Fig. 104 The vehicle
crashes into the wall.
The physical principles are simple. Both the vehicle and the passen-
gers possess energy which varies with vehicle speed and body
weight . Engineers 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 occupants in this vehicle are not using safety belts
~
page 128, fig . 103, they will keep moving at the same speed the
vehicle was moving just before the crash, until something stops
them - here, the wall ~ fig. 104.
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
(2,000 lbs, or 1,000 kg) or more . At higher speeds , these forces are
even greater.
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. •
Safety first
Safety belts
What happens to occupants not wearing
safety belt s?
In crashes unbelted occupants cannot stop themselves
from flying forward and being injured or killed. Always
wear your safety belts!
Fig. 105 A driver not
wearing a safety belt is
violently thrown
forward
Fig. 106 A rear
passenger not wearing
a safety belt will fly
forward and strike the
driver
Unbelted occupants are not able to resist the tremendous forces of
impact by holding tight or bracing themselves. Without the benefit
of safety restraint systems, the unrestrained occupant will slam
violently into the steering wheel , instrument panel , windshield , or
whatever else is in the way ~ fig. 105. This impact with the vehicle
interior has all th e energy they had just before the crash.
Never rely on airbags alone for protection. Even when they deploy,
airbags provide only additional protection. Airbags are not
91>
Vehicle care
I I
irechnical data
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