May 12, 2018
RAY: Here’s a puzzler of yesteryear.
Imagine, if you will, a long freight train. Like the kind you see out West with a couple of hundred cars getting ready to leave the train yard. The engineer opens the throttle and the train starts to pull away from the yard. Then they realize that the caboose has a problem. The brake is frozen on one of the wheels of the caboose.
TOM: How would they know?
RAY: Because the wheel is being dragged and there's sparks and smoke. And someone standing there says, "Stop the train." So, they manage to signal to the engineer, to stop the train. Well, they can't fix it, so they just cut the caboose loose. They remove it and they give him the go ahead. They wave him. You know. Go ahead. He gives it the throttle. The train doesn't move.
RAY: He gives it more throttle, it doesn't move. He gives it more and what's happening is the train isn't moving, but his wheels are spinning. There's nothing wrong with any of the remaining cars and there's nothing wrong with the engine, but there is something wrong with the engineer.
The question is what's wrong with this picture?
RAY: When a locomotive is pulling cars, each car is attached to the one in front of it and behind it by a coupling, but the couplings aren't rigid. They're, in fact, sloppy.
So when a long freight train pulls out of a yard, before it takes off, it will frequently back up to compress all the couplings and then when it takes off, one car at a time begins to move and it's quite a while, in fact, before the caboose begins to move.
RAY: But in this situation, the train was stopped. He did that backing up thing. I failed to mention that in the statement of the puzzler.
TOM: Another form of obfuscation and nicely done I thought.
RAY: The train is halted because the brake is stuck and because it's stuck, the caboose is in a sense pulling the train from the other end. So, now all the couplings are all stretched out. They remove the caboose, but the guy doesn't back up.
So he's going to try to move the last car while he's trying to move the first car and the train is just too heavy and he doesn't have enough friction between the wheels on the track --
TOM: So, a train can't really pull from a dead stop all the cars that you see behind it sometimes.
RAY: If it's long enough, it can't do it.
TOM: So, the little engine that couldn't.