We have had another of those wrecks that make those of us (most of us) who like people and trains very sad. It happened in Seville. Fla. on Thursday, the 18th of April, and the NY Times had articles on the 19th and 20th, but I think it was in one of the Maine papers that I saw the photograph of the cars all askew, something like this:

            /|
           / |  /\    /|
     -----/--|-/--\--/-|--/-----
             |/    \/  | /
                       |/

We have all seen that picture too many times, and this time it got me to thinking about elevators and the elevator effect.

My first thought was that that looks like what you would get if you were to take a chain made of long links (like the ones we had on swings when I was a boy), hold it vertically at both ends, and then let go at the top. It would buckle and fall in a heap, sort of like that diagram suitably rotated.

Then on Saturday I read about how the engineer had seen trouble ahead and had "tried to bring the train to an abrupt emergency stop", and that clinched it. According to the elevator effect, we would be weightless for a while in a free-falling elevator. Said differently, the downward force of gravity is cancelled out if we are falling with the acceleration of gravity, and said yet again, a downward acceleration decreases the effect of gravity and an upward acceleration increases the effect of gravity. Take away the gravity, and an acceleration in some direction (upward) causes effects that act like a positive gravity opposed to it (downward). A deceleration (upward) causes effects like a positive gravity aligned with it (upward).

Now turn it all on it's side, where there is no gravity in the horizontal directions, and say it again: an acceleration in some direction (northward) feels like a positive gravity (southward) and a deceleration (northward) feels like a positive gravity (northward). I can't imagine anyone has not personally felt that - in cars, on bikes, rollerblades, what-have-you. (Maybe the other Fred would like to write one about that.)

Back to trains now: in whatever direction we are headed (call it northward), acceleration is good - the train is anchored by the engine, which is heavy, and in the effective gravity (positive, directed southward) it is hanging from its "upward end" - nice and stable. Deceleration, on the other hand, is baad (especially the rapid deceleration of faast trains) - in the reversed effective gravity (positive, directed northward) the train is anchored at its "downward end", and it wants to buckle.

So, what to do? Putting the engine behind won't work because that makes acceleration and uphill travel in general really bad. Brakes in the rear? Well yes, and I suppose that setting the breaks was one of the functions of whoever manned the caboose. (Seen one lately, other than the ones we sometimes see gracing the yards of my northcountry friends?) It would have to be a pretty heavy caboose though, so why not just have two engines - anchors at both ends of the ship.

Hauling a second engine along wouldn't be hauling a dead weight if it was working too. All the lead engine feels is the tension from what lies behind, so two smaller engines would work more or less like one larger one. Rigging things so the cars between are under tension, accelerating or decelerating, shouldn't be all that difficult.

And why isn't something like that done? Well there quite a few possibilities:

• Maybe I'm just crazy, and physics has nothing to do with trainwrecks (just kidding).
• Maybe that was just a bad idea: a train that can't buckle might roll, and that might be even worse!
• Maybe it was known what to do in the 19th century, but whoever makes decisions for AMTRAK has forgotten about it.
• Maybe it's still well known, but AMTRAK can't afford do do anything about it.

Well I hope it's not that last one, and I wonder: Who works on this? Who knows more about it than this? Anybody out there know more?

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