I just realized how much I didn't know.
physics-based draw shot advice
- Thread starter dr_dave
- Start date
Awesome info.
I found the info on long distance draw especially interesting. I think I knew this subconsciously but never noticed it until now. I'm not sure what the physics are or how to express this, but it feels like a closer to center draw stroke may have less initial backspin, but it's sorta 'weightier' backspin and holds up longer over time and distance. Whereas those ultra low hits are going to wear off after a point, which is why they're nice for those short controlled draw shots.. you know you can't overcook the draw and end up with terrible shape because there's only so much work backspin alone can do. I guess to put it another way, if erring on the side of caution means not overdrawing it, then lower and soft is better than higher and firm.
Some questions:
1. Draw seems harder to control than follow, but why? Like if you shoot from somewhere near the corner at a straight-in ball in the center of the table, and you try to follow all the way across the table to scratch in the opposite corner (where the OB dropped), you will succeed on that scratch fairly often. But try to pocket the CB by drawing into the corner nearest you and it doesn't succeed as often. What's doing on there?
2. Does draw+sidespin carry the ball a little bit in the direction of the sidespin on any shot? I know center+sidespin won't, but I sort of picture draw and side whirling on a diagonal axis. If the CB's momentum is mostly killed at the moment of impact, it seems like that diagonal spin would carry the ball away at a different angle than pure backspin.
Ex: Let's say you have a cut of around 15-20 degrees. You're sending the OB to the right. You want to draw as straight back as possible, minimizing how far left the CB goes as it draws backwards. Is this accomplished with pure centerball draw? Would low left be ideal to throw in the OB, therefore you can cut it less, therefore straighter draw? Or would low right somehow alter the backspin direction and carry it more right?
I found the info on long distance draw especially interesting. I think I knew this subconsciously but never noticed it until now. I'm not sure what the physics are or how to express this, but it feels like a closer to center draw stroke may have less initial backspin, but it's sorta 'weightier' backspin and holds up longer over time and distance. Whereas those ultra low hits are going to wear off after a point, which is why they're nice for those short controlled draw shots.. you know you can't overcook the draw and end up with terrible shape because there's only so much work backspin alone can do. I guess to put it another way, if erring on the side of caution means not overdrawing it, then lower and soft is better than higher and firm.
Some questions:
1. Draw seems harder to control than follow, but why? Like if you shoot from somewhere near the corner at a straight-in ball in the center of the table, and you try to follow all the way across the table to scratch in the opposite corner (where the OB dropped), you will succeed on that scratch fairly often. But try to pocket the CB by drawing into the corner nearest you and it doesn't succeed as often. What's doing on there?
2. Does draw+sidespin carry the ball a little bit in the direction of the sidespin on any shot? I know center+sidespin won't, but I sort of picture draw and side whirling on a diagonal axis. If the CB's momentum is mostly killed at the moment of impact, it seems like that diagonal spin would carry the ball away at a different angle than pure backspin.
Ex: Let's say you have a cut of around 15-20 degrees. You're sending the OB to the right. You want to draw as straight back as possible, minimizing how far left the CB goes as it draws backwards. Is this accomplished with pure centerball draw? Would low left be ideal to throw in the OB, therefore you can cut it less, therefore straighter draw? Or would low right somehow alter the backspin direction and carry it more right?
Boostaholic
Registered
Dave, I have always wondered about hitting the CB lower and the drag thats happeningdr_dave said:
Is the force applied to the CB not always straight forward, I know if you hit above center enough as in a follow shot the force drives it down and rebounds the CB off the slate enough to clear a coin or more even though a lot of people don't realize it.
Can the same happen for near miscue line draw shots where the friction of the cloth does not play a big role because the CB is getting less contact for a duration?
I doubt this, but it doesn't matter.
There's no "impact" in this description, so it isn't a true analogy. But the principle is the same anyway: whatever tip speed you can achieve while in contact with the CB is what matters, impact or not.
pj
chgo
This illustrates that the CB "cares about" what?
What does that have to do with this?
pj
chgo
Good draw requires an accelerating cue (stick). The speed at contact is irrelevant. The speed of the cue at loss of contact is the key issue.
If you misunderstood my experiment, it was a "limiting case." Move the cue tip a millimeter away from the cue ball and do the same experiment. At contact the cue is moving mighty slowly. At loss of contact, a fraction of a second later because the cue is accelerating, the cue is humming right along. Draw!
Consider trying to draw by throwing a one-ounce cue into the cue ball. Then try pushing it through, reaching the same speed as that at which you threw the cue. The latter might produce draw. The former bounces off the cue ball. (Don't try this at home, it's a thought experiment.)
Nick
If you misunderstood my experiment, it was a "limiting case." Move the cue tip a millimeter away from the cue ball and do the same experiment. At contact the cue is moving mighty slowly. At loss of contact, a fraction of a second later because the cue is accelerating, the cue is humming right along. Draw!
Consider trying to draw by throwing a one-ounce cue into the cue ball. Then try pushing it through, reaching the same speed as that at which you threw the cue. The latter might produce draw. The former bounces off the cue ball. (Don't try this at home, it's a thought experiment.)
Nick
....SPF=randyg
Thanks.CreeDo said:
Me too.CreeDo said:
When you hit the ball lower, the ball gets more spin but less speed. More drag (and spin loss) occurs because of the slower speed.CreeDo said:
I think one reason is: you need more power for the draw shot, and many people are less accurate with more power. More reasons can be found here:CreeDo said:
Check out the articles from me and Bob linked here:CreeDo said:
They don't cover the backspin case directly, but I think the general principles still apply.
Also, see:
I hope that helps.
Excellent questions!!!
Regards,
Dave
FYI, I have a good video demo of this here:Boostaholic said:
I think cue elevation and the amount of squirt up can effect the draw action, but I have not studied this enough yet to fully understand it. Some related info can be found here:Boostaholic said:
Regards,
Dave
I think Koehler's book is excellent. I used it as a resource when I was working on my book. However, I don't agree with his statements about acceleration. Cue speed, not acceleration, is what gives the CB speed and spin. Most people accelerate very little at ball impact. And acceleration during impact will have negligible effect with a normal pool stroke anyway. Actually, if you accelerate too late, you have lost the opportunity to create more cue speed (by accelerating earlier). For more info, see the video, article, and analysis links here:nickgeo said:
Having said all of this, the advice to "accelerate into the ball" might actually help some people create a smoother stroke with more cue speed and a good resulting follow through. But again, the final cue speed (just before impact), and the tip offset, are what are important.
Regards,
Dave
dr_dave said:
Thanks Dave.
Interested in the pronounced flattenening of w (spin) at high b for an inelastic tip.
When I look at your equation for the effect of inelasticity on w, it seems the effects are all in v, i.e., w = stuff*v with the tip efficiency buried in v. This means your equations say tip efficiency has no effect on w/v, the spin-to-speed ratio and in particular how w/v depends on b.
The graphs in your analysis seem to tell a different story.
In going from 80% to 100% of miscue limit, the elastic tip seems to decrease v by 10-15% and increase w by 20% or so.
With the inelastic tip v is decreased by a similar proportion while w is barely increased...
thoughts?
I was also a little surprised by this.mikepage said:
That's correct. See Equations 3, 4, and 6 in TP A.30. The relationship between CB spin and speed is not affected by energy. It is a direct result of momentum principles. The spin-rate factor (SRF = w / (v/R)) is:mikepage said:
SRF = (5/2)(b/R)
At b_max = R/2, SRF = 1.25.
I think this is an "optical illusion."mikepage said:
:grin: The curves seem to tell one story, but the ratio remains directly proportional to tip offset for both perfect and inelastic tips. To be sure, I temporarily added spin-rate-factor plots to my analysis file (but I didn't post it). Sure enough, both plots were straight lines. I also checked the ratio at the maximum offset for both cases, and both numbers were 1.25. Unless I am missing something, I think everything is hunky-dory. Please let me know if you still think otherwise.
Regards,
Dave
PS: Thank you for taking an in-depth look at my document. I'm glad there's a few people out there (you, Jal, Bob, PJ, others) who can "check my work."
Thanks. I feel much more confident with the results now that many experienced people have provided some support and validation. l still wish I had a robot with which I could provide conclusive proof with real cues and real balls and accurate and repeatable tip placement and cue speed. Hopefully, we will have such proof one day.spoons said:
Regards,
Dave