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View Full Version : cue ball direction for an angled, frozen push shot



dr_dave
07-29-2005, 10:56 AM
FYI, I just posted an analysis that compares two aiming systems for determining the cue ball path for a push shot, where the cue ball is frozen to an object ball. One system is a 2/3-angle approximation and the other is the Jewett interference system. I compare both systems to experimental results from HSV A.97 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-97.htm). You can see explanations and illustrations of the methods along with a plot of the results in TP A.15 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-15.pdf) on my website (http://www.engr.colostate.edu/~dga/pool/).

Enjoy,
Dr. Dave

PS: The Jewett system matches the experimental results very closely. Good job, Bob!

Bob_Jewett
07-29-2005, 01:45 PM
<blockquote><font class="small">Quote dr_dave:</font><hr>... determining the cue ball path for a push shot, where the cue ball is frozen to an object ball. ...

I compare both systems to experimental results from HSV A.97 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-97.htm).<hr /></blockquote>
A small nit on terminology. Different people use the term "push" differently. A push shot at pool is illegal. A shot through a frozen ball is not illegal at pool.

There seems to be something wrong with the experimental results. The angle for a 90-degree cut must be 90-degrees, but it's shown as less than 80. It's hard to estimate this angle accurately when doing the experiment.

There is a first-order correction that can be applied to the "two times fuller" interference system. Instead of the line of centers of the two frozen balls as the reference line, use the line that the object ball will be thrown along. Also, it's important in the experiment to be sure that there is no follow or draw on the cue ball. It is not so easy to have no follow or draw.

dr_dave
07-29-2005, 02:27 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr>A small nit on terminology. Different people use the term "push" differently. A push shot at pool is illegal. A shot through a frozen ball is not illegal at pool.<hr /></blockquote>
Your point is well taken. I've always thought of a frozen cue ball shot as a legal push shot, but I can see how that can be misleading to some.

<blockquote><font class="small">Quote Bob_Jewett:</font><hr>There seems to be something wrong with the experimental results. The angle for a 90-degree cut must be 90-degrees, but it's shown as less than 80. It's hard to estimate this angle accurately when doing the experiment.<hr /></blockquote>There is no error, but 0-degree and 90-degree cuts were not included in HSV A.97 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-97.htm). The cut angles varied between only about 8 and 77 degrees. But I agree with you that a full hit (0-degree cut) would have a target angle of 0, and a tangent line hit (90-degree cut) would have a 90-degree target angle. FYI, I just added these obvious extreme points to the plot in TP A.15 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-15.pdf) so the results would not be misleading. Thank you for pointing this out.

<blockquote><font class="small">Quote Bob_Jewett:</font><hr>There is a first-order correction that can be applied to the "two times fuller" interference system. Instead of the line of centers of the two frozen balls as the reference line, use the line that the object ball will be thrown along.<hr /></blockquote>
Thanks. That's useful info.

<blockquote><font class="small">Quote Bob_Jewett:</font><hr>Also, it's important in the experiment to be sure that there is no follow or draw on the cue ball. It is not so easy to have no follow or draw.<hr /></blockquote>
Actually, a small amount of follow was used on all of the shots in HSV A.97 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-97.htm). What effect would you expect this to have on the results?

Thanks,
Dave

Bob_Jewett
07-29-2005, 03:22 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> ...
Actually, a small amount of follow was used on all of the shots in HSV A.97 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-97.htm). What effect would you expect this to have on the results?
... <hr /></blockquote>
It has the same kind of effect as follow (or draw) on any other carom shot -- it will cause the path of the cue ball to curve after the ball leaves the other ball (and the tip).

dr_dave
07-30-2005, 10:19 AM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> ...
Actually, a small amount of follow was used on all of the shots in HSV A.97 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-97.htm). What effect would you expect this to have on the results?
... <hr /></blockquote>
It has the same kind of effect as follow (or draw) on any other carom shot -- it will cause the path of the cue ball to curve after the ball leaves the other ball (and the tip). <hr /></blockquote>
I asked because I couldn't see any follow effect with the shots we filmed. The effect must be really small, especially at larger cut angles. (There is also negligible effect at very small cut angles.) I think the follow effect is small because the CB is "pushed" so much in the aiming line direction.

Regards,
Dave