Parallel-disc viscometer
= Parallel-disc viscometer
{title2=$\tau=\pi\eta\omega a^4/(2d)$}
In the thin-gap, laminar approximation, a rotating disc of radius $a$ separated by $d$ from a stationary disc shears a <Newtonian fluid>. The resisting <torque> is $\pi\eta\omega a^4/(2d)$, neglecting edge effects and secondary flows. This gives a way of inferring <dynamic viscosity> from a measured <torque>.