Its not a moment, but its still a sprung system. (cantilever is the spring)
In the case of air arms, the whole sled generally moves in the horizontal, while they have piddly short arms tubes which moves in the vertical. Certainly the Terminator is like that. Others are different, though.
Dynavector is another that would be like a linear,
Some waffle on there about it.
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Yep.
Yeah but basically different maths - just a weight on a spring, so it’s actual mass (horizontal) rather than effective mass (vertical), yeah?
The maths is the same. The numbers are different.
I suppose it’s the same maths once you introduce the concept of effective mass, yeah
Sometimes effective mass == mass, sometimes it doesn’t. Where it doesn’t, you need to work out the effective mass, which requires a bit of additional maths. 
P.S. both Both H&V it’s effective mass that’s important.
Massematics FTW
I have always considered effective mass a wishy washy term anyway, not sure its used in the same way outside of tone arms. Always seen it a little pointless trying to work it out, much easier to stick on a test record and see where the arm has a fit.
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Yep. Essentially impossible to work out, easiest way is to measure compliance and resonance, then back calculate.
How much would effective mass change for the cm or so that the cartridge can slide back and forth in the headshell?
Somewhere between a cunt hair and a pube.
It’s worth trying to understand why its preferable to have a heavier counterweight closer to the pivot.
CNC yourself a tonearm, then you’ll have a perfect model where you could actually work it out. How’s your integration?
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And also why it’s not always in practice. (While I’d agree that theory says it’s preferable, I’ve heard it sound worse, go figure).
Assuming the arm was equally stiff/dead then it wouldn’t matter.
Since they wouldn’t be, which one sounds best is probably down to preference, people love wibbly wobbly arms with lots of wobbly bits (triplanar)
Surely it depends as much on the cartridge. Reducing the effective mass of the arm (by putting a larger weight nearer the pivot) will raise the resonant frequency of the sprung part to a point where it might become excited by LF on the record.
Wait, what? Surely the effective mass will be the same, the benefit of heavier counterweights comes in lower resonances?
Too many variables and depends how close you can get it to the pivot, but you could lower the effective mass by having a short counter weight mount and heavy weight, vs a long one and a lighter one.