John Carlos Baez on Nostr: QUINCKE ROTATORS If you put a small uncharged sphere of stuff in a liquid and turn on ...

QUINCKE ROTATORS

If you put a small uncharged sphere of stuff in a liquid and turn on uniform, unchanging electric field, the sphere can start turning around! How does it work?

I read that

"The spontaneous rotary motion of a solid, dielectric particle in a low conductivity fluid under a direct current (DC) field was observed by Quincke in 1896 and is now commonly referred to as ‘Quincke rotation'."

and

"Quincke rotation is best explained using the much celebrated Melcher-Taylor leaky dielectric model that proposes the formation of a surface charge on the particle-liquid interface. Rotation occurs due to the symmetry breaking of the charge distribution that gives rise to a net torque leading to steady rotation of the particle."

But I'm still mystified by how it can happen - why should an asymmetrical charge distribution on a particle in a constant electric field make it want to keep turning around, instead of just turning around to line up with the field and then coming to rest?

Here's a movie of the effect: