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Safety
belts
Why use safety
belts?
Frontal collisions and the law of physics
Frontal crashes create very strong forces for peo-
ple riding in vehicles
.
Fig. 122
Unbelted occupants
in
a vehicle
headi
ng
for
a wall
Fig. 123
The
vehicle crashes
into
the wall
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 vehicle are not
us-
ing
safety belts
~
fig.
122, they
will keep
moving
at
the same speed the
vehicle
was moving
just
before the crash, unti
l
something stops them -
here, the wall
~
fig
.
123.
The same principles apply to
people sitt ing
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
122
(2,000 lbs.
or
1,000
kg)
o
r
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. 124
A
driver
not wea ring a safety belt is violen
tl
y
thrown
forward
Fig. 125
A
rea
r
passe
nge
r
not wear ing a safety
belt
will fly
forward an
d
str ike the
driver
Unbelted
occupants a re not able to res ist
the
tre
-
mendous forces of impact
by
holding tight or
bracing themselves. Without
the benefit of safe-
ty restraint
systems, the
un
restra ined
occupant
will slam violently into
t
he
steering
wheel
,
in-
strument pane l, windshield, or whatever e lse is
in
the way
~
fig
.
124.
This impact with the vehi
-
cle interior
has
a
ll
the energy they had just be-
fore the crash.
liJJ,-
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