gonadman

I believe the physics the govern this situation is Newton's three laws of motion:
1 An object at rest tends to stay at rest unless acted upon by another force
2 An object in motion tends to stay in motion unless acted upon by another force
3 For every action there is an equal and opposite reaction

Of course this is the simplicity behind what KnifeMissl explained so eloquently in his first post. The force is acceleration, which affects everything within the car, dependant upon its mass(Force= mass*acceleration, right?)

Once the car reached a steady cruising speed, all objects within that car will remain in constant motion relative to objects outside the car, but without motion relative to other objects within the car that are travelling at the same speed. Thus we do not feel wind on our face at 80mph within the car, and others on the train appear as normal to fellow passengers even though they are hurtling along at 85mph.

Of course all this changes dramatically when that dog runs in front of your car, and you slam on the brakes. You can be sure that fly will crash into your front windshield along with everything else in the car, with a force that is proportional to its weight. The objects in the car, due to the second law, continue in motion even though the car is slowing due to brake friction. The ultimate force stopping this motion, in this scenario, is the windshield.

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For me there is only the traveling on paths that have heart, on any path that may have heart. There I travel, and the only worthwhile challenge is to traverse its full length. And there I travel, looking, looking, ...breathlessly.
-Carlos Castaneda