Pendulum Stroke Cue Tip Trajectory

Dan White

AzB Silver Member
Silver Member
Dr. Dave did the math to illustrate the path of the tip through the ball, here:

https://www.billiards.colostate.edu/technical_proofs/new/TP_B-18.pdf

This analysis agrees with my experience in that the pendulum stroke might as well be a piston stroke anywhere near the cue ball because it just looks like the tip is traveling on a flat line. However, I was having some miscues on draw shots and I fixed the problem by moving the grip hand back a half inch or maybe an inch. Question:

1. If the analysis above were done with the hand an inch forward of perpendicular at cue ball address, what happens to the curve? In other words, does having the grip forward a little cause the cue to dip at the cue ball and explain my miscues? My guess is that it won't matter that much to cause miscues but what does the math say about that?

I believe that when I start the forward motion of the cue I tend to grip the cue tighter, raising the butt end and dipping the tip down. I think moving the grip back a little counteracts this and prevents the miscue but I wanted to learn more about item 1 before making any conclusions.

Thanks for any comments.
 
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dr_dave

Instructional Author
Gold Member
Silver Member
Dr. Dave did the math to illustrate the path of the tip through the ball, here:

https://www.billiards.colostate.edu/technical_proofs/new/TP_B-18.pdf

This analysis agrees with my experience in that the pendulum stroke might as well be a piston stroke anywhere near the cue ball because it just looks like the tip is traveling on a flat line. However, I was having some miscues on draw shots and I fixed the problem by moving the grip hand back a half inch or maybe an inch. Two questions come to mind:

1. If the analysis above were done with the hand an inch forward of perpendicular at cue ball address, what happens to the curve? In other words, does having the grip forward a little cause the cue to dip at the cue ball and explain my miscues? My guess is that it won't matter that much to cause miscues but what does the math say about that?

I believe that when I start the forward motion of the cue I tend to grip the cue tighter, raising the butt end and dipping the tip down. I think moving the grip back a little counteracts this and prevents the miscue but I wanted to learn more about item 1 before making any conclusions.

Thanks for any comments.
If your grip is ahead or behind of the perpendicular-forearm position, this just shifts the TP B-18 curve forward or backward relative to the CB. The tip still hits the ball at the desired contact point on the CB, assuming you check this careful at the "set" position with the tip close to the CB, and assuming you don't drop the elbow during the stroke into the ball.

Regards,
Dave
 

skipbales

AzB Silver Member
Silver Member
If your grip is ahead or behind of the perpendicular-forearm position, this just shifts the TP B-18 curve forward or backward relative to the CB. The tip still hits the ball at the desired contact point on the CB, assuming you check this careful at the "set" position with the tip close to the CB, and assuming you don't drop the elbow during the stroke into the ball.

Regards,
Dave

Not to question you guys who know a LOT more than I do but here are my thoughts.
The math works for a mechanical device and perfect swing which no one has. At least not all the time. Any elbow or shoulder or wrist action and all bets are off, it would seem to me. I could hit the cue ball hard with just my wrist and not even move my arm or shoulder. So it seems to me the movement of the wrist also needs to follow a pre-designed path to make the pendulum behave as prescribed. If I stroke with a pendulum stroke and simultaneously tilt my wrist forward I can force the cue tip into the cloth way early. Conversely if I cock it back as I pendulum swing forward I can scoop the ball skyward. So does the stroke assume a relaxed "natural action" wrist?

I truly LOVE all the discussion on theory and the studies and math but I have also observed that it is not at all necessary to understand what is happening to play great pool. I think of all the pros who try to explain what they do and realize it doesn't work at all as they think it does but they still play GREAT.
 

dr_dave

Instructional Author
Gold Member
Silver Member
If your grip is ahead or behind of the perpendicular-forearm position, this just shifts the TP B-18 curve forward or backward relative to the CB. The tip still hits the ball at the desired contact point on the CB, assuming you check this careful at the "set" position with the tip close to the CB, and assuming you don't drop the elbow during the stroke into the ball.
Not to question you guys who know a LOT more than I do but here are my thoughts.
The math works for a mechanical device and perfect swing which no one has. At least not all the time. Any elbow or shoulder or wrist action and all bets are off, it would seem to me. I could hit the cue ball hard with just my wrist and not even move my arm or shoulder. So it seems to me the movement of the wrist also needs to follow a pre-designed path to make the pendulum behave as prescribed. If I stroke with a pendulum stroke and simultaneously tilt my wrist forward I can force the cue tip into the cloth way early. Conversely if I cock it back as I pendulum swing forward I can scoop the ball skyward. So does the stroke assume a relaxed "natural action" wrist?
If your wrist is bent or flexed differently at CB contact compared to at your set position, you obviously won't hit the CB where you are aiming to hit it. Also, wrist motion during the stroke will affect the path of the cue tip. However, for most people with good technique, and for most shots, the wrist does not move very much during the stroke. If it does, a different analysis would be required.


I truly LOVE all the discussion on theory and the studies and math but I have also observed that it is not at all necessary to understand what is happening to play great pool. I think of all the pros who try to explain what they do and realize it doesn't work at all as they think it does but they still play GREAT.
Agreed. A great player doesn't need to be able to truly understand or accurately explain very much to be able to play great. But with many instructors, and with many participants on AZB, the understanding and ability to explain are valued. Although, I would never show a student a pool physics analysis (unless they really begged me to show it to them).

Regards,
Dave
 

skipbales

AzB Silver Member
Silver Member
If your wrist is bent or flexed differently at CB contact compared to at your set position, you obviously won't hit the CB where you are aiming to hit it. Also, wrist motion during the stroke will affect the path of the cue tip. However, for most people with good technique, and for most shots, the wrist does not move very much during the stroke. If it does, a different analysis would be required.

Regards,
Dave

I remember using a lot of wrist to try to create a piston shot. My goal then was straight level and I let the wrist flex a lot to keep the stick straight. That was years ago before I learned the wonders of the pendulum stroke from all of you guys.

Agreed. A great player doesn't need to be able to truly understand or accurately explain very much to be able to play great. But with many instructors, and with many participants on AZB, the understanding and ability to explain are valued.
Dave
Learning so much from your series with actual facts and demonstrations to back things up helps me keep the rest of what I see and hear in proper perspective. It sometimes gets me in trouble when I make a comment without thinking. Especially when the player the comment is aimed at is supposed to be a better player. Being a better player doesn't mean they know what is going on. My playing partner hit a long shot from close to the rail (elevated butt end) slow speed and a ton of low left. He missed the ball left and said "the deflection got me". Actually the deflection tried to save him but the swerve killed him. The deflection would have sent the cue ball to the right and hit the object ball too full. He completely missed the ball by 1/4" to the left. My tongue still hurts from biting it.:wink:
 
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