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Feb25-12, 12:11 PM
Sci Advisor
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P: 26,148
actually, there are units which are confusing in this way

eg the resistivity, ρ, of a material

(also conductivity, permittivity, permeability)

(by "a material", i mean eg copper, as opposed to a particular copper wire)

ρ is measured in ohm-metres (Ω-m),

but it's really Ω-m2 per m

because resistance R = ρl/A (l = length of the wire, A = cross-section area)

calling it Ω-m is confusing!
however, the combining of length and area (in resistivity) is different to the second-squared in acceleration

in resistivity, we can change l and A separately (the are two different measurements), so arguably they deserve to be mentioned separately in the units

but in acceleration, the second-squared only involves one measurement, so there's no confusion