Assume you can hook every locomotive and car Union Pacific owns up into a single gigantic freight train. Safety and laws aside, would it work?
In: Physics
You, five year old, can drag your red ryder sled behind you. If you let it go, the sled will come to a stop.
It comes to a stop because of this thing called friction. When two objects slide against each other, they slow down. It takes more energy to keep them moving. If you aren’t there to pull the weight, or more importantly, if you _can’t_ pull the weight, the sled would stay put.
Weight makes friction more and more of a problem. If you put some rocks in your red ryder, the weight that you’re pulling will be a lot more. You’ll pull more slowly the more weight you add, and with too much weight, you won’t be able to overcome friction and the sled can’t move at all.
A train’s engine car at the front is just like you, pulling your red ryders. A train just has a bigger engine, and can pull heavier things at faster speeds. But, just like you, trains have their limits. An engine can only pull so much freight. The more cars you add, and the more things you put in those cars, the heavier the train gets. That means it will get slower and slower, until it can’t move at all.
Now, if I can go on a tangent for a bit, the solution to this problem was successfully implemented some 70 years ago… by Walt Disney Imagineering, then known as WED Enterprises. Walt and his engineering team put together a propulsion system where the _track_ was what would provide the energy, not an engine car. This was the peoplemover system, but you might better understand it exemplified as the haunted mansion doom buggies. Each buggy is its own, self-propelled carriage, pushed and pulled along the track by a series of magnets placed at regular intervals. This isn’t a _train_ if you define a train as a single engine pulling a series of cars. But it _is_ a constant, infinite line of cars moving along a track.
There are a few cities around the world who have used peoplemover tech in their public transit system, but to this day it’s pretty rare. One reason for this is that theme park rides are non-essential. With a conventional train, the tracks are simple and the trains are complex. That means trains need repairs more often than tracks do. If you need your trains to run as much as possible, the tracks need to be reliable.
If a train or its cars need repairs, you can take that one train off the tracks without interrupting the path of other trains that use that track. When your track has a problem, and your track is filled with cars end-to-end, the entire route is blocked until the track can be fixed.
That’s not the only concern, either, but, this is already waay more than you asked for, so I’ll leave it at that. The answer is that, no, you’d have to have much, much stronger engines to pull trillions of tons worth of freight as one singular train. There are other systems that exist to get a constant stream of cars moving infinitely along a track, but those aren’t technically trains, and come with their own set of problems. Great for theme parks, though!
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