The BCA league rules state that push shots are illegal and are considered a foul. I was also told that if the cue ball is kissing an object ball and if the pool ball is struck in the direction of the object ball that it would be a foul, since it would be considered a push shot. If there is space between the cue and object balls, then it would be a double kiss and a foul. I've never heard of a rule where one could not stroke towards an object ball if they were in contact. Is this correct that it's a foul in BCA league play?
BCA Rules Question
- Thread starter rostym
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FYI, I have super slow motion videos showing that the CB separates from the tip just as quickly with a frozen CB as it does with a non-frozen CB. Even though it feels very different, a frozen-CB shot (with a normal stroke) involves a non-pushing, clean hit, just like any other legal shot. For more info and super-slow-motion, see:
... but it is allowed. ???
You're right, of course - I don't know what I was thinking. Inaccurate post deleted.
pj
chgo
Just because it's interesting to me, wouldn't that just be another way of saying a super slow motion video doesn't possess the accuracy to measure the difference? The laws of physics would suggest that is the case. What a super slow motion video does show (and what would not require more accuracy in measurement) is that the cue ball separates from the object ball before it separates from the tip, or vice-versa.
Consider those two events - cue ball separates from cue tip, cue ball separates from object ball. The two events have to occur in that order for a double-hit to occur (unless there's a third event, like the cue ball hops into the air and lands on the tip). If the balls are frozen, the events would presumably (according to law of physics and different coefficients of elasticity in the two collisions) happen in the reverse order, detectable with super slow motion video.
There's an argument that can be made if all of the above is true. Can you guess where I'm heading?
No. A good high-speed camera can most certainly accurately measure tip contact time differences. For examples of measurements, see:
But even if there were small differences in tip contact time (in the thousandths of a second range), it doesn't make a difference anyway. Hitting into a frozen CB is definitely not a "push" or a "double hit."
The CB and OB remain in contact as the tip pushes and accelerates them both forward together. After the CB and OB separate from the tip (together as one, still in contact with each other), the OB then separates from the CB slightly. Here's an older video that sorta shows the effect:
A newer and better camera would show this more clearly, but the effect makes perfect physics sense, so there is no reason to question it. As the tip pushes both balls forward together, the OB starts to roll very slightly (since there is very little friction between the CB and OB as compared to between the OB and the cloth). During most of the time the tip is in contact with the CB, the CB does not rotate (because there is a lot of friction between the chalked tip and the CB). Therefore, when the CB separates from the tip, both balls have the same forward speed, but the OB has a small amount of topspin that helps it separate from the CB very slightly. So the order of separation is very clear:
- The tip separates from the CB and OB, which are still in contact.
- Then the OB separates from the CB slightly.
... but a double hit does not occur. Both balls leave together as the tip separates. Then the OB separates from the CB.
This is not detectable because it does not occur.
If everything you said were true, there might be a problem with the logic, but your assumptions are not all correct. Physics understanding (assisted by super slow motion video) usually provides the correct answers, but thank you for questioning things to help "keep the physics honest."
You restated what I said, with the caveat that "it doesn't matter". I just said there HAS to be a difference, it's just not yet measurable. And I never said it was a push or a double-hit. I said the cue ball takes longer to leave the tip when it's frozen to an object ball than when it is not. It's just not currently measurable (and I agree it's probably not significant except in theory).
So the contact point between cue ball and object ball changes (actually it disappears, I think)? How does that occur without SOME degree of separation (again, just because it's not noticeable doesn't mean it's not there, it only means we can't yet observe it).
This is the part I think you may have wrong. Your super-slow-motion video shows what looks like the tip separating first, but only because the separation that has already occurred between cue ball and object ball is currently unmeasurable and therefore undetectable. The "gap" with the tip grows faster (because the tip decelerates faster) so it LOOKS LIKE that separation happens first because it is the first to enter the currently-measurable range. Remember, the balls are moving at the same speed (they're not, we just can't measure the difference yet) and have nearly identical forces acting on them, so it makes sense that they appear to be stuck together. But they're not.
For this discussion, nothing is too small or unimportant. For the game of pool, it matters neither here nor there. It's too detailed, too nit-picky. But it's interesting.
And? I said (paraphrased) "If double-hit then the tip separated first". You responded with "not double hit". In this case, either separation could happen first.
Or do you say it does not occur because it is not yet detectable?
I actually think that in the case where the cue ball is frozen to the object ball, either separation can happen first, depending on a number of factors. For instance, if your tip is super-soft, might that affect the length of time it is in contact with the cue ball? Conversely, if it's made of a piece of cue ball ground to fit on the end of your cue, what effect would that have on the equation? Would that bring the hardness/softness of the cue itself into significance? What if the tip was made of cue ball and the shooter forgot to chalk? Now does the cue ball rotate? I also think video can answer some questions, within the boundaries of what we can measure. I don't think it's foolproof. There are many variables and a particular video only shows what happens with one specific combination of those variables.
In the end, none of this really matters to the game of pool. If the cue ball is frozen to an object ball, it is not possible under normal playing conditions with a normal forward stroke to double-hit. Something unusual, like a third ball, a rail, a hop, or a miscue that results in trapping the cue ball would have to come into play for a double-hit to result. In theory though, you can make the playing conditions whatever you want, then it becomes possible. Like I said, just because it's interesting to me.
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That is not true, based on the physical explanation in my previous post. You might not agree, but the physics is clear on this matter.
Yes. Tip hardness and shot speed affect the tip contact time for any shot per the info here:
https://billiards.colostate.edu/faq/cue-tip/contact-time/
But this has no effect on the question at hand.
Even if the tip were CB material with no chalk, the CB and OB would still separate from the tip first. However, the OB would stay in contact with the CB after tip separation since the CB and OB would have developed the same rotation (theoretically speaking, for such an extreme situation, which would never occur in real pool).
Agreed.
Agreed.
I find your analysis and demonstrations A-1. Just wondering if you have experimented with a range of off center strikes to the cueball with the balls frozen? With a vertical cue masse being the other end of the range, starting at center ball.
I have examples with different types of spin and horizontal angles here:
- HSV A.96 – Straight-on frozen cue ball shots with various types and amounts of spin
- HSV A.97 – Frozen cue ball shots with various approach angles
Although, I have not filmed highly-elevated shots.
The perfectly vertical cue at contact is an interesting study. Only suitable for players at the highest elevation. Perhaps even higher than Annapolis or West Point.
So there's an equation, based on the variables we know, for calculating the time it takes for the CB to separate from the tip (call it Tct) and another equation for calculating the time it takes for the balls to separate (Tco), and there is no combination of factors that produce a Tct that is greater than Tco? I don't know what that equation is, but one must exist or be possible to derive.
What about extreme draw, doesn't that impart a rotational force on the cue ball resulting in a linear force toward the cue and a secondary linear force on the object ball away from the cue? If executed on a very slow table with a very soft tip, could that reduce Tco to the point where Tct exceeds it? What about a "trap" shot, where the cue ball is trapped between tip and bed for some period of time? You could argue that these are not "normal forward strokes", but where do you (you specifically) draw the line? Incidentally, a trap shot executed when cue ball and object ball are not frozen is one possible way to avoid a double-hit. It's legal in APA but a foul (not a double-hit, though) in rule sets based on WPA rules. If cue ball and object ball are frozen, it's legal under WPA rules too.
What if Aramith develops some type of ball material with properties (metallic, magnetic, electrical, etc.) that allow tables to read balls (that would be great - the tables could then do the watching for close hits, scoring for matches, etc.) and some cue maker takes advantage of that to build a cue that can manipulate properties of the cue ball? It's way out there, but technology is already being developed that allows objects to extract energy from electromagnetic air waves (self-charging cell phones, for example). This technology could affect how lots of things work. Imagine being able to dial the speed of the table down or up, or being able to produce cue ball spin in any direction with a center-ball hit. Then the equations change significantly, and the game changes significantly too.
Just food for thought. Mostly my own thought.
Xeno's arrow is a famous problem that motivates calculus.
Hitting a cueball frozen to an object, not sure which branch of math these problems fall under.
RFID tags embedded in the balls, but the scanners are too slow to read in real time reliably.
Hitting a cueball frozen to an object, not sure which branch of math these problems fall under.
RFID tags embedded in the balls, but the scanners are too slow to read in real time reliably.
The perfectly vertical cue at contact is an interesting study. Only suitable for players at the highest elevation. Perhaps even higher than Annapolis or West Point.
In my recent videos with Venom, we did look at elevated jump and masse shots, but not with frozen balls:
There are equations that can predict contact times for the tip hitting a CB and the CB hitting a OB. These contact times have also been carefully and accurately measured over a wide range of tip hardnesses and shot speeds in the videos and at the links here:
But the ball contact time doesn't apply when the tip hits a CB frozen to an OB because the physics is different (as I described above) since the balls stay in contact during the entire tip contact time. The two collision are not independent since all three objects are in contact at once.
Are there two collisions, or just one? I.E., is the cue ball causing the motion of the object ball still considered a collision if they're already in contact? It's been a minute since I did this type of physics.
When the tip hits the CB frozen to an OB, there is only one collision. Most collision physics concerns two object colliding. When more than two objects are in contact at once, things are very different. You can't analyze this type of collision as separate collisions.