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The Science of Curling

Feb 19, 2018

This post was originally published by Battelle , which manages STEMx, and it’s too good not to share. Have you integrated curling (or any other Olympic sport) into your classroom? Please tell us about it in the comments below.

At Battelle, we take science seriously. And, our researchers may take their hobbies just as seriously as their science. Rick Olson, a mechanical engineer who has led structural analysis projects at Battelle for 41 years, is also an active member of the Columbus Curling Club. He plays the ice sport several days a week and has participated is numerous tournaments, known as bonspiels, over the last decade.

With the  Winter Olympics  underway in Pyeongchang, South Korea, we asked Rick to share the science behind the sport.

What makes curling ice special?

Curling ice is not hockey ice. It’s very different. Although it’s hard to see, hockey ice isn’t very flat. The curling surface must be remarkably level. If it’s not level, the stone will “fall” sideways as it moves down the ice. A slope as little as 0.005 inches in the 15-foot width of the curling ice can cause the stone to move an extra 30 inches laterally as it travels down the 150-foot sheet.

Making perfectly level ice isn’t easy. When water is added to create new ice, it naturally wants to curve up at the edges to form a meniscus. It also doesn’t freeze uniformly when it’s created due to hotter and colder spots in the cooling coils in the floor. To compensate for the inevitable imperfections, the high spots are removed by scraping and the low spots are filled in with droplets of water broadcast onto the new ice. In addition to the droplets applied to the ice when it is made, it is “pebbled” before each game with small droplets of water to make asperities, creating a texture similar to an orange peel.

Why do the curling stones slide so effortlessly down the ice?

When you watch curling, it looks like the stone will go forever, even though it is not moving very fast. On good curling ice, it takes 25 to 28 seconds from the time the curler releases it until it comes to rest at the other end.

This is because the stones are not flat on the bottom. They are concave with a running band about five inches in diameter and a quarter of an inch wide. Combined with the bumpy texture of the ice, very little of the 44-pound stone is in contact with the ice surface. This creates high pressure that keeps the surface under the stone right on the edge between solid ice and liquid water, which reduces friction. Think about ice skating.

The stones are made primarily from granite quarried in Scotland. The material repels water, has high fracture toughness, and behaves almost perfectly elastically in collisions, meaning stones continue gliding after they hit each other. Each curling stone costs around $1,000 (or as much as $2,000 for the special high-level competition ones) and can have a useful life of a century.

What makes a curling stone curl?

There’s been debate for many years between scientists trying to describe the physics of the underlying mechanism that makes the arching path of a curling stone. It’s incredibly difficult to describe the forces acting on the stone because more spin doesn’t translate to more curl. Typically, three to five revolutions of the stone on good ice causes it to move 3 to 4 feet side-to-side as it goes down the length of the sheet. If you spin a stone hard, it won’t curl at all.

The scratch guiding model is the best explanation. The bottom of the stone is textured. As the nose of the stone goes over the small bumps in the ice, it creates scratches. When the back of the stone goes over those scratches, microscopic forces move it in the direction of the scratches.

Why are those guys sweeping in front of the stones?

When you sweep in front of the stone, you are polishing the surface of the ice, reducing the height of bumps and scratches. While sweeping doesn’t actually cause the surface to melt, it does raise the temperature closer to the boundary between ice and water, which lowers the coefficient of friction and fracture strength of the ice. The result is a stone that doesn’t slow down as much and appears to go straighter. Good sweepers can drag a stone 10 feet farther down the ice.

Rick Olson giving a presentation on the science of curling at Battelle
By Rob Evans 01 Nov, 2023
by Heather Sherman, Director of STEMx The 2023 STEM Innovation Forum: Activating Collaborations to Advance an Inclusive STEM Workforce was a success! Through our collaboration with STEMconnector and Million Women Mentors, we convened 160 leaders from industry, government, non-profit organizations, and education institutions from all over the United States to discuss strategies and best practices to support the STEM workforce. We were honored to host a variety of dynamic speakers including: Jared Polis, Governor of Colorado Brynt Parmeter, Chief Talent Management Officer, U.S. Department of Defense Dr. Athina Kanioura, Executive Vice President, Chief Strategy and Transformation Officer, PepsiCo and Dr. Lisa Hinkelman, Founder and CEO of Ruling Our eXperiences (RoX). We extend our gratitude to our panelists, Learning Session speakers, and participants who joined us in Denver. Broadening participation We set out share information on trends in STEM education and workforce development, with an emphasis on broadening participation in STEM careers. Resources from sessions highlighting strategies for broadening participation are linked below: DoD STEM: Developing a STEM Workforce to Support the National Security Mission Priming the Pump for High Demand STEM Careers STEM Workforce Readiness for Teen Girls: “If She Can See It, She Can Be It” Driving change Another goal of the forum was to feature high impact strategies, programs and solutions that are driving change, and STEMx members from LASTEM , the PAST Foundation and MBRT showed how they are engaging youth and building career awareness through their workforce programs. Emerging technologies We looked towards the future to better understand how emerging technologies will change the world and the ways we must prepare STEM talent for jobs in logistics, artificial intelligence, research safety , bioenergy , and renewable technologies. Chevron‘s sponsored panel, “Cultivating the Talent to Drive the Innovation and Technologies for Ever-Cleaner Energy” was a rich discussion featuring experts from Chevron, Project Lead the Way and the National Renewable Energy Laboratory. Dr. Jamie Vernon, Executive Director, and CEO, Sigma Xi Society was a fantastic moderator for this discussion. Next steps We have linked event resources including videos, slide decks and collateral on the event landing page . The event photo gallery is located there as well. If you attended, please complete our 30 second event survey . Five lucky winners will be selected at random to receive a Forum water bottle! More importantly, your feedback matters to us. If you did not attend, mark your calendar for next fall - we’re looking to make next year even bigger! If you are interested in hosting in your state, or have thoughts about compelling content that we should include, please reach out to Heather Sherman .
By Rob Evans 03 Oct, 2023
Join us for The STEM Innovation Forum: Activating Collaborations to Advance an Inclusive STEM Workforce
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