Scientists discover magnus effect at microscopic level, opening new possibilities for microscopic control

The Magnus effect is a phenomenon we often encounter in sports like football, cricket, or baseball, where a spinning ball deviates from its expected path, surprising opponents. This principle also has practical applications in engineering, such as propelling certain ships and aircraft with “Flettner rotors.”

Recently, physicists have demonstrated that the Magnus effect operates on a microscopic scale, potentially offering significant benefits under specific conditions. Researchers at the University of Konstanz conducted experiments, while a team at the University of Göttingen explained the science behind it.

These discoveries could pave the way for innovative mechanisms to move and precisely manipulate tiny particles. Imagine mini-robots navigating the bloodstream to target specific areas in the body. These findings were published in Nature Physics.

Normally, the Magnus effect occurs when a rotating object moves through air or liquid, causing differences in velocity around the object, which deflects it from its straight path. As objects shrink in size, this effect diminishes and should virtually disappear for spheres just a few thousandths of a millimeter in diameter.

The track (green line) of a rotating particle moving from left to right in water (top) and a viscoelastic fluid (bottom). In water, the particle moves constantly to the right regardless of its direction of rotation. In a viscoelastic fluid, the Magnus force leads to deviation from a straight path. Credit: Niklas Windbacher, Bechinger Research Group

However, the University of Konstanz experiments revealed an unexpectedly strong Magnus effect in miniature magnetic glass spheres rotating in a viscoelastic fluid (like blood or polymer solutions). Unlike water, viscoelastic fluids exhibit both fluid and elastic properties and respond to changes with a delay, much like dough slowly returning to its original shape.

Dr. Debankur Das and Professor Matthias Krüger from the University of Göttingen’s Institute for Theoretical Physics developed a model explaining this microscale Magnus effect. The delay in the viscoelastic fluid’s response to the rotating sphere causes distortion, pushing the sphere sideways, coupling rotation and translation. Interestingly, even when the rotation suddenly stops, the Magnus effect lingers for a few seconds in miniature spheres within viscoelastic fluids, unlike traditional sports balls in the air.

Krüger stated, “Understanding this after-effect was crucial. Our model predicted it, and when we observed it in the experimental data, we unraveled the mystery of the Magnus effect on a microscopic scale.”

Source: University of Göttingen

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