Slip and Slide

Slip and Slide: Ice, the Winter Olympics, and Animal Adaptations.

Ice ice baby! One of the most fun memories I have of winter is pretending to ice skate by sliding on the ice in my shoes. If you were careful and kept your balance you could zoom down the street like magic! Other times, I would slip and fall right into the snow!  Have you ever wondered about the slipperiness of ice? Other solid things don’t have this slick property, so how come ice does?  With the Winter Olympics coming up it is fun to explore the world of ice both through sport and through animal adaptations!

Turns out that ice is very special because of the molecular properties of water.  Remember that solid water (ice) is one of the few solids that is less dense than its liquid state.  Also, water’s freezing point is very close to what is known in chemistry as the triple point.  The triple point is a where a substance exists in multiple phases at once.  So, if you take your foot and apply pressure to the ice it may melt ever so slightly creating a liquid layer on top.  This means that ice has little friction, so sports on the ice and snow must compensate.  In some cases, such as downhill skiing, they reduce friction even further, but in others such as cross-country skiing, you add friction to create propulsion.  Even more interesting are sports such as curling that manipulates friction in many ways to send a rock down the ice to hit a target.  Many different animals have also adapted to slipping and sliding along the ice!

Sliding on Ice: Curling

One of the sports in the Winter Olympics I’m most intrigued by is curling.  It looks simple and yet the physics of this sport is both complex and fascinating.  Each team member, from the skip to the sweepers plays a role in guiding this big rock down the ice to the house where the target is.

Curling has been around since 16th century Scotland and gets its name from the slow gentle curve the stone makes as it slides down the ice.  It became an official Olympic sport in 2002 and consists of 2 teams of 4 throwing 8 stones each.  They go 8-10 rounds and compete for points.  Curling stones are made of granite, which is hydrophobic, and come from a quarry in Scotland.

Beyond the handle, the curling stone has two important features: the running band and the striking band.  The running band is a sharpened ring on the bottom of the stone, which reduces contact with the surface. It is the rotation and pressure from this running band that manipulates the friction under the stone and helps it glide down the ice. The striking band is the smooth outer edge of the stone and its purpose is to allow for transfer of energy from one stone to the next, so you can knock your opponent off target!

I honestly always thought the sweepers were adding friction, so the stone didn’t soar past the target, BUT it is actually the opposite.  Also, curling ice is different in that it is pebbled.  Tiny droplets of water are sprayed onto the surface where they freeze to create a textured surface.  They slice the tops off each tiny ice bump and ta da you’ve got perfect curling ice. This results in less friction because less of the rock is touching the ice.  The purpose of sweeping, as I discovered, is to further reduce the friction by creating tiny scratches in the pebbled ice.  This decreases the amount of ice sliding under the running band even more. Sweeping helps the rock go straighter and further.  It is one of the few sports where once thrown the team can adjust and manipulate the trajectory of their object.

Tobogganing Emperor Penguins:

In the animal kingdom sliding on ice immediately makes me think of penguins sliding around on their bellies. The emperor penguin is both the tallest and heaviest species of penguin and has several adaptations that help it survive the harsh weather of Antarctica.  They have a lot of blubber to stay warm especially during the long winter, but one of the drawbacks to this adaptation is that it makes them very unbalanced and gives them a lumbering waddle.  So, what do they do if they have to move quickly while on the ice? They toboggan!

Tobogganing is when the penguin slides on his stomach.  His slick waxy feathers offer little friction against the ice and the penguin can slide off and away if a sea leopard comes up on the ice.  Their target when trying to escape is almost always the ocean.  Once in the ocean emperor penguins can go nearly 8 mph and can stay underwater for around 20 minutes.  They can also compress air in their feathers and use it to propel themselves twice their speed, so they can shoot out of the water and up onto the ice.

Speeding over the snow: Cross Country skiing

So, what about snow?  Snow is made up of tiny ice crystals but is fluffier – you can slip on it, but mostly you just get stuck in it – unless you have the right equipment! Cross country skiing is the oldest form of skiing and emerged from a need to travel over snowy terrain.  It was developed into a sport at the end of the 19th century and was added to the Olympics in 1924 (men) and 1952 (women). Traditionally this Olympic sport is dominated by the Nordic countries.

In cross country skiing you rely on your own locomotion for propulsion versus using gravity to zip down a mountain like in downhill skiing. The motion of cross country skiing is very different from downhill.  The boot is attached only at the toe, so the heel goes up and down as the skier strategically uses friction to glide forward.  As you put pressure down on one ski you gain traction from the grip zone and can glide forward on your other ski.

The classic stride is alternating pressure on your skis like this on prepared parallel tracks.  There is also the skating stride, which is shorter, and faster.   The skier is propelled on a smooth, firm snow surface by pushing your skis alternately away from one another at an angle, in a manner similar to ice skating.  As you can imagine the skating stride looks a little crazy, but is super effective in a race.  Look for this when you watch the Olympics!

Both strides take advantage of the increased surface area of the skis to prevent the skier from sinking in the snow.  Well before humans strapped on skis, animals adapted to run on and over the snow.

Predator and Prey: Snowshoe Hare versus Canada Lynx

The snowshoe hare and Canada lynx both have adaptations that allow them to move quickly over snow.  As with most predator prey relationship their survivals are interwoven.  The Canada lynx’s population parallels that of the snowshoe hare since it is its primary source of food.  So how do they match up in the snow?

Snowshoe hares have larger hind feet and lots of fur between its toes compared to other hares.  This means its hind feet act like snow shoes allowing it to quickly move over the snow.  A snowshoe hare can run nearly 30 mph over the snow and can jump 10 ft in a single bound.  This is helpful as it escapes its main predator the Canada lynx.

Snowshoe hares are the main prey of this small cat, which also has special snow adaptations.  Their feet are oversized with extra fur, which gives the Lynx its own pair of snowshoes!  Since the hare is faster than the lynx, the lynx relies on ambush for success and can silently stalk prey in the snow thanks to its snowshoe feet.

It is amazing how both humans and animals have adjusted to getting around in the ice and snow.  From sliding rocks and penguin bellies to skis and “snowshoe” feet, the ice and snow is a fun arena in which to compete.  I don’t know about you, but I cannot wait to watch the Winter Olympics this year – especially curling!

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