I’ve watched bits of the Winter Olympics and been astounded at the death-defying feats of the downhill racers and aerialists, but slowly come to realize that the most fascinating event is the Curling. Known as “Chess on Ice”, precision and skill are paramount to success. Maybe it’s the furious sweeping or the expression of concentration on the faces of the thrower or the pace of the game… I can watch it for ages.

But What Puts the Curl in a Curling Stone?

http://www.icing.org/cgi-bin/archive_reader.pl?URL=game/science/shegelsk

Any curler knows that a curling rock, rotating counter-clockwise (when viewed from above and behind) curls to the left. But to a scientist new to the game, it is surprising. Why so?

Consider an overturned drinking glass sliding over a smooth surface and rotating counter-clockwise: the glass will curl to the left? No, it curls to the right! This may be
surprising to the curler (ed. note: an empty overturned glass may be even more surprising) but it is fairly easy for the scientist to explain.

As the overturned glass slides over the smooth surface, it tends to tip forward.Consequently the front of the glass pushes harder on the surface than the back does. Thus, the friction on the front of the glass is greater than the friction on the back. For a counter-clockwise rotation, the “sideways” motion of the front of the glass is to the left, so the sideways component of the friction on the front of the glass is to the right, and the glass curls to the right. You can easily check this out, and when you do, you will see that the glass does indeed curl opposite to a curling stone.

Why then is the curl of the curling stone opposite to that of the drinking glass? The reason is that the friction on the front of the rock is less than the friction on the back.
How can that be? Part of the explanation is the following. Like the overturned drinking glass, the curling stone tends to tip forward as it slides down the ice, and so the front exerts a greater pressure on the ice than the back. More pressure on the front means that the front of the stone causes more melting (momentarily) than the back. Consequently, the front of the stone will have less friction than the back. For a counter-clockwise rotating rock, the sideways motion at the back will be to the right, and the friction at the back (which is greater than on the front) will be to the left, and bingo, there it is. The rock curls to the left. (See diagram.)

Simple, eh? Well, not quite! If that was the whole story, curling rocks would not curl nearly as much as they do. The friction on the front is not only less than on the back: it is much less, especially when the rock is slowing down, coming over the hog line and into the Free Guard Zone or the house. This explains why curling stones curl most at the end of their motion.

Due to the motion of the rock over the ice, there will be a momentary melting of the ice and the formation of a thin film of liquid just beneath the running surface (contact ring) of the rock. As the rock slides and rotates, the thin contact ring will tend to drag some of the thin liquid film around it as it rotates. There is a force of attraction between granite and water: water tends to cling to granite. Thus, the thin liquid film under the rock tends to get dragged along with the rock.

As the rock slows down, this thin liquid film is dragged around the rock, from the back along the side and eventually to the front. Consequently, the front of the rock will have even less friction on it than the back (as the rock slows down) and that is why we see most of the curl happen near the end of the rock’s travel…

In science, a good model is one where predictions can be tested: our model makes two significant predictions that have been tested and have passed with flying colours.

Our model concerns the motion of a rapidly rotating, slowly sliding curling rock (in curling parlance, a “spinner”). The other concerns the shape of the pattern of contact between the rock and ice.

Suppose you took a curling rock and spun it as fast as you could manage, and pushed it only slightly, so that the rock was rotating very rapidly and sliding over the ice so slowly that it would only move from one side of the house to the other? What would you see?

Our model predicted that because the rock was sliding so slowly, the contact ring would have ample time to drag some of the liquid film around it. In fact, the liquid would be circling around the rock at an appreciable fraction of its rotational speed. The result would be that the frictional forces would change so that friction would stop the rock sliding long before it stopped rotating!

In conclusion, we tested our ideas by predicting specific results, and these were then confirmed by experiments that supported our ideas. Why does a curling stone curl the way it does? Because (1) melting occurs as the rock slides over the ice, and (2) the rock drags some of the thin liquid film around it as it rotates, making the friction much less at the front than at the back of the stone, especially when it is in its final feet of travel.

Ian said:

I’ve watched bits of the Winter Olympics and been astounded at the death-defying feats of the downhill racers and aerialists, but slowly come to realize that the most fascinating event is the Curling. Known as “Chess on Ice”, precision and skill are paramount to success. Maybe it’s the furious sweeping or the expression of concentration on the faces of the thrower or the pace of the game… I can watch it for ages.

But What Puts the Curl in a Curling Stone?

http://www.icing.org/cgi-bin/archive_reader.pl?URL=game/science/shegelsk

Any curler knows that a curling rock, rotating counter-clockwise (when viewed from above and behind) curls to the left. But to a scientist new to the game, it is surprising. Why so?

Consider an overturned drinking glass sliding over a smooth surface and rotating counter-clockwise: the glass will curl to the left? No, it curls to the right! This may be
surprising to the curler (ed. note: an empty overturned glass may be even more surprising) but it is fairly easy for the scientist to explain.

As the overturned glass slides over the smooth surface, it tends to tip forward.Consequently the front of the glass pushes harder on the surface than the back does. Thus, the friction on the front of the glass is greater than the friction on the back. For a counter-clockwise rotation, the “sideways” motion of the front of the glass is to the left, so the sideways component of the friction on the front of the glass is to the right, and the glass curls to the right. You can easily check this out, and when you do, you will see that the glass does indeed curl opposite to a curling stone.

Why then is the curl of the curling stone opposite to that of the drinking glass? The reason is that the friction on the front of the rock is less than the friction on the back.
How can that be? Part of the explanation is the following. Like the overturned drinking glass, the curling stone tends to tip forward as it slides down the ice, and so the front exerts a greater pressure on the ice than the back. More pressure on the front means that the front of the stone causes more melting (momentarily) than the back. Consequently, the front of the stone will have less friction than the back. For a counter-clockwise rotating rock, the sideways motion at the back will be to the right, and the friction at the back (which is greater than on the front) will be to the left, and bingo, there it is. The rock curls to the left. (See diagram.)

Simple, eh? Well, not quite! If that was the whole story, curling rocks would not curl nearly as much as they do. The friction on the front is not only less than on the back: it is much less, especially when the rock is slowing down, coming over the hog line and into the Free Guard Zone or the house. This explains why curling stones curl most at the end of their motion.

Due to the motion of the rock over the ice, there will be a momentary melting of the ice and the formation of a thin film of liquid just beneath the running surface (contact ring) of the rock. As the rock slides and rotates, the thin contact ring will tend to drag some of the thin liquid film around it as it rotates. There is a force of attraction between granite and water: water tends to cling to granite. Thus, the thin liquid film under the rock tends to get dragged along with the rock.

As the rock slows down, this thin liquid film is dragged around the rock, from the back along the side and eventually to the front. Consequently, the front of the rock will have even less friction on it than the back (as the rock slows down) and that is why we see most of the curl happen near the end of the rock’s travel…

In science, a good model is one where predictions can be tested: our model makes two significant predictions that have been tested and have passed with flying colours.

Our model concerns the motion of a rapidly rotating, slowly sliding curling rock (in curling parlance, a “spinner”). The other concerns the shape of the pattern of contact between the rock and ice.

Suppose you took a curling rock and spun it as fast as you could manage, and pushed it only slightly, so that the rock was rotating very rapidly and sliding over the ice so slowly that it would only move from one side of the house to the other? What would you see?

Our model predicted that because the rock was sliding so slowly, the contact ring would have ample time to drag some of the liquid film around it. In fact, the liquid would be circling around the rock at an appreciable fraction of its rotational speed. The result would be that the frictional forces would change so that friction would stop the rock sliding long before it stopped rotating!

In conclusion, we tested our ideas by predicting specific results, and these were then confirmed by experiments that supported our ideas. Why does a curling stone curl the way it does? Because (1) melting occurs as the rock slides over the ice, and (2) the rock drags some of the thin liquid film around it as it rotates, making the friction much less at the front than at the back of the stone, especially when it is in its final feet of travel.

Would that motion on a film of water, leave swirling marks on the ice?

>>Would that motion on a film of water, leave swirling marks on the ice?

Dunno. The ice is “pebbled” by spraying water onto the surface.
I would guess there would be a visible track if you looked closely enough.

BTW.. the sweepers do not melt the ice in front of the stone but raise the temperature enough to enhance the effects explained above.
The more the sweeping the longer the throw and the less the curl.

As an aside not many people know that the Coriolis effect curls the curl the other way in the Southern hemisphere.
A lot of curling experts say that it is the only reason Arthur Allcock never won a curling Gold having been born near Dubbo where most of his curling formative years were spent with legendary trainer Willie McBride.

Peak Warming Man said:

As an aside not many people know that the Coriolis effect curls the curl the other way in the Southern hemisphere.
A lot of curling experts say that it is the only reason Arthur Allcock never won a curling Gold having been born near Dubbo where most of his curling formative years were spent with legendary trainer Willie McBride.

Armless Allcock? Yeah I think I remember him.

Another little known fact is that curling was developed as a way of passing a rope to someone who’d fallen through thin ice on frozen ponds and lakes.

A piece of twine would be tied to the handle of the curling stone, and the stone glided to the person in distress. They’d haul on the twine, whic would have a heavier line attached to it, which, in turn, had a heavier line attached to it.

This rescue method fell out of favour after it was realised that most of the people who needed rescuing were the ones who were doing the scrubbing in front of the curling stone.

Actually, i just made all of that up.

And even more trivia.
The stones come from an islet called Ailsa Craig just off Girvan in Scotland.
We stayed there for a while (Girvan not Ailsa).

Tamb said:

And even more trivia.
The stones come from an islet called Ailsa Craig just off Girvan in Scotland.
We stayed there for a while (Girvan not Ailsa).

So it is.. Girvan, not Ailsa?

roughbarked said:

Tamb said:

And even more trivia.
The stones come from an islet called Ailsa Craig just off Girvan in Scotland.
We stayed there for a while (Girvan not Ailsa).

So it is.. Girvan, not Ailsa?

The stones are from Ailsa the B&B is in Girvan

Tamb said:

roughbarked said:

Tamb said:

And even more trivia.
The stones come from an islet called Ailsa Craig just off Girvan in Scotland.
We stayed there for a while (Girvan not Ailsa).

So it is.. Girvan, not Ailsa?

The stones are from Ailsa the B&B is in Girvan

Don’t you love the science?

> Consider an overturned drinking glass sliding over a smooth surface and rotating counter-clockwise: the glass will curl to the left? No, it curls to the right!

Fascinating. Reminds me of the inverse Magnus effect.

When a soccer ball is rotating counter-clockwise it will swerve to the right. That’s the Magnus effect. But if the spin rate is small relative to the speed of forward motion then it will actually swerve slightly to the left, that’s the inverse Magnus effect.

The Magnus effect, like the sliding glass, is due to simple principles, in this case Bernoulli. The inverse Magnus effect, like the curling stone, is due to boundary-layer effects. The inverse Magnus effect for the rotating sphere results from the differences in the boundary-layer growth and separation along the left and right sphere surfaces.

When a soccer ball is rotating counter-clockwise it will swerve to the right.
————————————————————————————————-

Nope. To the left.

But if the spin rate is small relative to the speed of forward motion then it will actually swerve slightly to the left, that’s the inverse Magnus effect.
————————————————-
Nope. The reverse trajectory is caused by the movement of air inside the ball… not out.