Quote:
Originally Posted by irish2
Crashing a car into an immovable object at 40km/h, is the same as two identical cars crashing head on at 40km/h. There is no combined speed, you decelerate from 40km/h - 0km/h.
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Two cars, each travelling at 40kph, colliding head-on, IS a combined closing speed of 80kph.
Obviously, if the two cars are identical, then the energy & momentum is equally "absorbed" by both cars, and as you say each car will decelerate from 40 to 0. Hence why it is roughly equivalent to the single car hitting an immovable wall. (Which is what I said.)
However, if somebody in a small car travelling at 40kph, collides head on with a road-train also travelling at 40kph, they will in fact decelerate from 40 to -40, ie -80kph total.
The problem with this test, is that it assumes the test car is "average" (and obviously is being tested against an identical average car.)
What they SHOULD do, is actually create an "average" test vehicle, and stage an actual collision with both vehicles travelling at the same speed.
Not only is their test inaccurate in regards to smaller than average cars, it may well in fact be biased in favour of lightly constructed vehicles.