OB on the rail & CIT?

[dr_dave]

Dr. Dave,

Many thanks for taking the time to do the test, for doing it so carefully (although we wouldn't expect anything else), and then describing it so precisely.

Thank you for you graciousness ... I appreciate it. I was happy to do the experiment ... it was fun and I was curious to see the results.

On the possibility that an explanation might be had short of the full FEA treatment, I'm still holding out some hope that gearing may be limiting the throw in the frozen ball case. Bob has a tough objection to that, but I have a counter argument...not a killer counter argument to be sure, but one of sorts (i.e., a "considerable'" time/phase lag between the forces acting at the two interfaces).

That argument could also make the case that the CB would not limit the gearing, right? It is possible the thrown OB leaves the collision before the full effect of the CB reaction to the rotation is felt. On the other hand, there is clear evidence that a 3-ball collision responds differently than two independent 2-ball collisions. A good example is the shot in Diagram 4 of:

"Ball Weight and Size Difference Effects – Part I" (February, 2012)​

This might tend to back up your argument that the CB might be able limit the gearing motion some during the collision.

While this would be impossible to prove in a quantitative fashion, obviously, some of your high-speed videos may directly answer the question as to how free the first object ball is to spin. I'll be looking at them very carefully tomorrow.

I honestly doubt my high-speed videos will provide you with any insight regarding this situation, but I'll be happy to see if you can find some useful evidence from them.

Regards,
Dave

 

[Jal]

Thank you for you graciousness ... I appreciate it. I was happy to do the experiment ... it was fun and I was curious to see the results.

My part was easy so I raise my thanks by 10X.

That argument could also make the case that the CB would not limit the gearing, right?

Yes, that's in fact what I'm suggesting might be true. If so, the gearing would limit the amount of throw of the second object ball and explain why "we" didn't see much more.

It is possible the thrown OB leaves the collision before the full effect of the CB reaction to the rotation is felt. On the other hand, there is clear evidence that a 3-ball collision responds differently than two independent 2-ball collisions. A good example is the shot in Diagram 4 of:

"Ball Weight and Size Difference Effects – Part I" (February, 2012)​

On the old RSB forum, I thought I had an end-around the n-body problem for the purpose of explaining a particular phenomenon. Mr. J (whose first name is Bob) quickly corrected me and I thought I should never get near it again, much less under his and your watchful eyes. I just don't understand these simultaneous collisions and tend to get dizzy thinking about them.

Nevertheless (oh boy), I'm thinking the peak force between the two object balls, for instance, occurs later (and maybe considerably later, relatively speaking) than between the cueball and the first object ball. This could "free up" the first object ball to spin enough so that gearing between it and the second object ball could take place (i.e., the cueball-object ball force has subsided substantially as the two object balls are really getting into it).

A couple of years ago I looked at the time averaged displacement of an object subjected to various symmetric forces (e.g., square pulse, sine and a few others) during a "collision." (In other words, the integral of xdt/T from 0 to T). The values all fall within a narrow range, about one-quarter to one-third of the object's final displacement at the termination of the collision. So with the three-ball collision, I'm thinking that during a substantial part of the cueball-first object ball interaction, there is, on average, relatively little penetration of the second object ball's "space" by the first object ball. Thus, a "considerable" phase lag should be occurring in the buildup of that force. (Of course, in general, that's why we have wave propagation instead rigid bodies.)

I don't mean to be insulting with what is pretty much trivial for you (and Bob and others), but just trying to offer some motivation for this line of thought on why the first object ball might achieve gearing with the second one. If you or he (or anyone) can immediately disabuse me of this...

I honestly doubt my high-speed videos will provide you with any insight regarding this situation, but I'll be happy to see if you can find some useful evidence from them.

I will be looking.

Jim

 

[dr_dave]

That argument could also make the case that the CB would not limit the gearing, right?

Yes, that's in fact what I'm suggesting might be true. If so, the gearing would limit the amount of throw of the second object ball and explain why "we" didn't see much more.

Jim, I'm in Bob's "camp" on this one. I think the CB is still in contact with the 1st OB while it is interacting with the 2nd frozen OB.

For small cut angles, where the OBs gear during the collision, it would seem that the interaction of the CB might tend to reduce the throw a little since it would reduce the gearing spin some by reacting against it. Even with larger cut angles (like the 30 degrees in my experiment), this effect might still tend to decrease throw slightly. There is no gearing between the OBs at this angle (at the shot speed I used) ... the balls are sliding during contact. The CB interaction would tend to slow the rotation that develops in the 1st OB as it interacts with the 2nd OB. This would tend to increase the relative sliding speed between the OBs. I would expect that to reduce the dynamic friction COR (since friction is less at faster sliding speeds with pool balls). What do you and Bob think about this possible effect? It doesn't predict what is observed in the experiment, but it might be a piece of the "big picture" puzzle.

... there is clear evidence that a 3-ball collision responds differently than two independent 2-ball collisions. A good example is the shot in Diagram 4 of:

"Ball Weight and Size Difference Effects – Part I" (February, 2012)​

This might tend to back up your argument that the CB might be able limit the gearing motion some during the collision.

Nevertheless (oh boy), I'm thinking the peak force between the two object balls, for instance, occurs later (and maybe considerably later, relatively speaking) than between the cueball and the first object ball. This could "free up" the first object ball to spin enough so that gearing between it and the second object ball could take place (i.e., the cueball-object ball force has subsided substantially as the two object balls are really getting into it).

Jim, I don't think this is the case. I think the 1st OB is sandwiched between the CB and frozen OB as the forces develop and change at both contact points. I think this effect is what drives the 1st OB forward in Diagram 4 in my article (even with equal-weight balls). The CB might still be pushing the 1st OB forward after the 2nd OB leaves. What do you, Bob, and others think about this?

I don't mean to be insulting with what is pretty much trivial for you (and Bob and others)

This problem is not trivial at all, and I think our understanding of the detailed physics during the multiple collisions is probably not very complete. All that is certain is the results of the experiment ... a stunned ball seems to throw about the same amount as a frozen ball.

Regards,
Dave

 

[Jal]

Jim, I'm in Bob's "camp" on this one. I think the CB is still in contact with the 1st OB while it is interacting with the 2nd frozen OB.

I certainly would agree, but then there's the possibility of the phase delay I indicated earlier.

For small cut angles, where the OBs gear during the collision, it would seem that the interaction of the CB might tend to reduce the throw a little since it would reduce the gearing spin some by reacting against it.

If the CB completely prevented the object balls from gearing, wouldn't you see larger throw since gearing marks the end of sliding friction? I don't see it reducing the gearing spin, but either preventing it, or not. But I'll have to think about this more (or get further explication from you).

Even with larger cut angles (like the 30 degrees in my experiment), this effect might still tend to decrease throw slightly. There is no gearing between the OBs at this angle (at the shot speed I used) ... the balls are sliding during contact.

If you would take a look at videos HSVA 88, 89, 94 and 95 (three of which are 45-degree impacts), it looks to me that both object balls come away with the same or nearly the same sidespin (i.e., they could be gearing or fairly close to it). We can't see the impacting cueball, so it is possible that it may have had some spin on it, or contacted the first OB off-center, thus inducing some or all of the spin we see on the first object ball.

The CB interaction would tend to slow the rotation that develops in the 1st OB as it interacts with the 2nd OB. This would tend to increase the relative sliding speed between the OBs. I would expect that to reduce the dynamic friction COR (since friction is less at faster sliding speeds with pool balls). What do you and Bob think about this possible effect? It doesn't predict what is observed in the experiment, but it might be a piece of the "big picture" puzzle.

For what it's worth, I agree. I still see a possibility, though, that because the first object ball is coming up to speed, the COF between it and the second OB might be large enough to bring them into gearing if there's enough of a time period when the force between them is larger than the force between the CB and the first OB (if such a period exists to any significant extent).

Jim, I don't think this is the case. I think the 1st OB is sandwiched between the CB and frozen OB as the forces develop and change at both contact points. I think this effect is what drives the 1st OB forward in Diagram 4 in my article (even with equal-weight balls). The CB might still be pushing the 1st OB forward after the 2nd OB leaves. What do you, Bob, and others think about this?

Well, one thing I can say for sure is that the impulse between the cueball and first object ball is larger than the impulse between the two OBs. How to parcel this out between the average forces and the time of contact is another matter. I'd welcome any further thoughts from you or Bob or anyone that has some ideas. My suspicion is that it's the average force (averaged over the time of contact) that's larger, because the cueball runs into two balls, whereas the first object ball only runs into one. But this is the sort of thing that rapidly gets confusing.

I'm not pushing this explanation for your throw results, just pursuing it until it might become more obvious that it does or doesn't make sense.

Jim

 

[LAMas]

Well my 2 cents.

With gears, there is lash, for gears cannot be welded together in order to rotate - for long, so there must be a small clearance between the teeth of both gears – lash. Starting from a quiescent position, when the driving gear rotates, it takes a finite time and distance for the driving tooth to contact the driven tooth before the driven gear starts to rotate.

Could the frozen OBs be considered welded together with no lash when the first OB is driven by the CB? When the unfrozen OB, driven by the CB, contacts the 2nd OB, could there be a similar lash/lag before they are fully meshed together?

Could this account for the throw angle for the 2nd frozen OB to be larger than the unfrozen 2nd OB with said lash/lag?

The transfer of energy from the unfrozen OB to the 2nd OB must be cumulative for an off center hit, say CTE, and not instantaneous as would be for a center CB to center OB hit.

I think this is a calculus problem – a class that I flunked. :smile:

 

[dr_dave]

I certainly would agree, but then there's the possibility of the phase delay I indicated earlier.

There are certainly delays due to the time it takes for elastic waves to travel between the contact areas, but this happens very quickly. From speed of sound data, the elastic wave speed in pool balls is probably close to 4000 m/s. From Marlow's experiments, ball contact times are probably close to 0.0003 seconds. During that time, the waves have time to travel back and forth across the 1st OB at least 20 times. From these rough calculations (please check my math), I would say the "phase lag" is not very significant.

If the CB completely prevented the object balls from gearing, wouldn't you see larger throw since gearing marks the end of sliding friction?

Per the derivation and discussion leading up to Equation 14 in TP A.14, gearing indicates that as much throw as possible has been created, regardless of the COF. Therefore, if gearing is resisted, less throw might result. Right?

If you would take a look at videos HSVA 88, 89, 94 and 95 (three of which are 45-degree impacts), it looks to me that both object balls come away with the same or nearly the same sidespin (i.e., they could be gearing or fairly close to it). We can't see the impacting cueball, so it is possible that it may have had some spin on it, or contacted the first OB off-center, thus inducing some or all of the spin we see on the first object ball.

The CB should not have any significant (if any) sidespin in those shots. I agree that the spins on both OBs seem about the same, but that would indicate to me that the balls were not gearing. Because the 1st ball is moving down in the frame, it would need to have more spin than the 2nd ball for gearing. The extra spin would be required to counteract the translational speed to result in no sliding (i.e., "gearing") at the contact point. Right? A 45 degree cut is definitely well into the non-gearing (sliding) portion of the throw curves in TP A.14.

Well, one thing I can say for sure is that the impulse between the cueball and first object ball is larger than the impulse between the two OBs.

Agreed.

I'm not pushing this explanation for your throw results, just pursuing it until it might become more obvious that it does or doesn't make sense.

To me, it kind of makes sense that a stunned ball should throw the same amount as a frozen combo, and the experiment kind of backs that up. The resistance to gearing must be a small/insignificant effect; otherwise, the experiment would have shown a greater difference (unless there is some counteracting effect that we still have not identified convincingly).

Regards,
Dave

 

[dr_dave]

With gears, there is lash, for gears cannot be welded together in order to rotate - for long, so there must be a small clearance between the teeth of both gears – lash. Starting from a quiescent position, when the driving gear rotates, it takes a finite time and distance for the driving tooth to contact the driven tooth before the driven gear starts to rotate.

"Backlash" in actual gears is a very different phenomenon. The delay is cause when the direction of rotation is reversed and a gear tooth needs to cross a clearance gap before contacting an adjacent tooth. This doesn't happen with pool balls that maintain surface contact during a collision and don't reverse direction and don't have teeth with clearances. Nice try though.

Regards,
Dave

 

[LAMas]

"Backlash" in actual gears is a very different phenomenon. The delay is cause when the direction of rotation is reversed and a gear tooth needs to cross a clearance gap before contacting an adjacent tooth. This doesn't happen with pool balls that maintain surface contact during a collision and don't reverse direction and don't have teeth with clearances. Nice try though.

Regards,
Dave

Dave,
I wrote "lash" (Gear lash is the amount one gear moves while the other is held stationary; it is a measure of the gap between the gear faces) and not "BACKlash". Nice try though.:smile:

I didn't write or infere a reversal of rotation as in backlash.

Still it wasn't a good analogy for untill the two gear faces touch each other, there is no transfer of energy. By design, when they touch, there is an immediate transfer of energy.

When 2 OB are frozen together, they are meshed and the transfer of energy is immediate.

When the two OBs are separated, there is a cumulative transfer of energy when they first come in contact with each other untill they accumulate enough pressure against each other (as the first OB progressivly compresses itself into the second) to move the second OB.
----------------------------------

With respect to my original question, I tried a CTE hit, with stun, on a frozen to the rail OB and the OB seemed to come off of the rail at a slight angle.

 

[dr_dave]

I wrote "lash" (Gear lash is the amount one gear moves while the other is held stationary; it is a measure of the gap between the gear faces) and not "BACKlash".

To me, it is the same thing. It occurs (forward or backward) only when there is a gap between the teeth. I think the terms "backlash" and "lash" are sometimes used interchangeably (see the Wikipedia backlash page). Regardless, we are talking about the same effect. However, once contact is initiated and maintained, there is no longer any lash (unless the direction of rotation is reversed).

when they touch, there is an immediate transfer of energy.

Agreed.

When 2 OB are frozen together, they are meshed and the transfer of energy is immediate.

Agreed.

When the two OBs are separated, there is a cumulative transfer of energy when they first come in contact with each other untill they accumulate enough pressure against each other (as the first OB progressivly compresses itself into the second) to move the second OB.

The balls begin creating contact force (and begin transferring momentum) immediately after they initiate contact. This force does grow to a maximum during the contact time as the compression increases, but there is force (and momentum transfer) during the entire contact time. This is the same as with gear teeth.

With respect to my original question, I tried a CTE hit, with stun, on a frozen to the rail OB and the OB seemed to come off of the rail at a slight angle.

That is certainly to be expected, more so at slower speeds and clingy conditions.

Regards,
Dave

 

[dr_dave]

With respect to my original question, I tried a CTE hit, with stun, on a frozen to the rail OB and the OB seemed to come off of the rail at a slight angle.

Have you tried the spit and chalk tricks demonstrated in the following video:

NV B.91 - Frozen-throw-down-rail proposition shot, from VEPS V​

The difference between a near throwless hit and a clingy hit is very dramatic.

Be sure to keep those balls clean.

Regards,
Dave (provider of free hygiene advice)

 

[LAMas]

Dave,
I saw that vid of your's...tricky.:smile:

 

[dr_dave]

Dave,
I saw that vid of your's...tricky.:smile:

The chalk smudge experiment reminds me of conditions at one of the bars we play at in my league. The balls are so old, beat up, and filthy, I am afraid to hit any cut shot (along the rail or not) without gearing outside English. Cling is a regular occurrence at that place.

Catch you later,
Dave

 

[LAMas]

Very few bars that I know of have ball cleaners. You have to wipe them yourself if you want or need to.

Putting the chalk face down on the table or chalking over it often happens in bars.