  In novel ultra-pure materials electrons can form a viscous fluid, which is
fundamentally different by its dynamics from the electron gas in ordinary
conductors with significant density of defects. The shape of the non-stationary
flow of such electron fluid is similar to the alternating flow of blood in
large-radius arteries [J. R. Womersley, J. Physiol. 127, 552 (1955)]. The
rotational viscosity effect is responsible for interconnection between the
dynamics of electron spins and flow inhomogeneities. In particular, it induces
the spin polarization of electrons in a curled flow via an internal spin-orbit
torque acting on electron spins. Here we show that this effect in an electron
fluid placed in a magnetic field leads to a correction to the ac sample
impedance, which has a resonance at the Larmor frequency of electrons. In this
way, via the electrically detected spin resonance the Womersley flow of an
electron fluid can be visualized and the rotational viscosity can be measured.
