Safety
Head-on collisions and the laws of
physics Fig. 8
A driver not wearing a seat belt is thrown
f orw ar
d viol ently. Fig. 9
The unbelted passenger in the rear seat
is thr own f
orwar
d viol ently, hitting the driv
er
who is wearing a seat belt. The effects of the laws of physics in the case
of a head-on collision ar
e easy t
o expl
ain: the
moment a v ehicl
e st
arts moving, a type of en- ergy called “kinetic energy” starts acting on
both the vehicle and its passengers.
The amount of “kinetic energy” depends onthe speed of the vehicle and on the weight of
the v
ehicle and of its passengers. The higher
they are, the more energy there is to be “ab-
sorbed” in the event of an accident.
The most significant factor, however, is the
speed of the vehicle. If the speed doubles
from 25 km/h (15 mph) to 50 km/h (30 mph),
for example, the corresponding kinetic ener-
gy is multiplied by four.
Given that the passengers of the vehicle in
our example do not have their seat belts fas-
tened, in the event of a collision the entire
amount of the passengers
