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Straightening up

Postby Badsnookerplayer

Rarely a good shot to play but, when I play a double into the middle (particularly at a fine angle) and miss it, sometimes there is hope that it may go in the other side on the next bounce ( a treble). However, almost without fail it will not and the object ball straightens up to be more parallel with the top cushion. I cannot understand this effect as it cannot be due to side. I may be wrong but it seems more pronounced when the shot is played with force.

Re: Straightening up

Postby acesinc

I think this is a completely normal effect; has occurred on every snooker table I have ever played on. If you are not actually playing a double and instead just bang an object ball cross cushions with power, on about the fourth or fifth rebound, it will effectively be parallel to top cushion just bouncing back and forth between two points henceforth. (If you were to just strike cue ball, you probably would not see the same effect because chances are, there will be spin applied to the white, intended or no, and of course, that would affect the rebounds.)

As to why this occurs, I can only speculate but I believe I have a fair idea. First off, the effect is far less pronounced on American style pool tables. The old adage about calculating a double is that the angle of incidence is allegedly equal to the angle of reflection. This is much closer to being true on an American table than an English table. I actually learned a lot about this when I originally attempted to set up my table 25 years ago. It is a Brunswick-Balke-Collender made in the USA back in the 1920's. I had cut my teeth on Rileys when I lived in England. Well, I came to find out that the rubber of the cushions actually has a different shape beneath the cloth. American design is sort of like an upside down triangle and English design is like an upside down letter "L" which basically means American cushions come to a point and English cushions have a prominent flat face. Add to that American design Snooker balls are 2-1/8" diameter, larger than English standard 2-1/16". Long story short.......I had no idea about these things when I purchased the old used table; Snooker is not exactly a thriving market over here with very little available especially when you are on a budget so you takes what you can gets. I explained to my Canadian table fitter that I was looking forward to the table playing just like what I was used to back in England. He said, "You're crazy. This is a Brunswick..." and explained all these things. So I guess a combination of me looking pathetically sad and him being a ridiculously nice guy meant that in the end, he brought my rails back home to his machine shop in Toronto and he re-worked them to accept the "proper" rubber and ball size, so in all likelihood, I am currently in possession of the only Brunswick-Balke-Collender snooker table that plays to exact English standards.

That was all an aside eventually leading to my theory of your query. In my ongoing study of the game, one of the tidbits I came across is that the contact point of the cushion to the ball is theoretically at a height of 0.62 times the diameter of the ball....think of it like the ball is a globe: the point at which the ball will contact cushion is well above the equator. Add to that the fact that on English snooker cushions, the flat face of the cushion means there is a lot more material above that contact point......as the "globe" sinks into the cushion, a lot more energy is being absorbed in the "northern hemisphere" and there is no material at all in the "southern hemisphere", just open space. You might think, "Why doesn't it rebound off the cushion at the equator?" Historically, when the rails were added to billiards table hundreds of years ago, their sole purpose was to keep the balls from falling off the edge of the table. And of course, they serve the same purpose today and more. If the rebound contact point is too near the equator, the balls would have a tendency to jump up and off the table A LOT. Remember that video with all of the spins applied and balls bouncing around? Snooker is quite a three dimensional game so the shape of the cushions are designed to retain the balls and direct the rebound back to the bed of the table if bouncing.

So the upshot is that all the extra rubber material in the "northern hemisphere" tends to absorb that energy so that the angle of incidence does NOT equal the angle of reflection. With the American pointed design, there is less material above the equator so the rebound is more accurately reflected. For exactly the same reason, it is tougher to play at the White from tight on cushion on the English table.

Re: Straightening up

Postby Badsnookerplayer

Thanks Ace for the detailed response. I had not considered this before but need to give it some thought before I totally understand it.

Re: Straightening up

Postby Badsnookerplayer

Tested this again today. The straightening up of a treble (or more bounces) is much more pronounced when the shot is hard. If you play soft, then there is no noticeable straightening up effect. I think it therefore occurs because the deformation of the cushion is not symmetrical as it is deformed more on the ‘far side’ of the shot.

Re: Straightening up

Postby acesinc

rekoons wrote:So this is the opposite of the slide effect on more oblique angles then?

https://www.youtube.com/watch?v=J-NZHx- ... e=youtu.be


I suppose that is a way that you can think about it if it helps you to judge your stroke correctly. In my mind though, I see the two effects as having two completely different and (in my opinion) unrelated causes. First off, I will say that (again, in my opinion,) anything that Barry Stark says, believe it. Incredibly intelligent snooker guy and I think his presentation is excellent to make the point clear. Coaching is about communication....a coach may know everything there is to know about a subject but if he cannot effectively communicate that knowledge to a student, then he is not a very good coach. Just because someone is a very good snooker player does not necessarily mean that person will be a good snooker coach. Barry Stark is a fantastic coach, the whole package.

But more to your point, what I was trying to say early on about "straightening up", I believe it occurs because a firm strike of a ball INTO the cushion causes the rubber to compress, and then of course it de-compresses, pushing the ball away from it like it is a trampoline. However, the ball will reflect at a straighter angle because the rubber absorbs a lot of energy into it before pushing the ball away. This is where language fails me...I am having a hard time communicating this concept properly. I think BadSnookerPlayer hit this nail on the head when he described it as, "I think it therefore occurs because the deformation of the cushion is not symmetrical as it is deformed more on the ‘far side’ of the shot."

But the "sliding" is an easy concept for me to explain. Similar to "squeeze", "slide" is just a term that we use, a word to connect the idea with the reality of what actually happens in the physical world. (By this, I mean we use the term "squeeze" but nothing is actually getting squeezed at all and we use the term "slide" but nothing is actually sliding at all......these are simply words that we use so that others know what effect we are talking about when we say these words.) So what is it then that is actually happening when the cue ball is "sliding" off the rail? Easy to understand....

First, imagine setting up White on Green spot, Brown and Brown spot and simply strike Brown along the Baulk line straight into the cushion. Of course, it rebounds straight back at you. Now, same thing but take Brown away and strike White directly into the cushion. You can do one of three things: centerball strike White rebounds straight back at you, left side on White and it reflects toward Blue spot, right side on White it reflects toward Baulk cushion. So spins have an effect on how a ball comes off cushion. That is obvious. But what is NOT obvious is that the cushion will INDUCE spin onto a ball simply by the friction between the two surfaces.

Now, let's apply that knowledge you probably already had to this concept of "slide"....a similar scenario to Barry Stark's but a slight change. Black on Black spot and place White on a theoretical spot which is the exact mirror image of the Black spot on the Baulk end of the table and we are going to strike side cushion on Yellow spot side. Again, with the "equal angles" theory, you would need to hit the White to the space that is occupied by the middle pocket in order to hit Black. But you know that is not true. If you hit a spot on cush a few inches to Baulk side of middle pocket, White will "slide" off the cushion and strike the Black on spot. What happens is easy to understand....you strike White centerball, but when White strikes a GLANCING BLOW on the cushion, the cloth of the cushion has a gripping effect on the surface of the cue ball because of simple friction (very much like a well chalked tip has a gripping effect on the cue ball), so this gripping effect will INDUCE spin on the White. Might be easiest to think of it this way.....White WANTS to travel in a perfectly straight line. But the cushion gets in the way. ONLY think of the right hand edge and the left hand edge of the cue ball (again, assume like Barry Stark's video we are hitting the cushion on the Yellow ball side). When White contacts cushion, the RIGHT edge of the cue ball slows down dramatically through contact with cushion while the LEFT edge of the cue ball wants to continue travel in a straight line. This then describes exactly HOW the spin is imparted by the cushion. It is exactly the same as if you yourself applied the left spin with your cue tip. So as the White rebounds off the cushion, it "slides" off at a more shallow angle exactly like when you struck White along the Baulk line with left had side applied. Simple.

The more shallow the angle, the more glancing the blow, the more spin will be imparted onto the White by the cushion. This is strictly a matter of experience and judgement by the player. The truth is, very, very few players probably understand the physics of what is happening as I explained it above. Instead, it is just a matter of experience, and trusting the gut instinct, and learning over time, and simply referring to the idea as "slide".

If you actually understand what is happening and why, I believe you will dramatically shorten your learning curve and you will begin to play these types of shot much more accurately immediately. Good luck!

Re: Straightening up

Postby acesinc

Oh, and by the way, Rekoons, here is another related but not obviously related version of the "slide" effect. Have you ever noticed how, if you are trying to pot a ball at an angle that is maybe two feet away from the corner pocket and it is actually physically touching the cushion, it seems like it is much easier for some reason than potting the same ball just a small distance off the cushion, say a quarter inch or so?

This is due to the same "slide" effect. In either case, it is critical to strike at a very accurate potting angle but you have just a little larger margin for error when the object ball is touching the cushion. This is because when that ball starts to move after contact with White it immediately has the "slide" effect on it....it is hugging that cushion because that side of the cue ball is continuously in contact with the cushion so that side is constantly in a state of deceleration while the free side away from the cushion is constantly trying to travel in a straight line. So it seems to stick to that cushion like glue. Makes sense. But when the object ball starts out even slightly away from cushion, you will nearly always get that "glancing blow" and it will then bounce away and not pot.

You probably already knew that touching cushion seems easier to pot but you never really knew why.