How are trains able to start with so much cargo?

Question

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

Answer 1

Moving large trains, sometimes with more than a hundred freight cars, needs enormous amounts of torque (torque is the force applied by the engines on the wheel axles to make them turn). Road vehicles like cars and trucks achieve this by using a series of gears. Automatic cars typically have 6 to 12 sets of gear combinations to achieve the desired amount of torque and efficiency. If you drive a manual transmission car you would notice that you are starting in neutral and then shift to first gear and then gradually move up the ratios as the car advances in rpms and speed. The first gear provides the most amount of torque, hence it is used to get the car moving forward. Large semi rigs carry many tonnes of load so they need huge amounts of torque. They often have 18 to 20 gear ratios. A freight train carries thousands of tonnes of freight. It will be impossible or impractical to use hundreds of mechanical gears to achieve the gigantic amounts of torque needed to get this train going. This is where electric motors come to the picture. Electric motors can generate lots of torque very easily compared to internal combustion engines. So strap some powerful electric motors to the axles of locomotives, we solve the problem of torque, along with some other advantages. All you need is electric current to run the motors. This is where the diesel engine comes in. The diesel engine, connected to an electric generator burns diesel fuel and produces the eclectic current to turn the axle motors. That is why the diesel powered locomotives are called diesel-electric locomotives. Put three or four of these powerful locomotives together, that’s all the power you need to get a 80 car freight train moving.