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February 26, 2008
Drag Effect on Curling Rocks
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---- First, watch the video a few times so that you see the setup of the rocks in the house, and also the shot that Jennifer Jones plays: I've enlarged one frame of video to show the setup and alignment of the rocks in the house. I've also drawn blue arrows, showing the path that the yellow rock should have normally taken if it wasn't frozen with the struck rock:  The green arrows show the path that the struck red rock will take. Since these two rocks are indeed frozen, as the red rock starts to move down this path the striking band of the red rock "grabs" the striking band of the yellow rock through friction and applies a force on the yellow rock in the direction of the green arrow. To figure out why the rock ends up going a completely different direction than either the green or blue arrows indicate, all we need is some high school physics: the addition of vectors.  A vector represents both the magnitude and direction of force. I have attempted to draw the green and blue vectors to scale. Moving the green vector so that it is head-to-tail with the blue vector, the result is the yellow vector. Of course this is all manufactured by me to work out correctly, but you get the idea. Curling rock drag effect is something that they talk about on television far more often than I've actually ever seen it (I suppose it's something else for the commentators to mention). Or perhaps the drag effects just weren't as obvious and pronounced as in the video clip above. Next week I'm going to set up a few practice situations and try to simulate the drag effect by myself. I'm not sure that I'll ever see this effect myself in a real game, but at least now I'm convinced that it's physically possible! Posted by Hammer at February 26, 2008 12:02 PM |
I had been hearing about the "drag effect" or "drag theory" of curling rocks on television for a few years, but up until last week I had never truly seen a clear example of it. Now I have, and here's the video and an explanation of what's going on.If you enjoyed this article, you may want to read more in the Curling category.
Comments
@johnston: yes, look here:
http://www.nrcresearchpress.com/doi/pdf/10.1139/p03-066
Hello Hammer,
Could you link me to the paper by Mark Denny. I am interesting in reading it.
Johnston
Great video. To folks who don't believe this is the drag effect, setup that situation with billiards balls. In billiards, it in fact doesn't matter where you hit the top red rock, the yellow rock will always come out of the collision at the exact same angle. (Along the path of the blue arrows)
If this collision could be described purely by vectors, then you would have an identical path of movement with curling stones and with billiards balls. Turns out not to be the case. It is the striking bands in the curling stones that allow the yellow rock to move more or less straight backwards, and this is a fantastic demonstration of that.
I've used this effect last year, quite handy if you have a basic understanding of how it works. I hear many skips say "Just hit it anywhere, it will go", which this particular example shows isn't true. The angle at which you hit the rock is very important, as it will determine the degree in which your rock will drag.
And one reason why this is indeed drag, and it's clearly visible in this video: Look at the yellow rock's degree of rotation. It's spinning like crazy, something that a "normal angled collision" from the red rock would never have achieved, at least to this degree.
Nice shot by Jennifer Jones, good explanation on the mechanics. Thanks :)
David Murdock used the drag effect to win the TSN Skins game on his final shot agaist Ferby. There is no way those rocks end up where they did without the "drag effect"
Thanks for the detailed explanation! It makes sense now.
I don't agree with Don's comments, I think it is drag effect.
This has nothing to do with drag effect, it's simple collision physics. The vector description is wrong in the diagram. If you do a proper vector analysis you will see that the rock ends up where it should. The top red rock doesn't move straight back but moves at aprox 30 degree angle when struck by the shooter. You would get the same effect if the top red rock was thrown from (aprox) the hog line over against the boards.
In other words you have to do two vector analysis, first the direction of the top red rock, then the direction of the yellow rock when struck by the red that is now moving at an angle from left to right.
Loved the analysis, terrific explanation. We were trying a few practice shots last week and couldn't get it to work. So not high percentage unless you are Jennifer Jones or Kaitlyn Lawes (used in 2008 Canadian Juniors) I guess. Will try it with the same set-up on the centre-line though may work better...
Although I find your explanation interesting, I would like to find why the effect works even when the rocks are not completely frozen together. I was told by a national level coach (and I have personally witnessed it) that some drag effect can be present with a 2 inch rock separation, some literature even mentions 4 inches. What makes the friction on the band different when it is hit by a stone that starts its movement 2 inches away instead of 2 feet away?? Kinetic mystery...
Hello Daiyo,
No, I had never seen vectors being used to curling analysis before, and it took me a while of thinking about this to come up with the explanation. However, after doing some searching in Google, yes others have used models like this in the past, so I'm not the first. For example, Mark Denny wrote a scientific paper in 2003 that uses vectors to explain curling rock motion.
- Hammer
Impressive example of the drag effect. Even more impressive is your explanation using vectors. Seems to me vectors may be a powerful tool for analyzing other aspects of shot-making (or of the delivery more generally). Would you agree? Are you aware of any other use of vectors in curling?