The Loose Caboose

May 10, 2014

RAY: Imagine, if you will, a long freight train. It's pulled into the train yard and all the workers get out to go to the bathroom. They get back in and the engineer opens the throttle and the train starts to pull away from the yard, when they realize the caboose has a problem. The brake is frozen on one of the wheels of the caboose. The wheel is being dragged and there's sparks and smoke.

TOM: Yeah.

RAY: And someone standing there says, "Stop the train." So, they manage to signal to the engineer to stop the train. They can't fix it, so they just cut the caboose loose. They remove it and they give him the go ahead. He gives it the throttle. The train doesn't move. He gives it more throttle. It doesn't move.

What's happening is the train isn't moving, but his wheels are spinning. The cars aren't moving. 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.

TOM: Wow. This is good.

RAY: The question is, what's wrong?

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 are, in fact, sloppy. When a long freight train pulls into 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.

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.

TOM: Right.

RAY: They give him the go ahead. He says, "OK. I'll go ahead."

TOM: So, now he's going to pull all 750 cars --

RAY: At once. 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. He doesn't have enough friction between the wheels and the track to accomplish this.

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. So who’s our winner?

TOM: The winner this week is  Rick Johnson from Des Moines, Iowa. Congratulations!

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