Scientists overturn a 200-year-old theory: ice is slippery due to molecular dipoles disrupting its crystal structure, not pressure or friction, creating a thin liquid layer even in extreme cold.
For centuries, we’ve been told that ice is slippery because pressure and friction melt a thin layer of water beneath our feet. School textbooks have repeated the story for generations: step onto ice, apply weight, friction or pressure, and a microscopic film of water forms—making slips almost inevitable. But new research from Saarland University has turned this long-standing explanation on its head. The study is published in the journal Physical Review Letters.
According to Professor Martin Müser and his team, the slipperiness of ice isn’t about pressure or friction at all. Instead, it comes down to the tiny electrical interactions between molecules, called dipoles. Water molecules in ice have regions of partial positive and negative charge, giving them a polarity. When ice comes into contact with another surface, like a shoe or ski, the dipoles in the ice interact with the dipoles in the surface. These interactions disrupt the orderly crystal structure of the ice, creating a thin liquid-like layer—even at temperatures far below freezing.
“This isn’t just a minor detail—it overturns nearly 200 years of accepted science,” Müser explains. The original idea, proposed by James Thompson in the 19th century, suggested that friction or pressure caused ice to melt locally. But computer simulations by the Saarland team show that it’s the orientation and interaction of molecular dipoles that truly matter. The forces between the dipoles frustrate the ice’s crystal lattice, essentially turning the top layer into a slippery, disordered state.
The discovery has implications far beyond the winter sidewalk. For instance, it was long thought that skiing in extreme cold—below -40°C—would be impossible because the ice wouldn’t form a lubricating layer. Müser’s team shows that dipole interactions still generate a liquid film even near absolute zero, though it’s far thicker and more viscous than ordinary water. “It’s liquid, but skiing on it would be nearly impossible,” Müser says with a smile.
This research not only rewrites a fundamental concept in physics but also opens doors to new studies on ice, friction, and surface interactions. So, the next time you slip on an icy patch, remember: it’s not your weight or the friction of your shoe—it’s the invisible dance of molecules underfoot.