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View Full Version : Need help with tangent lines...

Billy_Bob
01-10-2005, 11:32 AM
Playing 8-ball... I want to shoot the 1 ball into the corner pocket as shown below. But I want to know where the cue ball will hit the 8 ball after this shot and where the 8 ball will go.

Am I correct that the cue ball will travel along the green line and not the red line? (Cue ball travel path is actually 1 1/8 inches out from 1 ball?)

So in this case, this shot will make the 1 in the corner and the 8 in the side?

Would draw or follow change where the 8 would go?

(I am making the mistake of thinking the cue ball will travel along the red line and would make the 8 ball head toward the far center diamond...)

http://endeavor.med.nyu.edu/~wei/pool/

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DavidMorris
01-10-2005, 11:59 AM
Both. /ccboard/images/graemlins/smile.gif Assuming a stun shot, i.e. the CB is not rolling forward or backward upon contact (which is what you'd get at this short distance with a centerball hit unless you tap it), the center of the CB will take the green path, and the edge would be on the red path. In the specific shot you diagrammed, it would take a pretty firm hit to pocket the 8B, though, because the cut angle on the 1B is so slight. The fuller you hit the first ball, the less energy remains on the CB to move along the tangent line and do much else.

Follow and draw make a load of different in the tangent line rule. The tangent line rule only applies to a stop/stun shot. Follow makes the CB bend forward of the tangent line (away from you) and draw makes it bend back toward you. ALL shots will initially depart from the contact point on the tangent line, regardless of spin, then the spin will take over and bend the path. The harder the shot, the more distance it takes to bend away from the tangent line. Sidespin (english) has no practical effect on the tangent line.

SpiderMan
01-10-2005, 12:41 PM
<blockquote><font class="small">Quote Billy_Bob:</font><hr> Playing 8-ball... I want to shoot the 1 ball into the corner pocket as shown below. But I want to know where the cue ball will hit the 8 ball after this shot and where the 8 ball will go.

Am I correct that the cue ball will travel along the green line and not the red line? (Cue ball travel path is actually 1 1/8 inches out from 1 ball?)

So in this case, this shot will make the 1 in the corner and the 8 in the side?

Would draw or follow change where the 8 would go?

(I am making the mistake of thinking the cue ball will travel along the red line and would make the 8 ball head toward the far center diamond...)

http://endeavor.med.nyu.edu/~wei/pool/

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<hr /></blockquote>

Billy,

It's hard to estimate perfectly because of the small size of the diagram, but it looks like you are correctly assuming the eight toward the side. This further assumes that the cueball is sliding (no topspin or backspin) upon contact with the one.

You could alter the results using topspin or backspin, but remember that the cueball's path away from the one will initially be the same (90 degrees) until the spin takes hold. The harder you hit, the greater the distance of 90-degree travel before the spin grabs.

What this means is that it would be very difficult to drive the 8-ball to the far center diamond because you'd have to hit it hard enough to get it there, and the topspin wouldn't create much bend before the cue contacted the eight.

If you really wanted to drive the 8-ball to the head rail, you could add some right english. This would allow you to cut the 1-ball thinner but still throw it in. The cueball would then hit the eight a little more on the right, driving it a little more to the left, plus the spin-induced throw of this thick collision would move the eight further to the left. It would all depend on the initial placement of the balls, in more detail than can be illustrated on the Wei table.

SpiderMan

Wally_in_Cincy
01-10-2005, 12:44 PM
<blockquote><font class="small">Quote Billy_Bob:</font><hr> ...Would draw or follow change where the 8 would go?.. <hr /></blockquote>

I think you could put draw on the ball and end up at "A" and shoot the 8 in the same pocket

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DennyS
01-10-2005, 12:45 PM
Billy here is an example. It's not exactly how you had it. It's something I had in my files. David had a pretty good description of how and why.
http://img.photobucket.com/albums/v201/DStewart1/billybobexample.jpg

randyg
01-11-2005, 06:36 AM
Dennis: Keep up the great work. These posts help even an old dog like myself....SPF-randyg

DennyS
01-11-2005, 07:15 AM
Thank You Randy! DennyS

Bob_Jewett
01-11-2005, 02:38 PM
<blockquote><font class="small">Quote DavidMorris:</font><hr>... ALL shots will initially depart from the contact point on the tangent line, regardless of spin, then the spin will take over and bend the path. The harder the shot, the more distance it takes to bend away from the tangent line. ...<hr /></blockquote>
A small nit to pick here.... The curve starts as soon as the cue ball leaves the object ball, but at higher speed, the curve is broader and may seem to have an initial straight section. The shape of the curve is a parabola until the cue ball goes into smooth rolling on the cloth.

DavidMorris
01-11-2005, 03:18 PM
Well, I certainly don't mind having my nits picked by someone like you, Bob. /ccboard/images/graemlins/wink.gif

Hmmm, somehow that sounded bad... /ccboard/images/graemlins/blush.gif

Thanks for the clarification. /ccboard/images/graemlins/laugh.gif

Qtec
01-31-2005, 09:23 AM
Nice diagram but its totally wrong. /ccboard/images/graemlins/laugh.gif
Never in a million years could you hit the rail inside the 2nd diamond. In fact, with max topspin,on that shot, you would just miss the middle pocket.
I think you over estimate throw and forget to account for the margin of error. IMO, Mof E, is much more significant than throw, espescially on this shot.

Qtec
Nice dia tho.

dr_dave
01-31-2005, 10:56 AM
<blockquote><font class="small">Quote Billy_Bob:</font><hr> Playing 8-ball... I want to shoot the 1 ball into the corner pocket as shown below. But I want to know where the cue ball will hit the 8 ball after this shot and where the 8 ball will go.

Am I correct that the cue ball will travel along the green line and not the red line? (Cue ball travel path is actually 1 1/8 inches out from 1 ball?)

So in this case, this shot will make the 1 in the corner and the 8 in the side?

Would draw or follow change where the 8 would go?

(I am making the mistake of thinking the cue ball will travel along the red line and would make the 8 ball head toward the far center diamond...)

http://endeavor.med.nyu.edu/~wei/pool/

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<hr /></blockquote>
You might find the following articles useful. I think they answer your questions and more.
<ul type="square"> "The 90° rule: Part III - carom and billiard shots" (March '04 article) (http://www.engr.colostate.edu/~dga/pool/bd_articles/march04.pdf)
"The 30º rule: Part III - carom vs. cut" (June '04 article) (http://www.engr.colostate.edu/~dga/pool/bd_articles/june04.pdf)
"90º and 30º Rule Follow-up - Part II: speed effects" (March '05 article) (http://www.engr.colostate.edu/~dga/pool/bd_articles/march05.pdf)[/list]
Related articles can also be found online (http://www.engr.colostate.edu/~dga/pool/bd_articles/index.html).