$100 Spin Challenge

[dr_dave]

... the effective tip offset isn't measured by where the cue points, but by where its force is directed, which, as we know, are different because of squirt.

This is a very important point. If people want more explanation and illustration, see my December '07 article (specifically, Diagram 3 and the surrounding discussion).

Regards,
Dave

 

[dr_dave]

There's a thread here somewhere in which Bob Jewett shows (maybe with a video) that a harder hit ball goes slightly longer, assuming in both cases the balls are sliding when they hit the rail.

This was a video Bob and I filmed together. Here it is:

http://billiards.colostate.edu/high_speed_videos/new/HSVB-41.htm​

The speed lengthening effect is counter to what most people believe. The reason is explained and demonstrated in the speed-related bullets and links here:

http://billiards.colostate.edu/threads/banks_and_kicks.html#effects​

Regards,
Dave

 

[Patrick Johnson]

Dave:
The equipment can make a difference. It just so happens that the difference is extremely small.

So extremely small that it makes no difference to playing pool, as the test I posted shows.

pj
chgo

 

[Colin Colenso]

This is a very important point. If people want more explanation and illustration, see my December '07 article (specifically, Diagram 3 and the surrounding discussion).

Regards,
Dave

Interesting article Dave, I hadn't seen that one before.

I see you used the terms 'actual tip offset' and 'effective tip offset' back then. I'd never encountered the terms.

Patrick's test is set up in a way that utilzes effective tip offset which would appear to guarantee near identical results, but I wonder if players' experiences are not more based upon their perception of performance relative to actual tip offsets as that is what they tend to be looking at more directly.

I'm still not sure how the 0.1% you mentioned earlier relates to that. Are you saying that a low squirt cue with 10mm actual offset would have the same result as a normal playing cue with 10.01mm actual offset? If so, that seems too low to me.

Colin

 

[dr_dave]

... The cueball will have acquired slightly more speed (in the north direction) from the squirtless cue, given the same stick speed and efficiency. Therefore, it will have rotated more during impact and this should result in a slightly greater effective tip offset and spin/speed ratio. The effect is very small in theory, but the principle, I think, is valid. Since the amount of squirt seems to be virtually independent of stick speed, the differences between sticks should probably diminish at higher speeds, since the extra rotation during impact reduces the percentage contribution of squirt.

Jim,

I'm not exactly sure what you mean by your you last (bolded) statement, but maybe your whole paragraph has something to do with the slight trend changes we saw with the squirt vs. speed data from our robot tests (see Diagram 2 in my February '08 article).

Regardless, I agree that any variation in squirt with speed is negligible (practically speaking). Now, "effective squirt" or "squerve" (the combined effects of squirt and swerve) is another story.

Regards,
Dave

 

[dr_dave]

An interesting question is whether a squirty stick can hit further out on the cueball (from the stick's perspective) without miscuing. I suspect it can.

This would seem to make sense physically because the effective offset is less with the squirty cue (see Diagram 2 in my December '07 article), but the tip must establish firm grip with the ball before the squirtiness can come into play. If the tip starts sliding immediately (before firm contact is established) due to the actual offset, maybe the miscue limit is similar for squirty vs. non squirty cues. Regardless, the difference is probably very small (and not worthy of extended discussion or testing) for practical playing cues. (... but I would still be interested to know).

Regards,
Dave

 

[Patrick Johnson]

Patrick's test is set up in a way that utilzes effective tip offset which would appear to guarantee near identical results, but I wonder if players' experiences are not more based upon their perception of performance relative to actual tip offsets as that is what they tend to be looking at more directly.

How is the player's perception of tip offset different from the "effective tip offset"? I assume you use "effective tip offset" to mean viewed in line with the desired cue ball path, as if a squirtless cue was used. I believe this is also the perception players have of it because it's the physical perspective they have (they sight along the "aim line", not the "squirt-adjusted cue line").

pj
chgo

 

[Patrick Johnson]

This would seem to make sense physically because the effective offset is less with the squirty cue (see Diagram 2 in my December '07 article), but the tip must establish firm grip with the ball before the squirtiness can come into play. If the tip starts sliding immediately (before firm contact is established) due to the actual offset, maybe the miscue limit is similar for squirty vs. non squirty cues. Regardless, the difference is probably very small (and not worthy of extended discussion or testing) for practical playing cues. (... but I would still be interested to know).

Regards,
Dave

Dave, your comment in blue above seems to contradict the notion that effective tip offset is determined by the "net direction of force", which coincides with the cue ball path (i.e., the same for all kinds of cues), which I thought you had agreed with in an earlier post here. Which am I misinterpreting?

pj
chgo

 

[dr_dave]

lower squirt is more accurate

... Lower squirt is inherently more accurate, like shooting a rifle built to closer tolerances.

I think a lot of people disagree with this, but I agree (per the graphical analysis in Diagram 2 of my December '07 article). However, when comparing typical low-squirt cues to typical regular-squirt cues, the accuracy benefit argument is not very strong. But, as I discuss in the article, the mind can be a powerful thing. Also, not all players will realize the benefits (per the "downsides" listed here).

Regards,
Dave

 

[dr_dave]

... Also complicating the question is the fact that both chalk and tip can make a difference, and it's hard to have the same tip on multiple shafts.

I think this is an important point that I don't think was brought up or discussed anywhere else in the thread. Obviously, a better tip that grabs the CB better will allow more spin to be applied (i.e., the miscue limit will be at larger offsets). So one shaft can apply more spin than another ... if it has a better tip. However, most leather tips (regardless of hardness and brand) seem to have very similar miscue limits, provided they are holding chalk.

Regards,
Dave

 

[dr_dave]

So extremely small that it makes no difference to playing pool, as the test I posted shows.

Agreed. I think your $100 is safe, practically speaking.

Regards,
Dave

 

[Colin Colenso]

How is the player's perception of tip offset different from the "effective tip offset"? I assume you use "effective tip offset" to mean viewed in line with the desired cue ball path, as if a squirtless cue was used. I believe this is also the perception players have of it because it's the physical perspective they have (they sight along the "aim line", not the "squirt-adjusted cue line").

pj
chgo

You have a point in that a player sights along the aim line, but I think when a players think about tip offsets, they will tend to imagine their perception of looking at the cue tip pointing at a distance from the center CB from their vantage.

If I'm attempting to hit the CB with a tip of english, that's how I'll perceive it. I won't be imagining the CB travel line and offsetting to that.

That said, the few degrees of squirt that is typical is not going to make significant difference in how a player visualizes hitting 1 tip or 1/2 tip or whatever english.

I think it's for kind of the same reason that Dave refered to the tip offset from the player's side as the 'actual offset' and the offset from the travel line as the 'effective offset'. The actual is what people tend to be visualizing I think, even though, it might make more sense to visualize the effective offset.

Colin

 

[Colin Colenso]

btw. Dave,
Can you give a definition of 'Actual Tip Offset'?

p.s. Hope you're back to typing with two hands.

Colin

 

[Patrick Johnson]

If I'm attempting to hit the CB with a tip of english, that's how I'll perceive it. I won't be imagining the CB travel line and offsetting to that.

"A tip of english" from what centerpoint? If you're sighting along the intended CB travel line, then "centerball" is determined by that perspective.

pj
chgo

 

[dr_dave]

Interesting article Dave

Thanks. I do aim to serve ... I also aim to swerve.

Patrick's test is set up in a way that utilzes effective tip offset which would appear to guarantee near identical results, but I wonder if players' experiences are not more based upon their perception of performance relative to actual tip offsets as that is what they tend to be looking at more directly.

I think some people are also influenced by their perception of "tips" of English, which varies with the shaft size (which is generally smaller for low-squirt shafts). For more info (artciles with illutrations), see:

http://billiards.colostate.edu/threads/English.html#tips​

I'm still not sure how the 0.1% you mentioned earlier relates to that. Are you saying that a low squirt cue with 10mm actual offset would have the same result as a normal playing cue with 10.01mm actual offset? If so, that seems too low to me.

I'll need to look at this in more detail when I return to my office next week. I'll let you know when I have specifics. Concerning the 5% and 40" numbers Mike posted previously, I don't think they apply to typical low-squirt cues.

Regards,
Dave

 

[Patrick Johnson]

I think your $100 is safe, practically speaking.

I've decided to pay it to "iusedtoberich", to show it was a serious offer and because he was the only poster who actually tried to take it seriously.

Iusedtoberich, PM me about how you'd like to collect.

pj
chgo

 

[dr_dave]

... the effective offset is less with the squirty cue ...

Dave, your comment in blue above seems to contradict the notion that effective tip offset is determined by the "net direction of force", which coincides with the cue ball path (i.e., the same for all kinds of cues), which I thought you had agreed with in an earlier post here. Which am I misinterpreting?

Both notions are correct. A cue with more squirt will have a smaller effective offset (and less spin) for a given tip offset and cue direction.

The net direction of the force does coincide with the CB path, so a cue with more squirt must be aimed along a different line to result in the same CB motion.

Sorry if I was misleading. This thread has certainly shown that this stuff is difficult to describe in terms free from misinterpretation.

Regards,
Dave

 

[dr_dave]

btw. Dave,
Can you give a definition of 'Actual Tip Offset'?

Diagram 3 in my December '07 article provides a visual definition of both "actual tip offset" and "effective tip offset." If I were in my office, I could easily post the diagram here ... sorry I can't from my current location.

p.s. Hope you're back to typing with two hands

Today is the first day I've tried. It's not easy or comfortable, and I'm sure my doctor wouldn't approve, but I can't resist.

Regards,
Dave

 

[dr_dave]

I've decided to pay it to "iusedtoberich", to show it was a serious offer and because he was the only poster who actually tried to take it seriously.

I think Bob Jewett deserves it. Maybe his post seemed a little trouble-maker-ish, but he did make some excellent points.

Regards,
Dave

 

[Colin Colenso]

"A tip of english" from what centerpoint? If you're sighting along the intended CB travel line, then "centerball" is determined by that perspective.

pj
chgo

I'm not so sure we see a line from a point, or that our heads don't align slightly differently when accounting for squirt.

Imagine playing with a cue that squirts 20 degrees. I suspect the player would favour looking down the cue line to some degree rather than getting his eyes completely behind the travel line.

Perception may also change according to whether a player pivots or addresses the line in a more parallel manner.

The reason I bring it up is because your test takes 'actual offset' out of the equation and I don't see why it should be taken out of the equation because it seems to me that actual offset is closer to the perception a player has regarding offsets.

It's obviously harder to test for though.

Colin

[edit: That said, I do think your test provides an important insight and would surprise many if they'd try it.]