How do trains pull so much weight? I’ve seem them with hundreds of freight and gas tanker cars.
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Trains are able to pull so much weight because they can balance the force applied to rotate the axels with a near equal force on the couplings.
It’s misdirection in my view to talk about torque or HP, the ability to pull load here is about traction force.
The locomotive’s engine develops a traction force, many factors go in to traction force being correct including wheel size, and the needing to safely stop.
As this is eli5 there is no math, if you wanted to do some you would need like – The wheel-rail adhesion coefficient, and to know traction force is expressed in Newtons (N) and the weight in KN.
The adhesion-limited force defines a safe upper limit of the traction force. If the traction force is greater than this limit the wheels will slip.
At very low speeds the traction force is very high – and the locomotive can pull or stop a bigger weight.
But also at low speed, especially just when movement starts, the loco needs to overcome the adhesion between the wheels and the rails, otherwise the wheels will slip, rotating in place and damaging the rails.
But why do we need such big engines –
For a railway to operate efficiently and safely, its locomotives should be powerful enough to accelerate their trains rapidly to the maximum allowed line speed, and the braking systems must be able to bring a train reliably to a standstill at a station or signal, even on an adverse gradient.
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