Why do Curling rocks curl? Scottish glaciologists diss Canadian physicists

[Northern_Piper]

Now here’s a true great debate, one that doesn’t involve either Frat-Boy or Flip-Flop Man.

Why do curling rocks curl the way they do? If you give them an in-turn (i.e. - clockwise turn), they curl to the right, whereas most round items spinning clockwise will curl to the left.

Two teams of scientists, one Scottish and one Canadian, have recently published competing theories. They both agree that it’s caused by the friction of the rock melting the ice as the rock travels, but from that point, it gets nasty. The Canadians say it’s because the friction melts the ice at the front of the rock; the Scots say it’s because the friction melts the ice at the sides of the rock.

A simple disagreement? Well, in the polite world of scientists, there’s some considerable dissin’ going on, as reported in the Times:

Mark Shegelski, professor of theoretical physics at the University of Northern British Columbia, has produced a complicated mathematical formula to prove his theory that the front edge of the curling stone is lubricated by a microscopic slurry of water and ice caused by friction. The liquid layer means there is less friction at the front of the rock than at the back, making it curl in the direction in which it is spinning.

However, a rival theory put forward by Dr Brett Marmo, a glaciologist at Edinburgh University, claims that the secret lies not in the front or back of a curling stone, but its sides.
…
Shegelski is adamant that his “wet friction” theory, based on 10 years of research, is correct, but Marmo describes his formula as “really ugly” and his reasoning “over-complicated”.
…
“Our work makes a very convincing case that melting is inextricably involved,” said Shegelski. “To explain our experimental results without invoking the existence of a thin-liquid film, well, I would be shocked if somebody came up with a successful theory that involved no melting.”

While Marmo accepts that melted ice is involved, he is dismissive of the Canadian paper, The Motion of Curling Rocks: Experimental Investigation and Semi-phenomenological Description. “I don’t believe this explanation,” said Marmo, who received funding from the Scottish Institute of Sport to carry out his research.

“Have you tried to read it? Speaking as someone in the game, I found it incredibly technical. I’m a glaciologist and have spent my life looking at ice, snow and friction. Whereas these guys are pure physicists.

“My theory is quite simple compared to theirs, which doesn’t explain why there is much more water at the front than the back — the mechanism isn’t explained properly.”

Scottish glaciologists v. Canadian physicists; curling; rocks being thrown, both in reality and metaphorically; and the age-old question of why rocks curl - now this is a debate for the ages!
[Note: the Times got the details a bit wrong - they seem to assume that a curling rock always spins clockwise, and curls right. That’s an in-turn, as any country curler on the Canadian prairies knows. There’s also the out-turn, which makes the rock spin counter-clockwise and curl left.]

[Left_Hand_of_Dorkness]

My guess is that they curl to the right because they’re part of the UK and as such support Bush’s backward policies.

Daniel
d&r

[Ike_Witt]

@Northern Piper

Why do curling rocks curl the way they do? If you give them an in-turn (i.e. - clockwise turn), they curl to the right, whereas most round items spinning clockwise will curl to the left.

Is that true? I haven’t played shuffleboard in a while. Does there need to be friction? Frisbees have a huge amount of spin but can travel in a straight line with no problem.

[chappachula]

@Northern Piper

Now here’s a true great debate.]

If this were in GQ, I’d wait for the reactions of the glaciologists and phsyicists.But since we’re in GD territory, let’s get straight to the real issue:

Why the hell is curling a sport?
Why not just sweep your kitchen floor over and over again?

I just don’t get it. How did this start?It’s minus 50 degrees outside and bored kids are looking for fun. “Hey, guys, I know what we can do–let’s sweep the ice! Then we can help mom clean the house”.
Maybe living up north causes brain cells to die of frostbite.
note to mods: I know the rules in GD–but I couldn’t resist. Sorry. I won’t do it again.I promise

[Squink]

“To explain our experimental results without invoking the existence of a thin-liquid film, well, I would be shocked if somebody came up with a successful theory that involved no melting.”

Surely someone has set up a curling rink on that plastic “artificial ice” by now. Do the stones curl without melting or not?

[Grey]

@chappachula

I just don’t get it. How did this start?It’s minus 50 degrees outside and bored kids are looking for fun. “Hey, guys, I know what we can do–let’s sweep the ice! Then we can help mom clean the house”.
Maybe living up north causes brain cells to die of frostbite.

Winning team buys the first round.

Oh and the rink keeps the beer cold while you’re throwing.

[Gorsnak]

@chappachula

Why the hell is curling a sport?
Why not just sweep your kitchen floor over and over again?

This is cliche, but in this case perfectly applicable…don’t knock it till you’ve tried it. Curling is a lot of fun, far more than the uninitiated might expect. It’s just inexplicably satisfying to heave your rock down the ice to smash into other rocks. It’s also something most anyone can participate in, and something where it doesn’t matter too much if you really suck. And that’s before we even get to the beer part.

At the top end of the sport, it’s very, very competitive, and the better rink wins a very large portion of the time. Perfect execution and perfect strategy are required, and very, very hard to attain. At the small town bonspiel level, there’ll be a few competitive rinks, and a bunch of people just out having a blast, where it doesn’t matter if you don’t get your opening draw past the hog line, or completely miss that open takeout. Sure, people will make fun of you for messing up, but curling being as tough to be good at as it is, they’re likely to throw a few bad rocks the next end, and then you can make fun of them. And crack open another sixpack.

[scotandrsn]

@adam yax

Is that true? I haven’t played shuffleboard in a while. Does there need to be friction? Frisbees have a huge amount of spin but can travel in a straight line with no problem.

Curling (otherwise known as the emperor of pasttimes) is called such because the path of the stone “curls” when it is given a very slight spin upon release (we’re talking like 2-3 RPMS here.

Curling is great fun by the way, particularly in the fact that you get to slide around the ice on teflon-soled shoes, which is way funner than skating. It’s a game of inches, which does not lend itself to macho posturing, although you can’t put that past the Canadians.

If you spin the stone too fast, it will not curl at all. It must be very subtly handled. It takes quite a bit of practive before you can “bend it like Benshoof”.

[Ike_Witt]

@scotandrsn

Curling (otherwise known as the emperor of pasttimes) is called such because the path of the stone “curls” when it is given a very slight spin upon release (we’re talking like 2-3 RPMS here.

Curling is great fun by the way, particularly in the fact that you get to slide around the ice on teflon-soled shoes, which is way funner than skating. It’s a game of inches, which does not lend itself to macho posturing, although you can’t put that past the Canadians.

If you spin the stone too fast, it will not curl at all. It must be very subtly handled. It takes quite a bit of practive before you can “bend it like Benshoof”.

I know curling. I am Canadian. I lament the fact that ESPN shows poker but not the Labatt Brier.

[Emperor_Penguin]

] Mark Shegelski, professor of theoretical physics at the University of Northern British Columbia

Hey! That’s my school!

Sorry, this impresses me. My town in small and in the north. Biggest thing for about 400 km in any direction. Our total population? 80,000 Our school population is about 3500 students, including grad students. In my first year, I was on a first name basis with most of my profs. Nice to see that we are actually being noticed. Go Mark.

And curling is an amazing game. It takes a high level of finesse. I’ve been trying to get ateam together this year, but no dice.
[sub]What was the debate again?[/sub]

[BobLibDem]

I have two theories.

Imagine you are a curling stone and you’re heading down the ice and you’re spinning counterclockwise. From your point of view, the ice is pushing against your motion. Looking at your left side, the stone itself is moving from right to left or in the same direction that the ice is pushing you. Looking at your right side, the stone again is moving from right to left but in the opposite direction of what the ice is pushing. Since the left side of the stone is offering less resistance to the ice’s force on it (since the spinning of the stone means the relative velocity of the stone to the ice is less on this side than the other), it will tend to move in the path of least resistance, i.e. to the left.

Second theory:
The stone starts off with counterclockwise angular momentum. Friction of the ice slows it, but it wants to conserve this rotational momentum by revolving about a fixed point. To create counterclockwise momentum, the point must be to the left and the stone curls in that direction.

[scotandrsn]

For any non-curling afficionados participating, it should be known, in case it factors into your analysis, that a regulation curling sheet (the stretch of ice you play on) is not Zamboni’d down to a sheer surface. It is noticeably, although not too significantly, rougher than competition skating ice, so that the stone has a better chance of actually stopping in the target area.