Prop wrote:Dan-cat wrote:Reply to me on PM by Acesinc, on transmitted side:
acesinc wrote:Looks good, Dan, well done!
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Which confirms what I was saying about left spin on the cueball becoming right spin on the object ball, and vice versa?
Hi, Prop. Is this meant to be rhetorical, or a question in search of an answer? I don't mean to stick my nose in where it's not wanted but, yes, in a sense, left spin on the cueball becomes right spin on the object ball. However, conceptually, that is very, very misleading and so not quite exactly true.
Warning!: I suspect this will be a very long, dull post ahead. I expect multiple dancing zebras. Continue...
First, I will preface by saying that if you are interested in this topic of "spin transfer", believe ANYTHING that Dr. Dave says on the subject like it is gospel. My dedication to the topic is limited, my personal research into it is limited, I have read and viewed some of the absolute wealth of info that Dr. Dave has made available to us, but fully admitting my own limitations, Dr. Dave has devoted a good portion of his life collecting and verifying information as to the physics of colliding billiard balls on a flat, baize covered surface. Repeat some of his experiments for yourself and you will believe.
Second, I will say that I have not seen Dr. Dave record any of his experiments on an actual proper snooker table, only American pool tables. The two primary differences (aside from the obvious peach basket sized pockets of an American table) are that 1), the American cloth is unnapped while a proper snooker cloth has a directional nap. Everyone ought to know that already although, as an aside, the first snooker-specific instructional book I read was by Cliff Thorburn and in it, he admitted his ignorance that he was playing the game for TEN YEARS before he even realized the nap of the snooker cloth has a very real effect on the path of the balls that must be accounted for in order to excel at the game. And 2), the cushions of an American table have a pointed profile that is nearer the billiard ball's center of gravity while snooker cushions have a flat face relatively higher to the ball's center of gravity. This results in the snooker cushions "flattening" the rebound while the American style cushion give an angle of reflection that is nearly equal to the angle of incidence. All this means is that, conceptually, the effects of transmitted side between balls is the same, but specifically, how you play any individual stroke will necessarily depend on the table type upon which you are playing.
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Now that those qualifiers are covered, I will give a back story. If you want to skip ahead, go to the next long line.
As an American kid, I grew up playing baseball. A lot. We all dreamed of playing in the Big Leagues and tried to do things in our little baseball world the same way the pros did. A lot like Snooker in that regard. We were kids so we weren't supposed to try to throw curve balls, but we did anyway. It never worked but the concept was simple and obvious.....put enough spin on the ball and its path will change over the course of the flight of the ball. As I grew up and turned more and more to the recreational sport of the billiard games rather than continuing to punish my body with the grueling young man's games, I always thought of curving the cue ball as being essentially similar to "throwing a curve ball" in baseball. (For any reader with no inclination toward baseball, the same physics describes the arcs and curves of a golf ball or a tennis ball.)
It is not all that long ago, less than a decade perhaps, that I actually realized that curving a cue ball on a solid, flat surface is not at all the same as curving a ball in flight through the medium of air. The two things are in fact, very nearly the exact opposite of each other. This will require a little explanation, but the two fundamental differences between curving a billiard ball (henceforth, "snooker ball") and curving one of the other sport balls described (henceforth, I will just say "baseball") are that 1) throwing a baseball, it will initially travel relatively straight and will gradually begin to curve later in its path with the intensity of the curve increasing the further it travels, while curving a snooker ball, it will initially curve the greatest at the start of travel and straighten out as it continues, and 2) viewed from overhead, an anti-clockwise spin on a baseball will result in a curve to the
left as it is viewed from the thrower's perspective, while an anti-clockwise spin on a snooker ball will result in a curve to the
right as viewed from the striker's perspective.
Point 1) above is rather complex physics and aerodynamics and not too relevant to the snooker discussion here except at one very specific point in time at which I will refer back to it. Point 2) is critical and non-intuitive. Put simply (like when I was a kid playing baseball), one would think, "Just spin the ball and it will curve." In reality, that is not exactly true either for a ball flying through the air, nor for a ball spinning/sliding on a flat surface.
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So getting more specifically to the topic of Snooker, why DOES the cue ball curve when we put a spin on it. It is probably not quite what you think. The obvious part of the equation is that it has to do with friction, but there are many different ways to think of friction. Every different type of material has a different property of surface friction. Snooker would play much differently if the surface were a sheet of teflon rather than a woolen baize. But here, I want to differentiate between point contact, line contact, and surface contact. Think of the cue ball like it is a globe....north pole, south pole, and everything in between. The contact "point" of the ball with the cloth as it rests is the "south pole". Imagine that we can stick a very fine needle through the table and into the exact south pole of the cue ball and another needle from the top into the north pole so the ball is trapped. It cannot move except to spin. If we strike in the center of the cue ball with our cue stick, something is gonna break. But if we strike off to the side, say to the "east" of our globe, the tip will strike the edge of the ball and deflect off to the horizon, and the cue ball will now spin about the axis of the two needles in the north and south poles without traveling at all.
Now we go to the other extreme: surface contact. It does not exist as the ball rests on the cloth. To have "surface friction", we would need surface contact of some dimension, such as a CUBE resting on the flat surface. A sphere of course can only have point contact and point friction on the table surface. Cushions are a different story. When a snooker ball strikes a cushion, we do in fact have surface contact because the rubber deforms and conforms to the shape of the ball's round surface. THIS is the reason the Snooker cushions react differently compared to American Pool cushions: greater surface contact equal greater energy absorption and "flattening" of the rebound angle.
That leaves line contact. This is actually the biggie because THIS is what allows the snooker ball to curve on the baize. For visualization, again think of the cue ball as a globe like the needles in the poles thought experiment above. This time, imagine the south pole is NOT the contact point with the surface, but instead, the globe is tilted a little bit so the exact point contacting the baize is on the Antarctic Circle. So imagine what will happen if that Line of Contact, the Antarctic Circle, remains in contact with the baize. The cue ball curves! The cue ball rolls along and a point on the Antarctic Circle is continuously in contact with the cloth so the cue ball would traverse a continuous perfect circle as it sort of rolls along on its tilted axis.
Obviously, this is not exactly what actually happens; it is only meant as a thought experiment in order to help visualize what is going on. But think about this.....what is the most extreme example of curving the White? Obviously, a masse shot. Most have probably seen Jimmy White's famous masse though the stroke is not common in Snooker, much more common in other cue sports. Visualize this stroke.....the cue stick is brought to vertical and the cue ball is struck off center through the "northern hemispere", the idea being to impart an extreme spin and tilt the cue ball off its north/south pole axis in order to make it "roll" along the line of the "Antartic Circle". Makes perfect sense! This where that "not too relevant" point 1) comes into play......with the masse, there is a huge curve of the White at the start of the stroke, then the ball straightens its path as it continues to roll. Again, all of this not exactly perfectly accurate, but this thought experiment makes things much easier to visualize.
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There is still one topic yet to cover before we finally get to the White actually contacting another ball in order to "transfer spin". In general, beginning players are always taught to focus on striking the cue ball on center as a basic fundamental. Everyone probably knows the expression, "unintended side". It is fine to strike above center (follow) or below center (screw), but if you strike the White off center to either the left or right, whether accidentally or with purpose, you run the risk of the White going off the line of aim. Clearly, this is because when you impart side, whether it is intended or intended, the White will nearly certainly curve, as described above. Therefore, you must learn to compensate with your line of aim as Johnny described in a post earlier. But there is another element to this that most players DON'T seem to realize. Yes, you CAN play with side AND make the White travel in a straight line. To do this, there are two steps that you MUST take to use side and strike the White straight. First, DO NOT try to impart too much side, just a trace. Americans have a surprisingly useful measure for this that I have not heard in Snooker circles, and that is "tip diameter". When you play with screw or follow, it is possible to go to the extreme and still control the stroke. You can strike nearly the very tippy top north pole of the cue or you can strike so low for screw that you risk tearing the cloth, but if you have good technique, you can still pull off those shots. This is not the case with side. To control the shot and make White travel straight, NEVER strike more than one cue tip diameter off the vertical centerline of the ball. By definition, "one tip diameter to the right" would mean that the vertical centerline of White would be tangent to the left edge of your cue tip. Go out further than that and good luck to you; I can't help. To be clear, this recommendation is for those cases where you are expecting to pot a ball and play a position. Sometimes, of course, we "hit and hope" such as escaping a snooker or whatever so you may need to use extreme side, but you won't control the stroke very well at all. If you want to make the cue ball travel in a straight line the direction you are aiming, keep the side to one tip diameter or probably less than that. BadSnookerPlayer once said, "Snooker is a game of eggshells" and this is another example that to excel at the game, you must learn to be subtle and delicate. Second thing you MUST do for the White to travel straight when using side is to keep the cue stick PERFECTLY level when striking. Okay, I have to admit........this is actually impossible to do. Think about it; the butt of the cue is what? about 30 mm? So if the butt of the cue is touching the cloth perfectly level the center of the tip is 15 mm above the cloth. So to strike perfect center of the cue ball, you can only raise the cue 10 mm above the cloth. You can't even wrap your fingers around the butt, you have to hold it in your fingertips on the sides. Suffice to say that in normal circumstances, you CANNOT hold the cue PERFECTLY level. But this is to make the point that when you elevate the butt of the cue even slightly, say 6 or 8 inches above the table surface, then you are necessarily imparting a downward force even if playing above the equator of the ball (think of that extreme masse shot) so by the laws of physics, the cue ball WILL curve off line and there is nothing you can do to stop it. The very important consequence of this that you must understand is that in order to have a chance of hitting the White STRAIGHT when using even a trace amount of side is that the butt of your cue must be clear of interference and you must keep it as low as possible. If you want to play a stroke with some side, but by necessity you must elevate the butt of the cue 4 inches, 10 inches, 2 feet (as in playing over an interfering ball), then compensate your aim because the path of the White ball WILL curve, simple as that.
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FINALLY! We can allow our White ball to actually strike another ball and transfer some side!
As I said very early on, to phrase it this way is definitely misleading. I think a better phrase might be to "transfer some turn". As I am wont to do, I will attempt to explain.
The general argument against the possibility of side being transferred from White to object ball is, "What do you think these are, cogwheels? The first one rotates left, the second rotates right, the third left again and down the line?" Ummmm........no.
As Dr. Dave explains properly and thoroughly, some small amounts of spin WILL be imparted to an object ball in most circumstances whether a stroke was played with side on the White or not. The only exceptions would be 1) when the object is played full ball with no side, intended or not, on the White, or 2) if a lubricating substance is used on the contact point between the balls to render friction negligible. So the point is that nearly every stroke played on a snooker table actually involves some amount of side being transferred to the object ball. How do we deal with that? Especially if we didn't even know it? Simple, it is just instinct and experience. You have been playing the game a long time, you see how things work, your brain just compensates for things based on subconscious knowledge you have picked up in the past. But if you can start to understand these things, you will probably start to improve faster.
"Wait! What?! Whoa!! Back up.....beep, beep, beep! Side is transferred on nearly every stroke?
?????????
Yes. Not a lot. Just a little bit. So little is transferred that chances are, that tiny amount of transferred side will not likely have any effect at all as to whether a ball pots or not. We don't even notice the tiny amount of side transfer normally. We only notice it when we maximize the circumstances to make it happen. Such as helping side, or changing the trajectory of a ball off a cushion.
Let's take an example, an extremely fine cut. In fact, nearly the finest cut possible. Connect the lines of centers of the White to its "ghost ball" and the line of centers of the object ball to a center pocket. Say those lines form a 91 degree angle and you can strike White perfectly straight as strong as you need to for object to reach pocket. What will happen?
To visualize this, it is easier to think of the balls not as spheres, but believe it or not, think of them as cubes. The cubic "White" is lined up with a face parallel to the side cushion. The cubic "object" is turned 45 degrees......like it is a "diamond" to the white's "square" when viewed from overhead. So the "White" is struck perfect center ball to pot and contacts the object at its very tippy, tippy "point" to send it toward its pocket. Will that "diamond" just slide over into the pocket? With this visualization, you can easily see the diamond will in fact start rotating due to the glancing blow it received at contact. Since the object is now indeed spinning, it is going to turn just slightly off its intended line. It needed to pot at a 91 degree angle, but in fact, maybe it goes off at a 92 degree angle instead. Does it still pot? Of course; if it had been a sphere (and indeed, it is,) we never even would have noticed the imparted side.
Feel free to argue this if you want, but Dr. Dave has the high speed video to back it up.
So transferred side is happening all the time, we usually don't notice. But when we are aware of it, we can use it to our advantage.
As for the actual amount of transfer, it is tiny, even in the best of circumstances. An edge of a cube struck by another cube (line contact) is going to start spinning A LOT more than the edge of a sphere struck by another sphere (point contact). Nevertheless, the effect is there.
I think people think of the snooker balls as if they are spinning tops, whirling around at high speeds. So if we fools claims that "side is transferred", then that must mean that the White whirling around at a high speed strikes an object which we are claiming must also begin whirling around at a high speed as if they are so many cogwheels.
Again, ummmm........no.
"Spin rate" is generally measured as "RPM's" (revolutions per minute. Or rotations per minute if you prefer.) There is a big problem with thinking of it this way when talking about snooker balls. Have you ever seen a snooker ball spin on the baize for a full minute? And even less likely than that, have you seen it spinning for the full minute without even slowing down due to the surface friction with the table? Obviously not. Snooker balls, when we can even detect that they are spinning at all, will only spin for a second or a few seconds at most and will be in a continuous state of deterioration of the RPM's the whole time. (I am going to invent some numbers here just to illustrate and make the maths easy; full disclosure, I have no idea about the actual spin rates. Dr. Dave probably has that information somewhere.)
So let's say a cue ball is struck with an initial spin rate of 600 RPM. I guarantee it will not continue rotating for a full minute. So it won't get anywhere near 600 actual rotations. Say it continues rotating for six seconds before stopping (probably won't, but another thought experiment, we will just say that). So that is 1/10th of a minute so it must have rotated about its axis......ummm........60 times in total. No, still not even close. During that entire 60 seconds, rotation was continuously slowing down due to friction until it eventually stopped completely. So how many actual rotations did the cue ball make? I have no idea, and I am not interested enough to figure it out (because it won't improve my snooker skills), but maybe it will complete, say, one-half that amount, 30 rotations. TOTAL.
Now let's say that White ball struck an object very early on so that some spin was imparted to the object ball by contact. What would be the INITIAL rate of spin of the object ball? Again, I have no idea. But let's just pluck another magic number out of the air and say that 1 percent of the initial 600 RPM will transfer. (We always knew it wasn't much; one percent isn't much.) That means the object's initial spin rate will be 1 percent of 600 or 6 RPM. Remember the "M" means "minute". So the object WOULD rotate a meager six times if it could continue to rotate a full minute. Which it won't of course. So it is a tiny amount of transfer. But it is enough that we can use it for certain things like Dan's shot.
Yes, the balls do act like cogwheels......White right spin, first object left spin, second object right spin again, etc. .........but with an absolutely massive loss of momentum in between contacts. You would need precision instruments to detect spin transfer beyond that first contact but it is still there.
And that is why I suggested "turn transfer" rather than spin transfer. I doubt that object ball even makes a single revolution on its north/south pole axis. It doesn't really "rotate" at all; simply tilts a little on its axis then starts its journey off at just a little different angle than it would have if "friction" didn't exist. Think of it more like this.....the cheetah is chasing the gazelle on the African savannah. The cheetah needs to make a turn so it sticks out its tail to counter-balance, digs a claw into the ground, and turns off at a different angle. Same sort of thing happens with the transfer of spin. The White ball contacts and the light transfer of friction through point contact digs into the object ball knocking it off-kilter a bit, and the "claw" of the object ball's point contact digs in and sends it off at a slightly different angle like the cheetah. All this is a fraction-of-a-turn of the object ball.
To be clear, all of this must occur over a very short time and a very short distance, otherwise, all of the turn momentum will be lost to friction. So for instance, Dan's stroke to pocket the black ball was firm; White still had plenty of spin to transfer when it reached black ball, black reached cushion quickly so it still maintained a tiny bit of the "turn" that it picked up when it actually contacted cushion. If you stroke lightly and your object must travel the full width of a snooker table, no way that it will retain any of the turn by the time it gets there. Remember........when curving a snooker ball (unlike a baseball, golf ball, or tennis ball), the curve would be stronger at the start and straighten out over time and distance.
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Please do not quote this post! Just replace it all with dots. No need to put everyone through that torture again.
Commence the dancing zebras!