In this relationship, dℓ is the incremental change in the length of the box and ρ is the one-dimensional “pressure” contribution from each molecule. ρ is, of course, just the forc...In this relationship, dℓ is the incremental change in the length of the box and ρ is the one-dimensional “pressure” contribution from each molecule. ρ is, of course, just the force required to push the end of the box outward by a distance dℓ. ρdℓ is the one-dimensional analog of PdV.) For the one-dimensional system, it follows that ρ=−(∂A∂ℓ)T
