# The Lonnnngggest Snooker Debate Ever!

Hi guys, I've been having this debate with various snooker players for christ knows how long, and with no physisists amoungst us, the problem's never been resolved.. Please Help!

If check side (hitting the right hand side of the ball onto the right hand side cussion) is used when striking the cue ball, the cue ball returns from the cussion at a small angle than if hitting the centre. This means the ball could return at 90 degrees to the cussion when initially hitting the ball at an angle.

So, given the situation below, where ball A is snookered from hitting ball B:

B
I O I
I I
I O I
I I
I O I
A X

Would check side allow more of the cussion (X) to be hit than if striking the centre of ball A or the left hand side of ball A.

I would've like to create a computer simulation of this, however finding the mathematics behind spin and friction proved a tricky problem.

Also I might add, is there an angle at which side spin no longer takes significant effect due to the lack of horizontal force and increase of forward motion against the cussion.

If anyone has any opinions they really will be greatly appreciated as we've all driven each other mad it seems every time we go for a game of snooker!

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oh dear, that diagram didn't quite go according to plan.. maybe this one will be slightly better:

IBI
IOI
II
IOI
II
IOI
IAI
X

Last edited:
Gokul43201
Staff Emeritus
Gold Member
I thought the cushion was the entire boundary/wall of the table. Why is it designated by an X in the picture?

Note: You can "draw" pictures by using [code ] and [/code ] tags, like for instance :

Code:
 |  B                 |
|  O                 |
...or you can make a picture using something like Paint and attach it directly or upload it to an image host and hotlink it.

Hi, thanks for that. Hopefully it will work slightly better this time. The X simply showed the cushion the cue ball (A) was going to hit before hitting the target ball B (it would seem side would have a lesser effect if it was hit again the opposite cushion)

Code:
_____________________________
|   B                       |
|   O                       |
|                           |
|   O                       |
|                           |
|   O                       |
|   A                       |
|                           |
|                           |
.
.
.
|                           |
|___________________________|
X
I'll try to get a better picture drawn tomorrow and put up on the web.

Cheers.

Last edited:
Danger
Gold Member
Hi, js;
Side-spin will definitely increase or decrease the angle of incidence, and so will the impact force. If done properly, you can also get a masse effect that will bring you off of the rail at a different contact point. I'll wait for your next picture.

rcgldr
Homework Helper
It's not clear to me if you're trying to use the cushion to the side between A and B, or if you're trying to use the cushion near the corner (a two cushion shot?)

Would side spin allow more of the cushion to be hit
What do you mean by hitting "more" of the cushion? The shot can be made with a range of initial angles and side spin on the cue ball. The difference will be the reaction when the cue-ball hits the object ball.

Some pool physics. When striking a cushion at medium or high speed with no side spin, the reflected angle is less than the initial angle. The ball comes off the cushion more perpendicular to the cushion. The harder the impact with the cushion, the more perpendicular to the cushion the ball will bounce off the cushion. At very slow speeds, or at very shallow angles (near parallel to cushion), the reflected angle is reasonably close to the impact angle.

Here's an example video of high speed reducing bank angle:

http://www.engr.colostate.edu/~dga/pool/normal_videos/NV6-6.htm

Variations on frozen bank shots:

http://www.engr.colostate.edu/~dga/pool/normal_videos/new/NVA-2.htm

http://www.engr.colostate.edu/~dga/pool/normal_videos/new/NVA-9.htm

More videos here:

http://www.engr.colostate.edu/~dga/pool/high_speed_videos/index.html

One bank shot I haven't found a video of is this one. Cue ball is A, object ball is B frozen on the rail, and the goal is to pocket B into corner X. The trick here is that A will bounce off B as B bounces off the cushion, getting out of the way of B's path to X. It's a similar effect as the first bank shot video, but without the cue ball being frozen against the object ball as well. Similar to the first bank shot video, a bit of right english with medium speed is used on A to make this shot. If I remember correctly, you don't want to use backspin on A, in the video top spin is used, but partially because the cue stick needs to come quickly off the cue ball for the shot to be legal.

Code:
x_____________________________
| A                         |
|                          B|
|                           |
|                           |
|                           |
|                           |
|                           |
|                           |
|                           |
|                           |
|___________________________|

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rcgldr
Homework Helper
Shortest distance is h in the diagram.

Using left english, shown as i the diagram, results in a path where more of the striking surface of object balls are exposed and not blocked by adjacent balls.

what makes you say h and not g? the dotted balls to the left and right of the object ball are only there to display where the white would end up.

If the white returns from the cushion at a greater angle then judging this would be much harder than center ball, and in particular left hand side (see second diagram)

rcgldr
Homework Helper
jshailes said:
shortest distance is h
what makes you say h and not g?
Imagine a mirror at the cushion. The center path of h would appear to be a straight line, all the other paths would be two angled lines, and the shortest distance is the straight line.

The dotted balls to the left and right of the object ball are only there to display where the white would end up.
If nothing is blocking the path to the object ball, then it makes no difference which one you choose if all you want to do is hit the ball.

If the white returns from the cushion at a greater angle then judging this would be much harder than center ball, and in particular left hand side (see second diagram)
Judging what? What is the goal here? Assuming that you want to pocket the object ball, then usually h would be the best, which would involve a little bit of right spin to get the cue ball to truly reflect off the cushion. If the object ball needs to be struck on it's right side, then i might be better. If the object ball needs to be struck on it's left side, then g might be better.

DaveC426913
Gold Member
I see.

jshailes does not care about the length of the total path of the cue ball nor does he care about whether the total path is straight.

He cares about the spread angle. <-g-> <-h-> and <-i-> are measuring the area of impact along the rail. He wants to know which shot provides the widest window, and thus the highest likelihood of hitting the target.

see attached diagram

Last edited:
DaveC426913
Gold Member
IMO, the point is moot. Applying "english" (what we call it when you apply spin) to a cueball creates a much larger chance for error than any other shot. The straight shot w/ no English is the best shot.

However, that is not what the OP is asking. The OP is asking about which angle is the best (assuming english is not an error factor). Yet in this case, the straight shot is still the best.

Simply put, the window is the widest with the straight shot. Any deviation to the left or right will narrow the window, asymptotically approaching zero. This becomes quite apparent as you exaggerate the angles.

see attached diagram

Last edited:
rcgldr
Homework Helper
DaveC426913 said:
jshailes does not care about the length of the total path of the cue ball.
... but the length of the path affects the required accuracy of the initial strike of the cue ball, so it is a factor.

IMO, the point is moot. Applying "english" (what we call it when you apply spin) to a cueball creates a much larger chance for error than any other shot.
Experienced pool players are used to applying spin on the ball, and it doesn't affect their accuracy. English on a bank shot is more difficult, something not practiced as much unless you play billards. With no side spin, the harder you hit the cushion, the more perpendicular the cue ball will come off the rail. A bit of right english on the cue ball so it reflects off the bank will increase the speed tolerance.

DaveC426913
Gold Member
Jeff Reid said:
... but the length of the path affects the required accuracy of the initial strike of the cue ball, so it is a factor.
Theoretically, sure, but if you roughly calculate the diff, it's negligible.

A rail-to-rail shot going 2 feet downtable, on a 9' reg table will be about 114". Changing the angle of the shot can add about 3" at best to this. The diff in apparent width of a ball at 114" and one at 117" is about 1/50th of a degree, giving you an extra 1/64th of an inch window on that rail. I'm saying that's negligible in practice.

Besides, it's till moot since, as stated, the straightest path is the one that's shortest. Changing the angle adds to the path length, making the angle smaller.

Last edited:
rcgldr
Homework Helper
DaveC426913 said:
on a 9' reg table
It's snooker, regulation table is 6' x 12'. Snooker ball size is a bit smaller, 2 1/16" inch in diameter versus a billard ball at 2 1/4" inch in diameter, and the table pockets are narrower. Your point is correct, the distance increase wouldn't be much. As mentioned, I'd use a bit of right english to allow for more speed tolerance off the cushion, but the path would look like the middle of h, a reflective angle.

Last edited:
DaveC426913
Gold Member
Jeff Reid said:
It's snooker, regulation table is 6' x 12'. Snooker ball size is a bit smaller, 2 1/16" inch in diameter
Yeah, I just picked some reasonable numbers, the calcs are all rough.