What can fingers brushing against a 40-pound piece of granite do in any event?
This is a fun little physics problem.
The CoF of a curling stone on ice appears to be between .006 and .016 depending on fast its sliding.
So with a CoF of .006 that 40lb chunk of granite has an effective weight of just four ounces relative to that same chunk of granite at a CoF of 1. With a CoF of .016 it’s relative weight is 9 ounces.
So if the finger brush is in either the X or Y axis then basically anything more than what it takes to press a key on your keyboard will have an effect.
Trying to stop the stone from rotating is a whole different matter because then you’re working against it’s stored inertia and that will be much much higher. No way to calculate that though unless you know it’s rate of spin.
I actually don’t believe that any of the accused in this care were intentionally cheating. Honestly it seems damn difficult to make any kind of consistently predictable trajectory change with the touches we’ve seen on video.
Your math and mine both show that a touch can impact the rock but I have to imagine that curling is like golf where you train and hone your swing (release) trying to make it as consistent and repeatable as possible. With that in mind you wouldn’t WANT a touch that mucks with the trajectory of the rock because you couldn’t ever do it precisely and repeatably enough to make it worthwhile.
In my opinion this controversy is happening because some curlers have an ingrained release routine that includes an unnecessary movement / flourish and competitors have decided to make issue of it because it’s getting close to giving a competitive advantage. That’s my two cents for what it’s worth.