It’s the season of the 2026 Olympic Winter Games in Italy, and it has already been circled for its strict stand on PFAs or ‘forever chemicals’ used in ski wax. The first Winter Olympics to enforce this novel principle, three athletes were disqualified on this ground. The best part of this Winter Olympics, as in all others, doesn’t lie in the environmental aspects as much as in the human feats that stretch the laws of physics to the farthest extremes. Be it a bobsledder taking on a force of 5Gs, or a figure skater spinning four times in a single jump, muscle memory in sync with physics never gets old.
While most of these sports have magnitudes that seem unreal, curling has defied the usual principle. Physicists still don’t entirely understand why the heavy granite curling stones travel in the direction that opposes expectations. If you spin a round object, such as a bowl, clockwise on the floor while pushing it forward, it always curls to the left— in the opposite direction of what we see in the curling event.
Curling is a lot like shuffleboard, played by two teams of four. While one of the players slides the roughened granite stone with a spin, other team members “sweep”—brushing the ice to help the stone travel. The ice surface on which the stone slides is “pebbled” with frozen water droplets, which impart friction that eventually slows the stone to a halt. The closer a stone is to the target, the higher the points scored.
Physicists have spent over a century trying to figure out what actually causes the curling stone to behave differently. Scientists have since split to support different hypotheses explaining the physics behind it. One idea suggests that the running band – the rough circle on the underside in contact with the ice– creates scratches in the pebbled surface. When a stone spins clockwise, the back end of the rotating stone runs into scratches left by the front, and it goes toward the right.
In 2016, physicists described the ‘pivot-slide’ model, which suggests that the stone’s movement arc across the ice is not one, but a collection of multiple smaller movements. In a stone rotating clockwise, a point on the right side will always anchor on the ice, pivot slightly, then unlatch and glide forward. Many such small pivots in a row create a curling effect. This “happens more easily further down the ice because the speed of the rock is reduced”, says Mark Shegelski, a physicist at the University of Northern British Columbia in Canada who is a co-author on the 2016 paper.
‘Pivot’ing on the earlier hypothesis, in 2022, Jiro Murata at Rikkyo University in Tokyo, drew a similarity to how the stone’s friction is compatible with the concept of a pivot point. Using image analysis, he tracked each stone’s movement across the ice down to one one-hundredth of a millimeter. When spun clockwise, the right side of the stone produces more friction, and the friction points act as a pivot, swinging the stone around.
Later, Clifford Jenkins, who lives in Toronto, Canada, and is a curler, partnered up with his son, an aerospace engineer, to see if asperities or microscopic protrusions on the bottom of the stone, created by sanding the stone, can influence the curl. Jenkins started this project to demonstrate the best sweeping method in curling, only to find that the underlying physics needed more explanation.
In their experiment, Jenkins and his partners had a proficient curler throw different types of stones; some with short protrusions, others with long ones. Longer protrusions created larger curls, and both his and Murata’s findings back up the pivot-slide model. A curling stone experiences different phases of friction during its course down the ice. Different models, therefore, apply to particular phases, which makes the answer to the curling mystery a multitude of theories fused together.
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