When I watch documentaries or old movies I always wonder how a single locomotive can drive a train that is often kilometers long. Is there some black magic going on ?
In: Engineering
Momentum! Train carts are very heavy, so a little bit of movement makes A LOT of momentum.
Between each train cart is a connector called a ‘coupling ‘. The important thing is that the coupling isn’t a rigid connection between each side, but instead has a bit of room to move.
So when the locomotive first takes off, it’s just moving the engine. It’ll move a few centimetres and then go ker-CHUNK and engage the first coupling, so the momentum of the engine gets split between the first two carts, and so they have a few centimeters to get some speed.
So now there are two carts moving. And they move a little and go ker-CHUNK. The momentum of the two moving carts is much greater than the next cart, so their momentum is split between the three carts and are able to pull it even easier than the previous one, and then again and again and again.
So the locomotive engine really only has to start pulling one cart at a time to start picking up speed.
In addition to the amount of torque and power that train engines produce, there’s also very little friction between the wheels and the rails. This significantly reduces the amount of energy needed to move the train compared to other forms of transport. [This](https://youtu.be/Au3U72CX74I) video from Engineering Explained goes into detail about why that it is and how much of a difference it makes.
gas and coal locomotives are really powerful because they consume tons of fuel. They burn the fuel, and use the thermal energy to make steam, steam roughly takes 1000 more space than water, so each liter of water becomes 1 cubic meter of vapor. The volume expansion is used to push a piston that will make the whole thing move.
Since locomotives burns a lot of fuel, they can make a lot of vapor, pushing a lot of pistons really strong.
In addition to some of what has been described here so far, one of the key features of modern locomotives is that the powerful diesel engines are often diesel-electric or diesel-hydraulic. That means the diesel engine isn’t turning a crankshaft that’s coupled to the wheels via shafts or gears. They use the diesel to generate electricity and have electric traction motors that turn the wheels, or use hydraulics (much like how an excavator or tank operates…combustion engine driving a hydraulic motor).
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