The physical principles of a frontal collision are simple. Both the moving vehicle and the passenger
possess energy
⇒
fig. 46
, 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 has to be
“absorbed” in a crash.
Vehicle speed is the most significant factor. If your speed doubles (for example, from 15 mph to
30 mph – 25 km/h to 50 km/h), the energy increases 4 times!
Because the occupants of the vehicle in the above example are not using safety belts, they are not
“attached” to the vehicle. In a frontal collision, they will keep moving at the same speed the vehicle
was moving just before the crash, until something stops them - here, the inside of the passenger
compartment. Because the occupants of the vehicle in the example are not wearing safety belts, their
entire kinetic energy will be absorbed by impact with the wall
⇒
fig. 47
.
The same principles apply to people in a vehicle that is in a frontal collision on the highway. Even at
city speeds of 20–30 mph (30–50 km/h), the forces acting on the body can reach one ton (2,000 lbs or
1,000 kg) or more. At greater speeds, these forces are even higher.
Of course, the laws of physics don't apply just to frontal collisions; they determine what happens in all
kinds of accidents and collisions.
What happens to passengers not wearing a safety belt
Fig. 48
The unbelted driver is thrown forward.
Fig. 49
Unbelted passengers in the rear seats are thrown forward on top of the belted driver.
