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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. 146
Unbe lted occupants in
a
veh icle heading for a wall
Fig. 147 The vehicle crashes into the wall
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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 SO
km/h), the energy increases 4 times!
Because the passengers of this veh icle are not us-
ing safety belts ¢ fig. 146, they will keep moving
at the same speed the vehicle was moving just
before the crash, until something stops them -
here, the wall ¢ fig . 147.
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 SO 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 collis ion
they will also keep moving fo rward 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. 148 A driver not wea ring a safe ty belt is violent ly
throw n forward
Fig. 149
A rea r passe nge r not wea ring a safe ty belt will fly
forwa rd and strike the 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 , o r whatever else is
in the way ¢ fig. 148. This impact with the vehi-
cle interior has all the energy they had just be-
fore the crash .
..,.
135
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