Curling: inspirational to scientists

We all have interests which seem odd to those who don’t share them. Maybe it’s stamp collecting. Maybe it’s science fiction. Maybe it’s watching NASCAR races.

Whatever our interest, when we are called upon to defend it, we’re usually reluctant to give the real reason, which is generally no more complicated than, “Because I enjoy it.” Instead, we search for some reason more practical, more socially responsible.

Take curling, for instance.

Those from places where the roaring sport is less well-established (hello, friends in Texas!) sometimes find it hard to comprehend the sport’s appeal. As a result, those who curl or who watch those who curl are sometimes called upon to defend their interest. Alas, utilitarian reasons for being interested in curling have been hard to come by—until now.

Materials scientist Jane Blackford and her research team from Edinburgh University were called upon to help out Great Britain’s curling team in 2000. Blackford’s team helped developed a “sweep ergometer,” which measured how the broom was moving and how hard it was pushing against the ice. By monitoring their sweeping, and its effect on the rocks, team members were able to improve their technique.

Inspired by her work with curling, Blackford decided to look deeper into the question of the slipperiness of ice—still something of physics mystery.

For a century or so the stock explanation (one I recounted myself in my first column on ice circa 1994) was that ice is slippery because the pressure of a foot or skate blade on it compresses it. Because ice is less dense than water, increasing its density lowers its melting point.

Unfortunately, it turns out that the pressure exerted by a person standing on the ice, even on a thin skate blade, isn’t enough to lower the melting point of ice by any significant amount.

A second explanation, probably the most widely accepted right now, is that ice is slippery because friction between objects and ice melts the ice, creating a thin lubricating film of water. However, another theory holds that ice is slippery all the time, whether anything is rubbing against it or not, because the water molecules at its surface vibrate more than those trapped further down. As a result, ice is covered with a thin quasi-fluid layer even when the temperature is far below freezing.

Some scientists hedge their bets, and say both the quasi-fluid layer and friction play a role.

Blackford’s team has focused on friction—friction, after all, plays a large role in curling, with both the sliding rock and the brooms melting the ice and making it slipperier. They’ve built a new device to measure the friction between ice and various substances.

Called the Tribometer, it looks a bit like a record player. The needle-shaped test sample—rubber, say, or perhaps steel–is placed in a mount which is held in place by deflection arms. The load on it can be adjusted by adding weights. During experiments, strain gauges are attached to the deflection arms to measure the amount of movement caused by friction.

The ice sample is mounted in a circular tray connected to a motor. The needle-shaped sample is brought into contact with the ice, the motor is turned on, and the sample rubs against the ice. After the experiment is concluded, the test substance and the ice are examined. A Low Temperature Scanning Electron Microsocpe allows the team to view what has happened to the ice surface at a variety of scales, from several millimeters to just a few nanometers.

The team has already discovered that at “high” ice temperatures, around -5 C., friction creates ripples in the ice because some ice melts and then refreezes. At lower ice temperatures, around -23, friction instead causes the ice surface to fracture.

Knowledge of how ice behaves under friction may benefit curlers, skaters, and other winter athletes, but it’s also important for understanding how other materials move on ice, too: tires, for instance (which is why Jaguar Cars has funded Blackford’s research).

According to Bob Williams, a research engineer with Jaguar, the research could lead to better anti-lock braking systems, improved traction-control systems, and grippier winter tires.

“All this stems from curling,” says Blackford.

And there you go. You love curling because it’s making winter driving safer for all of us.

What better reason could there be?

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