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
There’s a pretty simple equation that’s helpful here, F = ma, or in words: force = mass(for our purpose here it’s pretty much just how heavy our object is) * acceleration. As someone else mentioned, the friction of the wheels is pretty much negligible, so we can ignore it really. Trains are pretty strong so our pulling force is pretty strong, but we’ve got a TON (or more accurately, tons, haha) of mass. This means that the acceleration has to be really low. Acceleration is basically how fast an object is speeding up, so a low acceleration means that train is barely speeding up, and that’s exactly what happens, trains take ages to get up to full speed!
Inertia is an interesting topic, but it doesn’t really effect our F = ma equation up above. Basically inertia is directly correlated to mass, so an intuitive way to understand this might be to look at something on a slightly smaller scale, like a human pushing a car that is in neutral. Assuming we’re on relatively flat ground, a human can probably push something with roughly 100lbs of force or so. Meanwhile, a car can weight a couple thousand pounds, roughly 10-20x more, but a human can still push it get it moving. It’s slightly oversimplified, but it might help you understand whats going on in the train situation a little more intuitively.
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