Physics of Curling

attempt5001

Muse
A
Joined
Oct 16, 2018
Messages
848
Location
Canada
Not sure if this should be in Sports rather than Science and Math, but I'm looking for some input from some of our resident physics experts pertaining to the sport of curling, specifically how the friction between the rotating stone and the pebbled (bumpy) ice surface causes the stone to curl, and how sweeping techniques can be used to enhance or reduce this effect.

In curling, the ~40lbs stone contacts the ice via a 6" diameter ring of about 1/4" thickness and is rotated clockwise (resulting in a curl to the right) or counterclockwise (causing curl to the left) as it travels down the ice at speeds in the range of 200ft/min.

Considering a clockwise rotation for a moment, the left side of the rock is traveling faster relative to the ice than the right hand side. My thinking (which I would appreciate some critical feedback on) is that the slower moving right hand side encounters a higher drag/inertia ratio than the faster moving left hand side, and that drag pulls the rock to the right. In my mind, this is supported by the observation that as the rocks nears a full stop, the right side become stationary relative to the ice and sometimes "grabs" as it fails to overcome the coefficient of static friction, causing the stone to pivot about the stationary right side.

If that thinking is correct, then the best way to enhance the curl in this scenario would be to sweep the ice on the left side of the stone, thus further reducing the friction on that side and increasing the relative friction between the left and right sides. I would expect this to result in more curl to the right. In contrast, sweeping the ice on the right side of the stone should reduce the difference in drag between the right and left side and cause the stone to travel in a straighter line.

Some will likely suggest a simple experiment to check and see, which I will definitely attempt, but the high number of variables (including subtle changes to the ice after a rock has traveled down it with or without sweeping, and variables in delivery line and speed and rate of curl, as well as sweeping pressure, control, pace and consistency) and the subtlety of the effect make it challenging.

I'd love to start with a sound hypothesis based on the physics and fine-tune from there. Thanks.
 
Last edited:
Minor point - your '200ft/sec.' is very wrong. About 6'/sec at the point of release is more like it.
 
What do top class curlers say about this?

When we’ve solved this problem, perhaps we can address the issue of reverse swing in cricket :-)
 
hecd2 said:
What do top class curlers say about this?

When we’ve solved this problem, perhaps we can address the issue of reverse swing in cricket :-)
Click to expand...

Both the underlying physics and the best sweeping approaches are hot discussion points in the top end of the sport right now. I coach at a competitive youth level so am working with my team to see what works best, but confirmation bias is hard to avoid.
 
Wild generalised guess - it's much the same mechanism as a tennis ball hit with topspin, that dips in flight more than a 'flat' hit.

One side of the stone/ball is dragging material (ice particles or air) in front of half the stone/ball. while the other side is dragging stuff away. The stone reacts by favouring travel in the direction where it's experiencing less friction from the particles.

Sweeping can either remove or add particles, depending on the nature of the sweeping, thus affecting the stone's route. I guess if you want the stone to slow in the general sense then you push ice in front on both sides.

(Something like that)

eta: So I googled it and my theory is not much use :)
 
Last edited:
Sweeping particles into the path of the stone to slow it down would be unconventional thinking for curling for sure.

I'm not sure about your idea that the object moves in the direction it experiences less friction. I think it's the other way around, at least at certain speeds.

Consider a ball flying through the air just above water. If it touches the water it encounters much higher resistance on that side. If it's going very fast, it might skip or glance off in the other direction, but at lower speeds, it will dig in hard towards the friction. A curling stone touching a soft spot in the ice will do the same.

That's why I think it's helpful to reduce the friction on the outside running edge to make the stone curl towards the inner edge.

Appreciate the discussion though and efforts to explain if my thinking is wrong here.
 
Last edited:
At the moment we don’t seem to have a repeatable and predictable phenomenon so far as sweeping and the resulting curve goes. Don’t we need that before we can have a theory to explain it.
 
hecd2 said:
At the moment we don’t seem to have a repeatable and predictable phenomenon so far as sweeping and the resulting curve goes. Don’t we need that before we can have a theory to explain it.
Click to expand...

Well, we have a repeatable and predictable phenomenon in that the stone curls right with a clockwise rotation and left with a counterclockwise one. We also know that sweeping the full slide path reduces the friction and causes the rock to travel further.

It seems reasonable that if we understand those phenomenon well and the theory behind them, we could fine-tune the sweeping for more focused effect.
 
So it might be that the sliding friction is speed dependent in which case the force due to friction will be asymmetric left to right. What is the relationship between the radius of the curve and the rotational speed?

ETA: if it’s a friction thing and you can confidently say that sweeping reduces friction, then sweeping the outside of the curve should reduce the radius - tighten the curve.
 
Last edited:
Yes, I think that makes sense too. There is also a shift in the typical rotation speed in the game right now. It used to be a draw (stone thrown just fast enough to come to rest I'm the middle of the rings) would rotate about 3 times from release to rest. Now some teams are going with 5-7 rotations. This tends to lead to a more predictable and slightly less curve overall. Things change again if you start to spin the stone even faster with some really huge, late curling action if you spin it very fast.
 
The Great Zaganza said:
I'm happy to believe that it's the result of a pact with a witch.
Click to expand...
I see your point.
51318022230_c2975b183d.jpg

53540746026_34fa09a725.jpg
 
attempt5001 said:
Now some teams are going with 5-7 rotations. This tends to lead to a more predictable and slightly less curve overall.
Click to expand...
Hmm - that goes against the idea that it is a left to right asymmetry. Naively, the curve should get tighter the faster the spin, for low spin rates anyway. Assuming by less curve, you mean larger radius?

There's also the possibility that the cause is a front to back asymmetry. The front of a clockwise spinning stone is pulling right and the back is pulling left looking in the direction of travel. The asymmetry would arise from the fact that the back is crossing ice previously "swept" by the front a moment earlier. If that is the cause of the curve, I don't think sweeping to the left or the right would affect the radius very much.

I think you are going to have to do some tests controlled as well as you can to test these various ideas. I don't think anyone can do other than speculate naively on the underlying physics without more experimental data.
 
That's a good point. I had definitely been focused solely on the sides rather than the front and back (and all the points in between). A more complex situation than it seems on the surface for sure.

I'll keep watching what the pros are doing and saying and try to set up some experiments myself as well.

Cheers!
 
My memory is that the stone curls more as it slows, and that sweeping not only makes it run further but also curl less. Recollections of frantic sweeping not only to make the stone run further but to stop it curling too early, or the inverse; holding off until it curls enough then frantically sweeping to keep it going straight in its new direction.

I had always imagined it as the momentarily melted patch under the contact ring freezing in tiny patches and grabbing at the stone, slowing it, and that this would happen proportionately more on points which were travelling slower. I rather assumed someone would have worked it all out and there would be no mystery remaining.
 
Last edited:
Smarter Every Day did a video on it.... 9 years ago???


I don't remember if that one was talking about the info in https://www.sciencedirect.com/science/article/abs/pii/S0043164813000732?via=ihub (from 2013).

My memory is that there have been several studies since, none with explanations that have garnered universal support as being correct.

cf: https://www.nature.com/articles/s41598-020-76660-8 and https://cdnsciencepub.com/doi/10.1139/cjp-2016-0466


Basically, if you want to come up with a simple model of how this works, it will be incomplete. It might be coincidentally useful for your purposes, but it will not explain other known details.
 
Last edited:
You must log in or register to reply here.

Back
Top Bottom