Why can a moving object (train or car) not simply stop? Why do they always "fall backwards" after the stopped?

Answer 1

When your tires stop your cars body still has a bit of momentom and flexes the suspension (shocks and springs) a little bit. That jerk that you feel is the suspension returning to normal placement. Basically tires stop body still travels forward and suspension yanks it back. Thats why when you have to lock up your tires and stop really hard for some slow grandpa that cut you off the jerk or backward motion is that much harder. Ever noticed that? When you come to that sudden of a stop the momentum of your car compared to the tires is a lot greater. Well thats what I would think anyway. Good luck, I hope this helped.

Answer 2

Many railroad freight cars have a "sliding sill" draft gear or "end of car cushioning device".

These, as the name indicates, are spring loaded devices that reduce the energy of any slack action that travels through the train to help prevent damage to lading. If a train has stopped on level terrain, with automatic air and slack bunched, then when the air brakes are released, the springs will move the cars in the opposite direction. This is, of course, "spring slack".

The same is true if the cars are stopped with the slack bunched using only engine brakes, but the run out of spring slack occurs at the time the train stops, as opposed to when the brakes are released.

This is why someone, when, and only when they MUST cross the tracks near standing equipment, should allow for 50' distance from the end of the last car so it doesn't roll back and get 'cha! It may make no noise so never turn your back to a car either. Never, under any circumstances put yourself between equipment that is not coupled, or you may get "coupled up". You really don't want to hear what this does to a persons body. Just take my word for it.

Answer 3

The potential energy stored in the suspension is released when the object stops decelerating. The same thing happens at the quantum level for less flexible objects you just can't see it.

Answer 4

gravitational pull, the force of the moving object stopping combined with it's weight cause a slight backward movement upon stopping, also is the line perfectly flat?