the olympics: canadian rock stars

minipost

Growing up in North Central Montana, I spent a fair amount of time in Southern Alberta.  One of the things you did with friends was curling - the only regular sport I can think of where a projectile's path is modified on purpose after launch.  Imagine tennis or volleyball where an essential part of the game is having another player offensively or defensively modify the path of the ball..

So let's try a little physics experiment. The rock has a mass of about 20 kilograms with a thin ring on the bottom that contacts the ice.  You'd think you could model this as an upside down glass tumbler moving across a low friction surface.  Give it a try.  Turn a glass upside down and give it a shove with a bit of spin on a smooth surface like a table.   You'll notice it veers in the direction opposite the spin and the amount of veering is related to the rate of spin.  So what's going on?

Take a  counter clockwise spin.  At the front of the glass the motion of the spin is to the left meaning the opposing force of friction is to the right.  At the back of the glass the motion of spin is to the right, so the force of friction is to the left.  If they were equal the glass would go straight, fall of the table and shatter into shards.  But the forces aren't equal.  The glass tips forward a bit putting more force on the front.  As a result the force of friction at the front of the glass is to the right and larger than the force of friction at the rear, which is to the left.  You add these forces and find a net force to the right so the glass moves somewhat to the right before flying off the table and crashing to the floor.  The diagram is for a curling rock and there's a discrepancy, so read on.

A counterclockwise spinning curling rock veers left!  

There are two main hypothesis and reality is probably a combination of the two plus a bit more.  I'll use what I think is the strongest contender.  The higher pressure on the front of the tilting rock differentially melts the ice at the front more than the back creating a slightly slipperier surface at the front.  The force of friction at the front (to the right in our case and properly shown in the illustration) becomes smaller than the leftward frictional force in the back.   Add the forces and the rock veers to the left.  (I'm leaving out quite a bit, but that's the gist)

There are some curious reasons why this can happen. The special pebbling of the ice surface is critically important and ice conditions vary favoring players with a lot of experience.  The brooms?  They have nothing to do with clearing off the ice, rather they heat it a bit making the it a bit slipperier causing a straighter trajectory.

Played properly it's a beautiful sport.  The game has great depth and innovations like smart brooms are revolutionizing technique.   Experience is critical and often the Canadians show the way with the best deep understanding of sheets of ice.

 

Comments

[Jean M Russell]

Fantastic. How delightful to imagine.

[Dan Bartholomew]

What are the differences between a game and a sport?

And to which category(ies) does curling belong?

[Steve]

People draw differing lines. As an example I wouldn't classify esports or chess as sport -even through skill is involved. They're games. For it to be a sport my personal definition requires some athletic performance in addition to skill. I've tried curling -- at the high end there is some athleticism, although not at the level I tried. Certainly not a lot compare with other athletic sports, but it passes the line for me.. at least in the Olympics. Probably not for other people.