Just passed by a train with a hundred or so cargo crates. how do they start? I understand how they continue moving, but how do they overcome the inertia of starting it? It has to be like thousands of tons, and I can’t imagine a bunch of coal being able to start moving that. unless of course it can, in which ELI5
In: Engineering
It only pulls one car at a time. The cars are actually closer together on a stopped train than on a moving one. When the train starts, it pulls the first coupling taut, and then it starts to pull the first car. Then the next coupling gets pulled taut, pulling the next car, and so on. This way, it doesn’t have to overcome the static friction of all the traincars at once. Once the car is moving, it takes far less force to keep it moving or accelerate it.
The train actually can’t start if the cars are already taut. If this happens, the brakes at the back of the train are applied, and the train has to back up slightly. Then, once the train is compressed, it can start as normal.
These two states are called buff and draft. When they are held taut, it’s draft. When they are loose, it’s buff.
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