= Tidal water loading of a spring balance
{title2=$\Delta x=x_0\,2\pi G\rho h/g$}
A <mass> above a sufficiently wide estuary experiences additional downward <gravity> when extra water is present. Approximating the tide as a plane slab of <density> $\rho$ and added thickness $h$ gives $\Delta g=2\pi G\rho h$. A linear <spring> with initial extension $x_0=mg/k$ changes by $\Delta x=(m/k)\Delta g=x_0\Delta g/g$. This isolates direct water attraction; it omits finite shoreline geometry, buoyancy, structural motion and terrestrial tides.
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