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Hi FolksMy first post to your extraordinary site...so impressed...thanks.'Shakamaker' from 'Trainorders.com' in 2001 wrote... "BHP Iron Ore in the north west of Australia ran the worlds heaviest ( and possibly longest) train on Thursday evening. The train was powered by 8 AC 6000hp locos and weighed in at a staggering 82,000 wet metric tonnes + tare weight of vehicles I presume for approximately 95,000 metric tonnes. The trains length was 7.353km (4.55 miles) long." Well, that is where I live and I remember the train well, and saw it! And the info here is correct.I was wondering if anyone can calculate the relativistic effects on the train given a gross mass of 100,000 metric tonnes, and a length of 7.0km (7,0000m), at a speed of 75kmh (that railroad's maximum permitted speed for empty or loaded iron ore trains.)I am interested in the mass and dimension changes as compared to when the train is at rest. I've tried the calculation myself but get really messed up with the number of final decimal places, and I don't know if I end up talking in milligrams, micrograms etc or micrometres etc.The effects are minuscule, which is the point of the exercise. To demonstrate the little relativistic effect upon massive (by human standards) objects at everday speeds...Thanks if you can help,Democritus

I am interested in the mass and dimension changes as compared to when the train is at rest.

Hello lightarrow: Why doesn't the mass of the moving train increase relative to the stationary train? It should, according to SR.stevewillie

I don't follow that bit; if you accelerate an electron to high speeds in a Betatron, you need to take account of an effective increase in its mass.

A simple Cyclotron won't work. Isn't that a relativistic increase in mass? Or, should I say, can't it be explained 'in terms of' a relativistic increase in mass?

What has changed about that since I was at Uni?

Hmm... well it does take more force than expected to keep a particle in a bevatron on course as it is accelerated (beyond the force required to compensate just for it's velocity).

Of course, these masses are measured in Ev and not kg, and I wouldn't swear to how they relate to each other without checking up and reminding myself.

To make my question more concise, if the rest mass of the train is m and the mass of the moving train is m*, then the KE of moving train is m*v^2/2 and the PE is m*c^2? This would mean that the train gains potential energy by virtue of moving. Is this consistent with SR?

Thanks lightarrow. Gamma is the Lorentz factor {1/sqrt(1-(v/c)^2}, is it not?

. If you multiply the Lorentz factor by mc^2, it seems this is equivalent to m*c^2. It appears that this is two ways of expressing the same thing

, but particles in accelerators are driven by external forces (energy is added)while the train is powered by fuel which is part of its mass. I'm not sure the two situations are really comparable.s