Researchers from the University of Waterloo have achieved a feat previously thought to be impossible—getting a sphere to roll down a totally vertical surface without applying any external force.

The spontaneous rolling motion, captured by high-speed cameras, was an unexpected observation after months of trial, error, and theoretical calculations by two Waterloo research teams.

“When we first saw it happening, we were frankly in disbelief,” said Dr. Sushanta Mitra, a professor of mechanical and mechatronics engineering and executive director of the Waterloo Institute for Nanotechnology.