Curling researchers dig deep into sweep science

As scandal roiled the curling world in 2015 – with the discovery that athletes using ‘Frankenbrooms’ were converting missed shots into miracles – curlers began to speculate about the science of how a rock’s direction could be manipulated so dramatically.

Now a pair of Western engineers has come up with at least a partial answer, by measuring the topography of an ice sheet after it’s been scoured by different broom heads.

They discovered some head materials, banned since Broomgate, can cause deep ice scratches that could alter a rock’s curl and direction.

Scratches made by an approved broom head, meanwhile, measured one-quarter the depth of some of the now-banned head fabrics.

And while researchers haven’t solved all the questions about why rocks curl – or don’t – they’ve already drawn some international attention for their research, recently published in MDPI Proceedings.

“This week, a top-five athlete contacted me to ask more about the paper,” said co-author Megan Balsdon, who is working towards her PhD in mechanical and materials engineering and is an elite provincial-level curler. “I think we’ve sparked some conversation.”

Co-author Jeffrey Wood, professor of mechanical and materials engineering, said some researchers have dissected sweeping techniques and others have studied rock science – but this is the first time anyone has examined and measured, microscopically, a swept ice surface.

To understand how significant this is, you first have to know how a shot behaves under ordinary conditions:

As a rock leaves the curler’s hand, she or he gives it a rotation, which ensures the rock curls slightly instead of taking a straight lane down the pebbled ice sheet.

The curler’s teammates then vigorously sweep in front of the rock, reducing friction between the ice and the rock’s running surface – thereby straightening the curl and increasing the rock’s travelling distance.

All that sweeping is intended to maximize the skill of the curler.

Only, in 2015, things changed.

Some teams started competing using a new broom-head fabric, more abrasive than previously used, that could be used for ‘directional’ sweeping. With the right broom and the right technique, a skilled sweeper could now transform a poor shot into a great one.

six curling broom heads

Of these six curling broom heads, only the yellow one on the far left is now approved for international competition.

A game previously based on curlers’ strategy and precision instead became a battle of the sweepers.

“It really took the skill of the game out of it,” Wood said.

Many in the curling community cried foul. They held an international sweeping summit and, based on observations of how rocks behaved behind different broom materials, the World Curling Federation ultimately approved and standardized just one type of fabric.

“But we still didn’t really know what was happening at the level of the ice,” noted Balsdon.

Their study compared a legal broom to six others that are now deemed illegal. Conditions (ice and air temperature, pebbling, the same sweeper) were identical; the only variable was the type of broom used.

After each sweep, Balsdon placed over that patch of ice a type of putty (usually used to help make dental implants) that quickly set and captured an impression of the ice topography.

Under a microscope, four of the now-illegal broom heads had caused significantly deeper scratches than those made by the approved head.

“For the most part, this (legal) material is doing what we as curlers want it to do,” Balsdon said. “The legal broom material is still maintaining the integrity of the game.”

Interestingly, two of the banned broom heads also compared well on the scratch test with the approved one.

Added Wood, “If anything, the data that came out of this might allow other fabrics to join the family of legal materials because they don’t affect the integrity of the game.”

Balsdon, meanwhile, is focusing on broader research questions about why curling rocks, unlike other objects, move into the direction of rotation instead of against it. She also has her sights set on competing in the Scotties Tournament of Hearts and helping her team qualify for Olympic pre-trials.

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