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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. 144
Unbelted occupants in a vehicle headi ng for a wall
Fig. 145
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 t imes!
Because the passengers of this vehicle are not us-
ing safety belts ~ fig. 144, 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 . 145.
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
128
(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. 146
A driver not wea ring a safety belt is violentl y
thrown forward
Fig. 147 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 . 146. This impact with the vehi -
cle interior has a ll the energy they had just be-
fore the crash.
liJJ,-
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