Skis used by Olympic Alpine and Nordic skiers are made of fiberglass and polymers, engineered by materials scientists to give skis used in different events the flexibility, stability and torsional rigidity required. NSF-funded scientists Melissa Hines, Director of the Cornell University Center for Materials Research, and Kathy Flores, an Ohio State University materials scientist, explain how skis are made, from the core to the ski base, with help from three members of the U.S Olympic Ski Team: Julie Mancuso, Scott Macartney and Ted Ligety.
The Science of Skis
LESTER HOLT, anchor
In skiing events like the downhill, slalom or ski jump it’s often the skis bound to athletes feet and the materials used to make them that give these athletes an edge over the competition. This year's Olympians along with researchers funded by the National Science Foundation explain how the materials used to make their skis play a vital role in performance on the mountain.
HOLT: They barrel down the mountain, fly through the air, weave through gates, beating the competition by only hundredths of a second -- athletes on skis, long slender runners that glide over the snow.
Skis used to be made of simple wood slats - but today's skis are marvels of chemical and materials engineering.
Dr. MELISSA HINES (Cornell University): Over the past say, hundred years, there's been a real evolution in the properties of skis going from single material wood up to multi-material composites.
HOLT: Today's skis use fiberglass - a composite material made from fibers of glass, arranged and embedded in a glue, or epoxy.
Dr. KATHARINE FLORES (Ohio State University): So in the ski, we would have-- a blanket of fibers that are all pointing say along the ski, and then perpendicular to the ski. And that's what's really giving it that-- that stiffness in that direction. And-- and it's torsional rigidity.
HOLT: "Torsional rigidity" refers to how a material reacts to shearing and twisting forces.
Dr. FLORES: If you wanted to-- to minimize the torsion and increase the torsional stiffness, you really would want to wrap the ski with-- with a fiberglass or some sort of fiber-reinforced material.
HOLT: By arranging fiberglass layers, ski-makers can engineer a downhill ski that is more rigid and remains more stable at high speeds, like the ones used by Olympic Gold Medalist Julia Mancuso to race downhill at speeds of up to 90 miles per hour.
JULIA MANCUSO (U.S. Ski Team – Alpine): The more you go for it and push the limits, the safer it is because you are in control. You’re not waiting for things to come at you.
HOLT: Skis are engineered to dampen vibration, and reinforced with steel inserts to decrease twisting and help the ski stay in contact with the snow.
Dr. FLORES: If we look at the-- the cross-section of the ski, right at the edges we have these steel strips and that's really to help-- help maintain that edge and maintain the cut into the snow. If it starts to twist, now you lose your edge. You lose your grip on the snow, and you wipe out.
HOLT: Some Alpine sports benefit from skis that are less rigid, more flexible. For slalom races, skiers need a ski that can bend just the right amount on the turn, then quickly regain its shape. Ski jumpers, too, need more flexible skis.
While the exact 'recipes' for making skis are usually trade secrets, manufacturers can now make a ski that is remarkably flexible. Watch this bend test.
Dr. FLORES: When we were looking at the-- the ski bending really what we were trying to show is just how much flex you can get out of the ski. I think we were going through a five or six inch travel, so if you're, say, doing-- a ski jump, you want to be able to-- to get-- use the springiness of the ski, to-- to improve your jump.
HOLT: It's not just the core material of the ski that's important - it's the material on the outside of the ski that directly interfaces with the snow. What gives modern skis their smooth outer surface? It's the epoxy used to make the fiberglass - called a polymer.
Dr. FLORES: So a polymer is a fancy name for a plastic, essentially. Pol-- polymer. There are many mers. And the mer is-- is referring to the chemical unit. So polymer is when you take these chemical units and you stack them together. And that'll increase the-- the strength and the-- and the-- the stiffness of the material. .
HOLT: A skier can further tweak the slipperiness of the ski base by coating it with wax - another polymer, which reduces drag by lowering the friction between it and the snow surface.
SCOTT MCCARTNEY (U.S. Ski Team – Alpine): It really makes the water bead up on your ski rather than spread out over the surface area. So it makes the waters' contact point as small as possible so that it's not dragging on your base.
HOLT: Chemists, material engineers, skiers and their wax technicians continue to test new compounds, new polymers for skis used by amateurs, as well as Olympians like 2006 gold medal winner Ted Ligety.
TED LIGETY (U.S. Ski Team – Alpine): Well I’ll test skis almost everyday all season, I’ll have six pairs of skis up there and it’ kind of like formula one where you're tinkering with your suspension or your engine or whatever, we’re always tinkering with stuff from the bindings to the plates to the skis.
HOLT: To set up the skier for a medal-worthy run.
Science Activity (Grades 6-9) from Lessonopoly
THE SCIENCE OF SKIS
Objective: Test the elasticity and slipperiness of two kinds of ski materials to determine what material makes the most elastic and slippery kind of ski?
WHAT YOU NEED
• 2- 400mL beakers or 2 large glasses
• 1 large paper clip
• 1- 15cm (6 in) plastic ruler
• 1- 30cm (12 in) plastic ruler
• 500g weights
• 1 wooden tongue depressor
• 1 wax candle
• Fine (00) steel wool
• Double stick tape
WHAT TO DO
1. The 15 cm plastic ruler and the wooden tongue depressor represent two skis of different material.
2. To make a test for the elasticity of the materials used in making skis, set two beakers far enough apart so as to just support the small ruler suspended between.
3. Bend the large paper clip and hang it on the ruler that is suspended between the beakers at its midpoint. Hang weights from the paper clip and measure the depression by placing the large ruler vertically to the horizontal small ruler.
4. Repeat steps 2 and 3 to test the “ski” that is made of wood by putting the tongue depressor between the beakers.
5. Slipperiness of skis is also very important to make the skier go faster. You can be the skier by using double stick tape and tape the tip of your first two fingers to the top of your plastic ski. Now you can test the slipperiness of your ski by sliding them on the surface of a desk top. Try testing other surfaces such as glass (window), cardboard, etc.
6. Repeat step 5 with a wooden “ski.” You might want to improve the slipperiness of your wooden ski by coating it with wax (rub the side of the candle along the bottom of the ski), or polish the surface of the ski with fine steel wool.
QUESTIONS TO CONSIDER
1. Which material tested more elastic or bendable?
2. Which material tested more slippery?
Explain why one material is better for making the fastest and most slippery “ski.”
One by one the world’s best snowboard jumpers will hurl themselves down a steep ramp, fly off a giant cliff of a jump and — while hurtling through the air — execute sequences of flips and twists so fast and intricate that you’ll need slow-motion replay to even see them happen.
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