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Originally Posted by XCXDBABF
Agreed! The collision is not instant, it takes time.
Car drives into wall at 100km/h and stops. Forces required? Over what period of time? Both car and wall experience the same force.
Two men decide to go bungee jumping. The first selects a elastic rope (bungee cord) as his method of connection to the mounting point, the other selects a steel wire rope. Both men reach terminal velocity during their fall and reach a stop at the end of their fall. Neither connection method to the mounting point fails and neither man hits the ground, yet while one man has an exhilarating experience, the other dies. Why?
Forces required? Over what period of time?
Car drives into wall at 100km/h and stops.
Car traveling at 100km/h drives into another car exactly the same traveling in the opposite direction at 100km/h and both stop.
There is no doubt that the wall and the car exert the same force over the same period of time on each other.
The two cars involved in the two car collision exert the same force over the same period of time on each other.
BUT - Do the car hitting the wall and the car hitting the other car apply the same force over the same period of time during their independent collisions?
This is why you need to consider the relative velocity.
I know I said it before, but now I am finished.
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Yes they do.
And you miss the point of the relative velocity because in the 2 ball at 20 situation the impact is travelling at a different velocity to the one ball at 40 and the wall.
The wall is that situation is traveling at 20km/h relative to the impact in the first case and as the wall does not change its state it must continue at 20km/h relative to the first case.
THAT IS WHY THEY ARE DIFFERENT
In one case 2 objects change state.
In the other case only one object changes state.