Quincka

Quincka, a silver-haired field-dancer, holds a spinning glowing disc between two plates.

The Physics

In 1896 Georg Quincke saw that an insulating sphere in an oil, placed in a strong steady electric field, can start spinning on its own. Charges pile up on its surface; above a threshold field the arrangement is unstable and a small tilt grows into steady rotation.

E > E_c → rotation

• E: applied DC electric field (V/m)
• E_c: threshold field for spontaneous rotation (V/m)

Quincke rollers are now used to build self-propelled colloids that flock like birds.

Honest caveat: The direction of spin is chosen at random; the effect needs the particle to relax charge more slowly than the liquid.

On the sticker

Quincka holds a glowing cyan spinning disc between two upright plates. Printed text: QUINCKA. Pixel-art kiss-cut vinyl sticker, white, in 2″, 3″, 4″ and 6″ sizes.