Brushing
Calibrating the CurlSmart instrumented brush
Frequently, the athletes that I work with on brushing – over 550 since the 2014-2015 season – complain about the CurlSmart instrumented brush for two reasons: it’s, well, heavy. Including the 9V lithium battery, the CurlSmart brush head weighs 534 g, somewhere between 2x and 3x the typical weight of a commercial brush head due to its steel plate construction. The black Cordura nylon fabric on the brush head, which we use for its durability, doesn’t have nearly the same “feel” as a World Curling-approved brush head. Cordura nylon is used on the CurlSmart brush because replacing the fabric on the brush head is a fairly involved procedure that requires disassembling the head, stapling in the new fabric, and reassembling. Moreover, replacing the fabric usually merits a subsequent calibration test of the brush to ensure that the procedure did not impact the brush’s accuracy. Nevertheless, we chose to replace the black Cordura nylon with SportLite+ fabric from Balance Plus in
The physics of curling – with Sean Maw, University of Saskatchewan
This past week, my friend and research colleague Sean Maw, who is the Jerry G. Huff Chair in Innovative Teaching and an Associate Professor in the Ron and Jane Graham School of Professional Development, Division of Biomedical Engineering at the University of Saskatchewan, was interviewed by Matt Olson for the University of Saskatchewan’s Signature Series podcasts. In the interview, Sean outlines a number of research problems with respect to the physics of curling and our short-term research goals for the near future. There remains a considerable amount of work before we come to a more complete understanding of the physics of curling, including the impact of brushing. You can listen to the complete interview by clicking on the introduction at left, or you can listen to the podcast on Apple podcasts (and others) by searching for the University of Saskatchewan Signature Series podcasts. Â
Why bunny-hop brushing may not be the advantage you think it is
Increasingly, this season I’m witnessing the adoption by Canadian Junior and U18 teams of a brushing tactic used by some teams – mostly, but not exclusively, women’s teams – on the Grand Slam circuit. I’ve nicknamed that tactic “bunny-hop” brushing as it involves the near brusher jumping during the “push” portion of each stroke from a snowplough position. Most often I see the bunny-hop used on guards and draw-weight shots, where the tactic is employed between the far hog line and where the stone comes to rest. Typically, the bunny-hop is used when the stone requires additional carry, though sometimes the tactic is also used when trying to both extend the carry of a stone and, at the same time, accentuate curl by brushing in the direction of the stone’s rotation. https://youtu.be/o2woYB05zdU?&t=1843 Carole Howald of Team Tirinzoni uses the “bunny-hop” brushing tactic vs Team Homan in the final of the 2025 AMJ Campbell Players’ Championship. Rationale The idea behind the
A brush is not a rock magnet
A brushing tactic I continue to see being used by younger teams is to brush the ice adjacent to the stone when trying to ‘carve’ or accentuate curl. I’m not sure where this tactic began, but there is no point in brushing ice that the running band of the stone will not pass over as the stone continues its trajectory. Brushing to increase curl requires brushing ‘high-side’ (in the direction of the stone’s rotation). Precisely where the stroke begins and ends for optimal effect depends on a number of factors, the most important being the velocity of the stone and the force profile of the athlete(s) doing the brushing. But there are several other variables that may play a role, including the roughness of the stone’s running bands, the ice conditions, and environmental factors (temperature, humidity, dew point) to name just a few. These variables are not completely understood, and we know from testing – at different clubs with various
Foamgate, existing, and forthcoming research
At this point, many competitive curlers in Canada should be familiar with the recent announcement from World Curling about the withdrawal of specific foams in a small selection of brushes from World Curling’s approved equipment list for competitive play for the upcoming 2025 – 2026 season. World Curling came to their decision based on the outcome of brush testing in Morris, Manitoba during the Victoria Day weekend, along with feedback from the researchers on World Curling’s equipment advisory group, of which I am a member. To a significant extent, World Curling really didn’t have a choice but to try to address the concerns first brought to their attention with the players’ manifesto that was put together just prior to the Grand Slam event in Guelph this past January at the WFG Masters. The players who signed onto the manifesto were concerned that the brushes approved for competitive play this past season were too good: either they permitted additional carry above reasonable
We are getting closer to understanding the physics of curling
Last year, 2024, marked the 100th anniversary of the first scientific article that I’m aware of that investigated the physics behind the sport of curling; a 1924 paper [5] by E. L. Harrington and his colleagues in the College of Engineering of the University of Saskatchewan in Saskatoon. In the 100 years since Harrington’s work, scientists and engineers have investigated various aspects of the sport, but our understanding of one of the sport’s singular fundamentals – why does a curling stone “curl” – remains incomplete, if not vague. There have been dozens of articles, authored by scientists and engineers from Canada, Sweden, Finland, China, Japan, and Korea, that have investigated the question of why stones curl the way they do, frequently contradicting each other’s mathematical models and none of them fully explaining all of a stone’s observed behaviours. At the same time, there are other aspects of the sport, particularly surrounding brushing, that have not been studied extensively and remain