Tip hardness and the amount of spin. Is the physics really settled?

[ineedaspot]

I recently got into a discussion about whether a soft tip actually results in more spin. The best pool physics resource I know of at colostate says that this is a myth:

http://billiards.colostate.edu/threads/cue_tip.html#hardness

I understand the physics of the argument, but I'm still not convinced. First of all, my personal experience says otherwise. If I hit the same shot, same stroke, I get noticeably more draw with a softer tip. One can argue that maybe if I had a better stroke this wouldn't happen, but even if that is the case, it still means that the tip hardness does affect spin. I fully agree that personal experience doesn't mean much scientifically. But it doesn't mean nothing. And I'm not the only person who has experienced this -- most experienced players I've spoken to agree with this assessment.

The claim that hardness doesn't affect spin is based on a model that treats the contact between tip and ball as single instantaneous impulse, where tip hardness only affects the coefficient of restitution, and the duration of contact, but not the direction of the force applied. OK, this is a plausible model, and it is true that the tip and ball don't stay in contact for very long, but still, this isn't what actually happens. What actually happens is that the tip deforms (and the shaft bends slightly), and the force applied to the ball is primarily the result of the tip resisting this deformation and returning to its original shape.

Like I said, modelling the contact as instantaneous might turn out to be accurate, but this is by no means obvious, at least not to me. The tip is a strangely-shaped thing, thicker in the middle than on the sides, and for an off-center hit, it doesn't deform straight back, it deforms a little bit sideways due to the friction and the fact that the ball surface is at an angle.

To really figure out what's going on would require a detailed computer model of the compression of the tip. This is a complicated thing, and it's not clear offhand what the results would be. For example, I'm not even certain that the force vector from the tip to the ball would point in roughly the same direction throughout the contact.

One way to think about problems like this is to do extreme thought experiments. As it happens, the colostate page links to an actual experiment where someone made a tip out of a rubber super ball. The results were much more english (and also much more deflection).
http://www.waynesthisandthat.com/billiards.htm#super tip

Obviously, a soft leather tip is not the same as a rubber tip, but the rubber experiment does show that, with some parameters, the instantaneous impulse model does indeed fall apart. So the question is, do whatever effects that occur with a rubber tip also occur with a soft leather tip to a lesser degree.

I'd be interested what the other physics geeks here think about this topic. One thing that I would find convincing, or at least perplexing, would be some kind of controlled robot experiment showing that that tip consistency doesn't affect draw, at least not in the range of normal leather tips.

 

[SilverCue]

I recently got into a discussion about whether a soft tip actually results in more spin. The best pool physics resource I know of at colostate says that this is a myth:

http://billiards.colostate.edu/threads/cue_tip.html#hardness

I understand the physics of the argument, but I'm still not convinced. First of all, my personal experience says otherwise. If I hit the same shot, same stroke, I get noticeably more draw with a softer tip. One can argue that maybe if I had a better stroke this wouldn't happen, but even if that is the case, it still means that the tip hardness does affect spin. I fully agree that personal experience doesn't mean much scientifically. But it doesn't mean nothing. And I'm not the only person who has experienced this -- most experienced players I've spoken to agree with this assessment.

The claim that hardness doesn't affect spin is based on a model that treats the contact between tip and ball as single instantaneous impulse, where tip hardness only affects the coefficient of restitution, and the duration of contact, but not the direction of the force applied. OK, this is a plausible model, and it is true that the tip and ball don't stay in contact for very long, but still, this isn't what actually happens. What actually happens is that the tip deforms (and the shaft bends slightly), and the force applied to the ball is primarily the result of the tip resisting this deformation and returning to its original shape.

Like I said, modelling the contact as instantaneous might turn out to be accurate, but this is by no means obvious, at least not to me. The tip is a strangely-shaped thing, thicker in the middle than on the sides, and for an off-center hit, it doesn't deform straight back, it deforms a little bit sideways due to the friction and the fact that the ball surface is at an angle.

To really figure out what's going on would require a detailed computer model of the compression of the tip. This is a complicated thing, and it's not clear offhand what the results would be. For example, I'm not even certain that the force vector from the tip to the ball would point in roughly the same direction throughout the contact.

One way to think about problems like this is to do extreme thought experiments. As it happens, the colostate page links to an actual experiment where someone made a tip out of a rubber super ball. The results were much more english (and also much more deflection).
http://www.waynesthisandthat.com/billiards.htm#super tip

Obviously, a soft leather tip is not the same as a rubber tip, but the rubber experiment does show that, with some parameters, the instantaneous impulse model does indeed fall apart. So the question is, do whatever effects that occur with a rubber tip also occur with a soft leather tip to a lesser degree.

I'd be interested what the other physics geeks here think about this topic. One thing that I would find convincing, or at least perplexing, would be some kind of controlled robot experiment showing that that tip consistency doesn't affect draw, at least not in the range of normal leather tips.

I'm in the process of experimenting with draw and so far, it seams:
1. When using a soft or medium stroke, soft or medium tips draw further.
2. But for power draw, my Tiger Jump Break tip works best.

But since I'm using different shafts, this doesn't mean much.

http://billiards.colostate.edu/threads/cue_tip.html#contact

If you start here and scroll down, you can see a similar discussion:
http://forums.azbilliards.com/showthread.php?p=5175398#post5175398

 

[MitchAlsup]

I understand the physics of the argument, but I'm still not convinced. First of all, my personal experience says otherwise. If I hit the same shot, same stroke, I get noticeably more draw with a softer tip.

What about all of us who use hard tips and get great draw--like up to 12 diamonds worth.

 

[jojopiff]

What about all of us who use hard tips and get great draw--like up to 12 diamonds worth.

This has absolutely nothing to do with the OP. If your statement is I can draw 12 diamonds with a hard tip but only 8 with a soft tip then it's relevant. Otherwise, it's simply bragging how far you can draw the ball and is as relevant to this particular discussion as me saying I don't like the taste of milk.

To the OP, Having used a hard tip most of my life, my only use of a soft tip is on the rare occasion I'm hitting with someone elses cue. And if I am doing that I'm not power draw/following anything. But, on the balls I do hit with a soft or medium stroke, I do find I get more action than I'm used to. This could be caused by ANY number of things though, but I couldn't rule out that a softer tip moves the cue ball less.

 

[ineedaspot]

What about all of us who use hard tips and get great draw--like up to 12 diamonds worth.

No doubt it's possible to get great draw with either kind of tip. The question is whether the tip hardness makes any difference, and in my opinion it does. If I hit a medium stroke shot with moderate low, I get more draw with a softer tip.

But, if some people can get more draw with soft tips than hard tips, while others can get more draw with hard tips than soft tips, that means that there's even more going on with the physics.

 

[BasementDweller]

I like how you think ineedaspot.

I think hard tips gloss over more often than soft tips do, which leads to more miscues. This can cause a player to have less confidence hitting the cue ball near the miscue limit with a hard tip. Then when the same player plays with a soft tip that is holding chalk really well they get more confidence and strike the ball lower.

I think this may be part of the reason why players often think the softer tip gives them more spin.

Or at least this player has falling into this trap.

 

[ineedaspot]

I like how you think ineedaspot.

I think hard tips gloss over more often than soft tips do, which leads to more miscues. This can cause a player to have less confidence hitting the cue ball near the miscue limit with a hard tip. Then when the same player plays with a soft tip that is holding chalk really well they get more confidence and strike the ball lower.

I think this may be part of the reason why players often think the softer tip gives them more spin.

Or at least this player has falling into this trap.

I think that's true also, but I don't think that's the full reason. the times I find the difference most noticeable are when I pick up a cue with a softer tip after I've been playing with my normal cue for a while. The first few shots I hit, I'm still hitting the way I would with the other cue, and on draw shots especially, it's like whoa, that ball came flying back more than I thought.

 

[macguy]

Although testing may render interesting information.
From my experience a hard tip draws more predictably. In other words if I was to draw the cue ball just a few inches or a few dozen inches, I can do it effortlessly and more accurately with a harder tip. Can I draw the cue ball three rails, probably but that is not my main concern playing the game.

I also like the feel when it contacts the cue ball and even the sound of a harder tip. No matter what tip it is, if the tip does not instill confidence it is not for you. If you feel like you are going to miss-cue all the time that is a problem.

 

[Tooler]

I like how you think ineedaspot.

I think hard tips gloss over more often than soft tips do, which leads to more miscues. This can cause a player to have less confidence hitting the cue ball near the miscue limit with a hard tip. Then when the same player plays with a soft tip that is holding chalk really well they get more confidence and strike the ball lower.

I think this may be part of the reason why players often think the softer tip gives them more spin.

Or at least this player has falling into this trap.

What about the guys that prefer masse as opposed to jumping. How can a harder tip get the same amount of spin on these softer stroked shots...? I know as far as my stoke goes, softer moves the ball easier, a lot easier.

 

[macguy]

What about the guys that prefer masse as opposed to jumping. How can a harder tip get the same amount of spin on these softer stroked shots...? I know as far as my stoke goes, softer moves the ball easier, a lot easier.

I have always felt that a harder tip causes a quicker reaction to the cue ball and a softer tip absorbed some of the reaction. I feel this make the harder tip better for small cue ball movements. I can feel what the cue ball is going to do and almost will it to do so with my stroke. Is it all in my head, maybe, but how you feel when you play is what counts for me..

 

[alphadog]

I like how you think ineedaspot.

I had to go back and read all the posts to see "why you need a spot" LOL

 

[dr_dave]

I recently got into a discussion about whether a soft tip actually results in more spin. The best pool physics resource I know of at colostate says that this is a myth:

http://billiards.colostate.edu/threads/cue_tip.html#hardness

I understand the physics of the argument, but I'm still not convinced. First of all, my personal experience says otherwise. If I hit the same shot, same stroke, I get noticeably more draw with a softer tip.

If everything was in fact the same in the comparison (same cue, same cue elevation, same stroke speed, same tip contact point, etc.), I would expect the hard tip to result in more draw because a hard tip usually creates a more efficient hit resulting in more CB speed for the given stroke which would result in more spin and less spin loss on the way to the OB.

Now, it is possible that a soft tip will allow a miscue limit farther out on the CB (as pointed out on the cue tip hardness resource page). If that is the case, then a soft tip could obviously allow more spin.

One way to think about problems like this is to do extreme thought experiments. As it happens, the colostate page links to an actual experiment where someone made a tip out of a rubber super ball. The results were much more english (and also much more deflection).
http://www.waynesthisandthat.com/billiards.htm#super tip

Obviously, a soft leather tip is not the same as a rubber tip, but the rubber experiment does show that, with some parameters, the instantaneous impulse model does indeed fall apart. So the question is, do whatever effects that occur with a rubber tip also occur with a soft leather tip to a lesser degree.

You may have missed the point of that rubber tip experiment. The purpose was to show that if you dramatically increases the tip contact time, the amount of squirt (AKA cue ball deflection) would increase dramatically, rendering the cue practically useless. Fortunately, the tip contact times for hard and soft leather tips are extremely small and similar (especially if compared to a rubber tip).

Regards,
Dave

 

[mikepage]

I recently got into a discussion about whether a soft tip actually results in more spin. The best pool physics resource I know of at colostate says that this is a myth:


[...]
The claim that hardness doesn't affect spin is based on a model that treats the contact between tip and ball as single instantaneous impulse, where tip hardness only affects the coefficient of restitution, and the duration of contact, but not the direction of the force applied.

The direction of the force is the direction of the stick. Yes there is a subtle sideways component; that is the force that causes squirt.

One key point to keep in mind is that it is the SAME FORCE that propels the ball and spins the ball. You can' t propose the direction of one change without the direction of the other changing.

The squirt force, as small as it is, reduces the amount of spin on the ball. A squirty stick striking a ball off center is equivalent to a hypothetical squirtless stick striking in a slightly different direction with LESS offset.

OK, this is a plausible model, and it is true that the tip and ball don't stay in contact for very long, but still, this isn't what actually happens. What actually happens is that the tip deforms (and the shaft bends slightly), and the force applied to the ball is primarily the result of the tip resisting this deformation and returning to its original shape.

OK

Like I said, modelling the contact as instantaneous might turn out to be accurate, but this is by no means obvious, at least not to me. The tip is a strangely-shaped thing, thicker in the middle than on the sides, and for an off-center hit, it doesn't deform straight back, it deforms a little bit sideways due to the friction and the fact that the ball surface is at an angle.

To really figure out what's going on would require a detailed computer model of the compression of the tip. This is a complicated thing, and it's not clear offhand what the results would be. For example, I'm not even certain that the force vector from the tip to the ball would point in roughly the same direction throughout the contact.

Again the best indicator of the direction of the force is the direction the cueball goes

[...]

I'd be interested what the other physics geeks here think about this topic. One thing that I would find convincing, or at least perplexing, would be some kind of controlled robot experiment showing that that tip consistency doesn't affect draw, at least not in the range of normal leather tips.

We actually HAVE discussed the effect of a changing force throughout the duration of tip-ball contact. A soft tip stays on the ball longer, and when you strike with a soft tip at an offset of, say 10mm, the tip stays on the ball while the ball begins to rotate--so that by the time the tip leaves the ball the offset might be at 12mm. If so, then the effective offset for the shot might be 11mm. And for a harder tip the effective offset might be slightly smaller.

But as far as the details of the compression providing a complex force that leads to more or less spin, it can only do that by also changing the direction the cueball moves. And we know from experience that doesn't happen,

 

[dr_dave]

The direction of the force is the direction of the stick. Yes there is a subtle sideways component; that is the force that causes squirt.

One key point to keep in mind is that it is the SAME FORCE that propels the ball and spins the ball. You can' t propose the direction of one change without the direction of the other changing.

The squirt force, as small as it is, reduces the amount of spin on the ball. A squirty stick striking a ball off center is equivalent to a hypothetical squirtless stick striking in a slightly different direction with LESS offset.

If people want more info on this effect, see getting more spin with an LD shaft.

Regards,
Dave

 

[macguy]

If everything was in fact the same in the comparison (same cue, same cue elevation, same stroke speed, same tip contact point, etc.), I would expect the hard tip to result in more draw because a hard tip usually creates a more efficient hit resulting in more CB speed for the given stroke which would result in more spin and less spin loss on the way to the OB.

Now, it is possible that a soft tip will allow a miscue limit farther out on the CB (as pointed out on the cue tip hardness resource page). If that is the case, then a soft tip could obviously allow more spin.


You may have missed the point of that rubber tip experiment. The purpose was to show that if you dramatically increases the tip contact time, the amount of squirt (AKA cue ball deflection) would increase dramatically, rendering the cue practically useless. Fortunately, the tip contact times for hard and soft leather tips are extremely small and similar (especially if compared to a rubber tip).

Regards,
Dave

What if the harder tip changes the extreme draw point. In other words you get the same draw without having to go to a limit where you may mis-cue. What tip provides the best reaction when just applied within the normal limits of applying english with the least effort and most predictable results.? Not extreme, but everyday shots we all play For me it is a harder tip..

 

[dr_dave]

If everything was in fact the same in the comparison (same cue, same cue elevation, same stroke speed, same tip contact point, etc.), I would expect the hard tip to result in more draw because a hard tip usually creates a more efficient hit resulting in more CB speed for the given stroke which would result in more spin and less spin loss on the way to the OB.

Now, it is possible that a soft tip will allow a miscue limit farther out on the CB (as pointed out on the cue tip hardness resource page). If that is the case, then a soft tip could obviously allow more spin.


You may have missed the point of that rubber tip experiment. The purpose was to show that if you dramatically increases the tip contact time, the amount of squirt (AKA cue ball deflection) would increase dramatically, rendering the cue practically useless. Fortunately, the tip contact times for hard and soft leather tips are extremely small and similar (especially if compared to a rubber tip).

Regards,
Dave

What if the harder tip changes the extreme draw point. In other words you get the same draw without having to go to a limit where you may mis-cue. What tip provides the best reaction when just applied within the normal limits of applying english with the least effort and most predictable results.? Not extreme, but everyday shots we all play For me it is a harder tip..

Per the 1st paragraph in my reply above, I agree with you ... a harder tip should result in more draw for a given effective tip offset from center.

Regards,
Dave

 

[fastone371]

I used to use soft tips (Kamui FWIW) but I did not like the way it made my cues feel like they were "dead". I also noticed that a brand new thick soft tip plays considerably different than an older thin worn down tip. One night I played a few racks with Orange Crush break cue that has a phenolic tip. I had no problem using draw, follow, and side spin, of course I was not using 2+ tips of spin, but more "normal" amounts of spin that you would normally use in competition. Once I learned that I could successfully move the cue ball around with a very hard tip, the phenolic tip, I switched to medium and hard tips on my player. I have not personally noticed any difference in the amount of spin that soft vs. hard tips deliver. I still have soft tips on a couple of other cues I use occasionally when practicing at home and do not notice any difference in the amount of spin I get with those compared to my hard tipped player, of course that is also on different cue and shaft combos so its not just a tip comparison. I am in the group that needs scientific proof that soft tips deliver more spin than hard tips, but almost anything is possible.

 

[Patrick Johnson]

If I hit the same shot, same stroke, I get noticeably more draw with a softer tip.

The difference is simply one of force - a harder tip transfers more force to the CB. More force doesn't matter with side spin because it adds to both RPMs and to CB speed without changing the spin-to-speed ratio - so more RPMs doesn't = more spin effect.

Draw is different because the CB is stopped by the OB, removing CB speed from the equation - so more RPMs = more draw.

In other words, you'd get the same result with a softer tip if you just hit a little harder.

pj
chgo

P.S. This is just a paraphrase of the excellent answers given by Mike Page and Dr. Dave above.

 

[mikepage]

Per the 1st paragraph in my reply above, I agree with you ... a harder tip should result in more draw for a given effective tip offset from center.

Regards,
Dave

I see what you are saying, but I think it is dangerous to talk about things other that whether [XXX] produces a greater spin-to-speed ratio.

Your harder tip gets more draw in the same way a heavier cue gets more draw for a given cue speed.

The danger I think of saying a
--harder tip gets more draw or a
--heavier cue gets more draw or that
--eating Wheaties for breakfast leads to more draw
is that some will think you're talking about spin-to-speed ratio

 

[ineedaspot]

If everything was in fact the same in the comparison (same cue, same cue elevation, same stroke speed, same tip contact point, etc.), I would expect the hard tip to result in more draw because a hard tip usually creates a more efficient hit resulting in more CB speed for the given stroke which would result in more spin and less spin loss on the way to the OB.

Yes, that would be the prediction of the "instantaneous impulse" model, which essentially assumes that the contact time is short enough that we can treat it as instantaneous, with the force vector pointing in the same direction the entire time.

Is this backed by experiment? The reason I ask is that this prediction is at odds with what I actually experience when changing from a harder to a softer tip -- I get noticeably more draw. And other people seem to have the same experience. So it seems to me that there may be something else going on with the tip-ball contact that is not captured by the instantaneous impulse model.

Now, it is possible that a soft tip will allow a miscue limit farther out on the CB (as pointed out on the cue tip hardness resource page). If that is the case, then a soft tip could obviously allow more spin.

This is true, but doesn't explain the effect that I am describing. I'm talking about a medium stroke, moderate draw shot, not something crazy pushing the miscue limit. In this situation I get more draw with a softer tip. Admittedly this is based on personal non-scientific observation. On the other hand, even though I'm an amateur, I play enough to be able to notice when I switch cues or tips, if I'm getting more action than before.

You may have missed the point of that rubber tip experiment. The purpose was to show that if you dramatically increases the tip contact time, the amount of squirt (AKA cue ball deflection) would increase dramatically, rendering the cue practically useless. Fortunately, the tip contact times for hard and soft leather tips are extremely small and similar (especially if compared to a rubber tip).

Yes, that may have been the original point of it, but the data drawn from it still relevant to the question of tip hardness versus amount of spin. It indicates, that at least in the extremes, tip consistency can affect the amount of spin. Moreover, given that I find that a softer leather tip yields more spin than a harder one, this is exactly what I would predict from an elastic rubber tip.

Another point, with the instantaneous impact model, the only additional variable that can enter the equation determining the amount of spin is contact time, by making effective contact point further out on the ball. I'm not sure that the super-ball-tip results are consistent with this (the soft-tip-yields-more-spin effect doesn't seem to be consistent with this either, but it's still possible that this effect is just my imagination).

For example, the description indicates "easily two to three times the amount of spin" which would imply the average contact point two to three times further out than the initial contact point, which seems like a lot. And the fact that chalking the rubber reduced the effect is also interesting, and seems to point to effects beyond the simply instantaneous-impulse-in-one-direction model.