I suspect that the reason curling stones curl the way that they do is primarily due to one side of the stone being subjected to “static” friction while the other side experiences “kinetic” friction. This would also explain why the curling doesn’t start to happen until the stone’s linear velocity has sufficiently decreased.
If a stone is moving down the ice, away from the observer, and spinning to the left (that is, counter-clockwise when looking down on it), the right-side edge of the stone is moving in the same direction that the stone travels while the left-side edge of the stone is moving in the OPPOSITE direction that the stone travels. This means that the right edge of the stone is moving faster across the ice than the stone’s linear velocity. And the left edge of the stone is moving slower across the ice than the stone’s linear velocity.
As the stone’s linear velocity decreases, there will come a point when the left edge of the stone is no longer moving relative to the ice, while the right edge of the stone is still moving at 2 times the stone’s linear velocity relative to the ice. This means the left side of the stone is now being subjected to static friction while the right side is only being subjected to kinetic friction. The force opposing the left side of the stone is greater than the force opposing the right side of the stone, causing the stone to pivot around the left edge of the stone, “curling” to the left, until the stone's linear velocity reaches zero.
That does in fact sound like a reasonable hypothesis. But you have to account for why a beer bottle or an upturned glass sent spinning down a table curls in the opposite direction; i.e., why is it different for a curling stone? Also, why won't a stone curl if the ice is not pebbled? Your hypothesis should account for that too.
By the way, I think you got downvoted earlier because you started off with the words "the solution is simple", sounding extremely sure, rather than saying you have a theory.
I wasn’t too surprised about getting downvoted. I suspected that some might find “the solution is simple” a bit brazen, but I wasn’t sure how old the thread was, and wanted to draw some attention and critique before the thread died. My next line was more honest “I suspect that the reason…”. :-)
As for why a curling stone is different than a beer bottle or upturned glass on a table, that wasn’t the goal of my thinking. I was only trying to explain the curling stone. In any case, while having some similarities, the two scenarios are still pretty different. As laxd points out below, the beer bottle and glass have higher centers of gravity which make the “leaning forward” line of thinking seem more reasonable.
As for the effect of pebbled ice, it seems reasonable that the difference between the static friction coefficient and kinetic friction coefficient is greater for pebbled ice than for smooth ice. And if static friction and kinetic friction are approximately the same for smooth ice, then this effect would not contribute substantially to curling on smooth ice.
This was a fun problem to think about. I had hoped that a smarter physicist would tell me why my hypothesis was bogus. As a friction expert, Nyberg almost certainly entertained this idea at some point. I may send him a message to see what it is that I’m missing.
The beer bottle case is explained in the article:
"Take a beer bottle or an upturned glass and send it spinning down a table: if it rotates to the right, clockwise, it will curl to the left; if it rotates to the left, it will curl to the right. That’s because the bottle, as it moves forward, also tips forward slightly, adding weight to the leading edge. More weight means more friction."
I guess a heavy curling stone with a lower center of gravity and on a slippery surface would'nt tilt forward like a bottle.
Came back to this thread to see if someone had written an enlightening rebuttal of GP rather than downvoting him.
I suspect that the reason curling stones curl the way that they do is primarily due to one side of the stone being subjected to “static” friction while the other side experiences “kinetic” friction. This would also explain why the curling doesn’t start to happen until the stone’s linear velocity has sufficiently decreased.
If a stone is moving down the ice, away from the observer, and spinning to the left (that is, counter-clockwise when looking down on it), the right-side edge of the stone is moving in the same direction that the stone travels while the left-side edge of the stone is moving in the OPPOSITE direction that the stone travels. This means that the right edge of the stone is moving faster across the ice than the stone’s linear velocity. And the left edge of the stone is moving slower across the ice than the stone’s linear velocity.
As the stone’s linear velocity decreases, there will come a point when the left edge of the stone is no longer moving relative to the ice, while the right edge of the stone is still moving at 2 times the stone’s linear velocity relative to the ice. This means the left side of the stone is now being subjected to static friction while the right side is only being subjected to kinetic friction. The force opposing the left side of the stone is greater than the force opposing the right side of the stone, causing the stone to pivot around the left edge of the stone, “curling” to the left, until the stone's linear velocity reaches zero.