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03-27-14 06:40PM |
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Flat Hat
Harvey Hacksmasher
Registered: Mar 2014
Location:
Posts: 86 |
quote: Originally posted by ChiefIceMinion
For "fresh" ice, my understanding is that the pebble is still rough from whatever nipping, clipping or rock running was done prior to the start of the game, so the sweeping smoothing out the pebble would have the same friction-reducing effect by erasing the roughness of the pebble.
I would think that if the broom heads were scratching the ice in a manner that would increase the curl of a stone, we'd have already seen "observational" evidence (someone's in game experience) of this occurring. However, based on the "accepted wisdom" that all sweeping straightens out a rock's path, either current broom heads smooth (but not scratch the ice OR that the scratches are significantly wider/deeper than the running surface texture, reducing running surface contact and thus curl.
Chief Ice Minion
I would just mention that not all rocks need to be swept, and remind folks of the days when you could lean on your hog bristle broom with the face of the broom clearing the path of the stone... banned because it was too effective, leaving us with sweeping across the face of the stone.
Did they ever test the emory scratches with a normally thrown handle? (4 turns or so) Did the rock curl more or less depending if it was with or against the angle of the scratches?
Knowing now that the purpose of the study wasn't to determine why curling stones curl, but to determine the effect of scratches on the ice acting on the stone, I am left wondering if this is a case of having only a hammer, all problems start looking like nails. Er, scratches.
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03-28-14 10:05AM |
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RockDoc
Swing Artist
Registered: Apr 2005
Location:
Posts: 399 |
quote: Originally posted by Unregistered
Yes and for many a year, humans thought the Earth was flat. Challenge conventions my friend! Especially with something that conventional physics has failed to explain to date! You (the physicist) say it can't happen, I (the layman) say that it can? Until we prove it, who's really right? Probably the physicist but we still don't know!
You can believe what you like, but you may not like the results. A forward vector can't generate a left-right force an any system of mathematics, and 2+2 still equals 4. And while we once believed the earth was flat, no one would seriously challenge the thesis that is is not based on our current level of information and understanding.
Science doesn't PROVE anything. Science EXCLUDES what can't work, and the residue of what is not excluded, after many, many attempts to exclude it, becomes increasingly probable. Scientists challenge conventions all the time, but some conventions are so robust that the probability of them being wrong are exceedingly remote. Theories that have withstood the test of time, and can be successfully used to predict other successful hypotheses and physical observations are regarded to be highly reliable explanations of how the world works. Some "opinions" carry more weight than others. In the field of mathematics (e.g. vectors) many things can be proved and are reduced to certainties. The likelihood that after 500+ years of study that we have somehow "missed" some basic precepts of Newtonian mechanics is simply not credible.
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03-28-14 04:23PM |
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toeslider
Harvey Hacksmasher
Registered: Mar 2005
Location: Alberta
Posts: 18 |
quote: Originally posted by RockDoc
You can believe what you like, but you may not like the results. A forward vector can't generate a left-right force an any system of mathematics, and 2+2 still equals 4. And while we once believed the earth was flat, no one would seriously challenge the thesis that is is not based on our current level of information and understanding.
Science doesn't PROVE anything. Science EXCLUDES what can't work, and the residue of what is not excluded, after many, many attempts to exclude it, becomes increasingly probable. Scientists challenge conventions all the time, but some conventions are so robust that the probability of them being wrong are exceedingly remote. Theories that have withstood the test of time, and can be successfully used to predict other successful hypotheses and physical observations are regarded to be highly reliable explanations of how the world works. Some "opinions" carry more weight than others. In the field of mathematics (e.g. vectors) many things can be proved and are reduced to certainties. The likelihood that after 500+ years of study that we have somehow "missed" some basic precepts of Newtonian mechanics is simply not credible.
I’m not sure that anyone is suggesting that something in the field of physics has been “missed”, but that maybe we are too quick to exclude an idea because of “what we already know”. I find it very hard to not find some merit to the “fast side vs. slow side” approach to an answer, particularly since slower rocks curl more and the rocks tend to curl more as they slow down when the differential between the fast side and the slow side, relative to forward travel, would be the greatest.
My degree is not in physics, so my approach is from a different angle and my terminology is probably not approved, but there are 2 things that I can observe from experimentation:
- in the case of a vehicle on ice with tires spinning, the tire spinning slowest will have better traction. It is not necessary for the tire to have complete purchase of the surface (or “sticking”’ using terminology from someone’s prior post) to observe that the tire spinning slower has superior traction
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- corner sweeping works. If you sweep only one side of the future path of the running surface you can affect the travel of the rock. If the rock is not spinning excessively, by sweeping the “inside” of the curl you can actually change the direction of rotation. Any driver training instructor will tell you that warmer ice is worse for traction with a vehicle, so, by sweeping we are warming the ice and decreasing the available traction.
How all of this would translate into friction forces and vectors I would have to leave to someone that does have a physics degree, but could the braking caused by more traction on the slow side have an influence by effectively causing there to be a different forward vector for the slow side compared to the fast side? Alternately, could the friction on the slow side, as it moves from the point of maximum traction (presumably 6 or 9 o’clock depending on direction of rotation) to the point where it loses traction, cause the vector in the necessary direction since this would be in the bottom hemisphere of rotation?
Being that the lateral motion is 3 to 4 feet compared to the 100 to 120 feet of forward motion we are only looking for a very small force, or differential between forces.
The line to call me an idiot starts here >
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03-28-14 04:32PM |
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Unregistered
Guest
Registered: Not Yet
Location:
Posts: N/A |
quote: Originally posted by toeslider
The line to call me an idiot starts here >
Careful what you wish for! These are touchy physicists - as I found out with my flat-earth joke! Let's let them debate the vectors while we focus on performance.
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03-28-14 04:34PM |
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JB42
Drawmaster
Registered: Nov 2012
Location: Toronto
Posts: 621 |
RockDoc has been anything but touchy. Uncommonly patient would be far closer to the mark.
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04-01-14 02:46PM |
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Flat Hat
Harvey Hacksmasher
Registered: Mar 2014
Location:
Posts: 86 |
I agree about RockDoc, he/thay have been very patient. I finally watched the video from 'smarter every day' on youtube and in the end, I think the conclusion was that neither theory fully explained how rocks curl, and that there may be other forces involved besides the front/back melting and the scratches. in fact one theory was left/right friction impact, which I think bears some further exploration.
Another angle (no pun intended) I've been thinking about is related to how a top spins on the table - perhaps another model we can draw some data from... the top has both precession and will curl in the direction of spin when given momentum. precession may not be the right phenomena to describe my thought - I am thinking the axis of the stone slightly wobbles (imperceptibly) because the force giving the rock its turn is applied off-center of the stone via the back of the handle.
Anyway, there is lots of room for more study here, it's an interesting question.
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04-01-14 03:31PM |
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ChiefIceMinion
Harvey Hacksmasher
Registered: Nov 2012
Location: In the crawlspace
Posts: 83 |
quote: Originally posted by toeslider
- in the case of a vehicle on ice with tires spinning, the tire spinning slowest will have better traction. It is not necessary for the tire to have complete purchase of the surface (or “sticking”’ using terminology from someone’s prior post) to observe that the tire spinning slower has superior traction
There are different effects in play with the spinning tires - I believe the straightforward explanation is that the coefficient of rolling resistance for the slower tire(s) is different (higher?) than the faster tire(s), giving the slower tires more friction (grip) against the ice. However, I'm a chemist, not a physicist, so this might be incorrect.
quote: .
- corner sweeping works. If you sweep only one side of the future path of the running surface you can affect the travel of the rock. If the rock is not spinning excessively, by sweeping the “inside” of the curl you can actually change the direction of rotation. Any driver training instructor will tell you that warmer ice is worse for traction with a vehicle, so, by sweeping we are warming the ice and decreasing the available traction.
I've not seen nor heard of properly thrown rock reversing rotation due to sweeping. I could see a very weak handle having this occur, though, with the "mechanism" being rough pebble grabbing the unswept side (vs. the smooth pebble that is being swept) and causing a change in rotation.
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04-01-14 03:37PM |
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RockDoc
Swing Artist
Registered: Apr 2005
Location:
Posts: 399 |
quote: Originally posted by toeslider
I find it very hard to not find some merit to the “fast side vs. slow side” approach to an answer
But this idea of a difference in friction at the 3 and 9 o'clock positions has been thoroughly discredited since the 1930s. It cannot explain why rocks curl, because the differential forces are applied in the forward/backward direction. Only differential forces near the 12 and 6 o'clock positions can generate the necessary sideward force. Both the Shegelski and Nyberg approaches recognize that limitation, as have many other investigators since nearly the beginning. Alternative explanations of why rocks curl have to look elsewhere than the 3-9 o'clock explanations. And all the generic differential friction models don't look too good, either, because they predict less curl than is observed for real stones, and predict that curl increases with rotation rate, both of which are real defects in the models.
quote: Being that the lateral motion is 3 to 4 feet compared to the 100 to 120 feet of forward motion we are only looking for a very small force, or differential between forces.
Absolutely true. The sideward forces are small compared to the forward force applied at the time of delivery. Toward the end of the travel of the stone, the imparted sideward motion can become a larger fraction of the forward motion, and this creates a sharper angle of deviation from a straight line path than when the stone is traveling faster. Nyberg showed that the scratch-guiding model predicts that the net sideward force generated is relatively independent of rotation rates, so this is possible as the stone slows down in its forward motion.
Not sayin' that Nyberg has explained everything. But the Nyberg model explains more than any previous model, and has been experimentally tested. If there is a better model, it has to beat this one. (And it needs to fulfill basic principles of physics as well as experimental tests.) My students have lots of theories about laws of motion and principles of atomic structure and bonding, but very few of them are correct. (They sound good, mind you, but they don't explain reality.)
There is considerable value in knowing how curling rocks curl at the scientific level. You may not be able to improve performance (except by blind luck or coincidence) until you understand what physical principles must be managed.
Another stodgy area of study comes to mind: cooking. For HUNDREDS of years, it was lore in all the best cooking schools and kitchens in the world, that we sear meat to "seal in the juices," and by doing so, it tastes better. Except some enterprising scientists tested that hoary line a few decades ago by weighing steaks before and after searing, and found that they had in fact LOST mass and moisture. It turns out that we sear steaks not because it seals in moisture, but because of the complex chemical reactions that occur on the surface of the hot pan (the Maillard reaction) that make tasty little brown bits. There are hundreds more of this kind of lore in the field of cooking that is based on misunderstandings of physical observations, and unsupported theories. (Curling and many sports are like this. Look at the resistance to using curling statistics to think about game management--e.g. Curl with Math.) Cooks got it right sometimes by accident. Now that professional chefs know the whole tale, they can more precisely prepare tasty food. (And every professional cook trained today can probably tell you what the Maillard reaction is.)
Cheers.
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