138 The
vehicle crashes into th
e
wall
CD
~
±
<t
ID
The
physical principles
are simple.
Both the
vehi-
cle and the passengers possess energy which var-
ies
with vehicle speed and body weight
.
Engi-
neers call this energy "kinetic energy."
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
veh icle
are
not us-
ing
safety
belts
~
fig. 13
7, they
will keep
moving
at
the same speed
the vehicle
was moving
just
before the crash,
until
something stops them
-
here,
the wall
~
fig. 138.
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
Safety
belts
(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 collision
they will also
keep
moving forward at
the
speed
their vehicle was travelling
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 collisions.
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.
139
A driver
not wearing
a
safet
y belt is viol
entl
y
thrown forwa rd
Fig. 140
A rear passenger
not
wear ing a safety belt w ill fly
fo rward and strike t he
driver
Unbelted
occupants are
not
able to resist the tre-
mendous forces of
impact by holding
tight or
bracing
themselves
.
Without the benefit of safe-
ty restraint systems, the
unrestrained
occupant
will slam violently
into
the steering wheel,
in-
strument panel, windshield, or whatever else is
in the way
~
fig. 139
.
This
impact
with the veh i-
cle
inter ior
has
a
ll
the energy they
had just
before
the
crash.
.,.
125
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