Center of Percussion ( for Bob Jewett)

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daveb

AzB Silver Member
Silver Member
I recently read Mike Shamos' article in Billiards Digest about the "center of percussion" on the cueball and it's importance to rail height. A number of years ago, a VERY well known pool instructor advised me to hit the cueball about a half tip above center on the vertical axis when kicking at balls to get a more consistent angle of incidence to angle of reflection and thus greater kicking accuracy. After reading the Shamos article, I realized that I was being told to hit the cueball at a point corresponding roughly to this "center of percussion" or aproximately 63.5 percent of the height of the cueball.. The article pointed out the importance of this in minimizing any unwanted overspin or underspin induced by the rail.

My question is simply this, do you think that contacting the cueball at the center of percussion on the vertical axis can provide greater kicking accuracy, given all the other standard considerations (ball speed, tip placement,dirt, cloth, humidity,etc., etc., ad nauseum) ??
 
I am no science expert...but I have a hunch that this ties into the "can't get overspin on the CB"

I don't think you want a ton of follow on the CB when kicking off a rail (unless your intent is to change the "out" angle)...but at the same time a center ball hit will produce a sliding ball that potentially is still sliding when it contacts the rail....add to that...now you have a variable of "how much is it sliding at impact of the rail?" It could vary slightly from stroke to stroke which (I suppose) could cause variables in the "out" angle....I suspect a (smooth) naturally rolling CB would be more consitent on the "out" angle.

I think the whole key (no matter how you do it) is to have a smooth naturally rolling CB when it contacts a rail.
 
My opinion is that much like a golfer , for max consistancy , you would want to get the cb/golf ball into a 'roll' (no skid or spin) as soon and as smoothly as possible. Consistancy usually = accuracy.

Striking it as you suggest should do that and help minimize unwanted deviation.
 
daveb said:
I recently read Mike Shamos' article in Billiards Digest about the "center of percussion" on the cueball and it's importance to rail height. A number of years ago, a VERY well known pool instructor advised me to hit the cueball about a half tip above center on the vertical axis when kicking at balls to get a more consistent angle of incidence to angle of reflection and thus greater kicking accuracy. After reading the Shamos article, I realized that I was being told to hit the cueball at a point corresponding roughly to this "center of percussion" or aproximately 63.5 percent of the height of the cueball.. The article pointed out the importance of this in minimizing any unwanted overspin or underspin induced by the rail.

My question is simply this, do you think that contacting the cueball at the center of percussion on the vertical axis can provide greater kicking accuracy, given all the other standard considerations (ball speed, tip placement,dirt, cloth, humidity,etc., etc., ad nauseum) ??
Click to expand...
I believe so it sounds true anyshot is more accurate with the hit you described and right going right and left going left off the rail accurate natural angle. In my opinion.:cool:
 
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daveb said:
I recently read Mike Shamos' article in Billiards Digest about the "center of percussion" on the cueball and it's importance to rail height. A number of years ago, a VERY well known pool instructor advised me to hit the cueball about a half tip above center on the vertical axis when kicking at balls to get a more consistent angle of incidence to angle of reflection and thus greater kicking accuracy. After reading the Shamos article, I realized that I was being told to hit the cueball at a point corresponding roughly to this "center of percussion" or aproximately 63.5 percent of the height of the cueball.. The article pointed out the importance of this in minimizing any unwanted overspin or underspin induced by the rail.

My question is simply this, do you think that contacting the cueball at the center of percussion on the vertical axis can provide greater kicking accuracy, given all the other standard considerations (ball speed, tip placement,dirt, cloth, humidity,etc., etc., ad nauseum) ??
Click to expand...
For consistent kicking, you want the spin on the cue ball when it gets to the rail to be consistent. Once stated, I think this is obvious, but it needs to be stated.

The natural state of the cue ball is smooth rolling on the cloth. If you have any distance to the cushion, and don't shoot too hard, the cue ball will be rolling smoothly on the cloth when it gets to the rail. The simple argument is that you should start the cue ball with smooth rolling so that it will always have smooth rolling and you aren't guessing about how much "hook" you're going to get after hitting the rail. The required height of tip contact on the cue ball is 70% of the ball's height to start with smooth rolling.

The more complex argument is that you may want to bring the tip down a little on the cue ball if you have a long distance to the cushion and aren't shooting hard. This makes your speed more uniform, and the cue ball will be rolling smoothly anyway by the time it gets the cushion.

A still more complex suggestion comes from Ron Shepard: on kicks, get the cue ball to arrive at the cushion without follow or draw and just enough side spin to make the angle of incidence equal the angle of reflection. There are excellent reasons to do things this way if you can. Mostly, it makes one-cushion kicks much less dependent on the table.
 
BRKNRUN said:
I think the whole key (no matter how you do it) is to have a smooth naturally rolling CB when it contacts a rail.
Click to expand...
I believe this is correct.

The center of percussion for the CB is 0.4R, where R is the radius of the CB, above center. Striking the CB at that point would cause the CB to achieve natural roll immediately after contact. That way, you're guaranteed the CB will hit the rail with natural roll no matter how close the CB is to the rail.

The question then becomes why do you want the CB to achieve natural roll when striking the rail? If the CB is stunned into the rail (sliding, no roll), then the outcoming angle will always be somewhat less than the incoming angle, due to friction between the rail and the CB, and also because the rail isn't perfectly elasticity. If the CB is rolling into the rail, then the forward roll naturally widens the angle coming out. It will turn out that the resulting outcoming angle will closely match the incoming angle.
 
Based on the OPs question of accuracy , I think you'd want absolute consistancy. I don't think it matters as much about in and out angles being perfectly matched as much as if you know exactly what they are going to be (with in reason) each and everytime. As you become a better player , you are better at estimating the other variables (spin/speed/etc) and use them to your advantage but just as with the use of english , removing the variables will always add constitancy to the core. Then you can build from that.
 
daveb said:
I recently read Mike Shamos' article in Billiards Digest about the "center of percussion" on the cueball and it's importance to rail height. A number of years ago, a VERY well known pool instructor advised me to hit the cueball about a half tip above center on the vertical axis when kicking at balls to get a more consistent angle of incidence to angle of reflection and thus greater kicking accuracy. After reading the Shamos article, I realized that I was being told to hit the cueball at a point corresponding roughly to this "center of percussion" or aproximately 63.5 percent of the height of the cueball.. The article pointed out the importance of this in minimizing any unwanted overspin or underspin induced by the rail.

My question is simply this, do you think that contacting the cueball at the center of percussion on the vertical axis can provide greater kicking accuracy, given all the other standard considerations (ball speed, tip placement,dirt, cloth, humidity,etc., etc., ad nauseum) ??
Click to expand...

YES. I found by trial and error, that using a hair of top of center will give you the most accurate kicking angles. Some people will use helping english on kicks.....If you are kicking to the right, then top/right of center (helping english). I tend to only use above center on kicks, unless I have to shorten or widen the angle due to obstructing balls which is done by adding side english. I have found that using low of center will shorten the angle. I don't know why it is this way, or how to explain it. I just know that this is what I have experienced.
 
jsp said:
... If the CB is rolling into the rail, then the forward roll naturally widens the angle coming out. It will turn out that the resulting outcoming angle will closely match the incoming angle.
Click to expand...

I thought that the spin caused the ball to curve after it hits the rail, the 'topspin' takes it wider while a bunch o' bottom brings it back straighter, but again after the rebound.

I play a series of kicks for kicks : Put the cue ball in the jaws of a corner pocket. Shoot at the 3rd diamond on the opposite long rail (1 diamond from the side pocket). Shoot this hard with full top for a roling ball, it will curve into the opposite corner. Shoot this same path with full bottom and the ball will curve to a 'shorter' angle and go two rails into the opposite corner from the starting corner. If you play it with the 'correct' amount of roll it will hit the 6th diamond on the same long rail as the staring position.

Dave
 
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