Curling stone curl direction

Still disputed in the literature as of 2026.

Curlers have known for centuries that a stone rotating clockwise drifts to the right as it slides, opposite to what basic friction intuition suggests, but no rigorous mechanism was agreed until physicists began quantitative study in the late 20th century. Competing camps have proposed a front-back asymmetric friction/thin liquid film model (Shegelski, Jensen and collaborators) versus a model where the granite's micro-asperities scratch directional grooves into the pebbled ice surface that steer the stone (Nyberg and colleagues at Uppsala). Both camps have published data supporting their own model and criticizing the other's, and as of the mid-2020s no single mechanism has been broadly accepted by the tribology and sports-physics communities. It remains an actively studied, genuinely disputed problem, unusual for a sport with such simple-looking physics.

A game played on ice for 500 years still has no agreed physical explanation for its single most famous move, even though thousands of physicists have watched it on television.

Explanations that circulated

• Naive point-contact friction models predict a curling stone should either curl opposite to its spin direction or travel straight; both are contradicted by observation, showing the real contact-patch physics is more subtle
• A single 'pivot-slide' explanation is often stated in popular science articles as settled, but it has not been reconciled with the competing ice-scratch-guiding model backed by other experimental groups

References

• The asymmetrical friction mechanism that puts the curl in the curling stone, P. Nyberg, S. Alfredson, S. Hogmark, S. Jacobson, Wear, 2013
• A surface topography analysis of the curling stone curl mechanism, Harald Nyberg, Christer Alfredson, Sebastian Hogmark, Staffan Jacobson, Scientific Reports, 2018