Nappy cloth = incredible draw?

[spoons]

Has this discussion happened on here, yet?

I've noticed a few different places that I've played with nappy cloth, that it seems overly easy to draw the ball - and consequently, very difficult to draw the ball with any amount of control. I would think it should be the other way around with the nap providing more friction, and killing the backspin.

Apart from a light cue ball, what would be the reason for that?

Thanks!

 

[NewStroke]

Dr Dave will probably correct me but I think the additional friction allows the cue ball to catch "harder" producing more back spin. I would also guess the cue ball does not spin very long before drawing back like it would on Simonis or equivalent cloth.

Now my brain hurts from actually thinking about science. THANKS!

 

[jsp]

Has this discussion happened on here, yet?

I've noticed a few different places that I've played with nappy cloth, that it seems overly easy to draw the ball - and consequently, very difficult to draw the ball with any amount of control. I would think it should be the other way around with the nap providing more friction, and killing the backspin.

Apart from a light cue ball, what would be the reason for that?

Thanks!

The higher friction of the nap cloth (compared to worsted cloth) allows the draw spin on the CB to "take", or grab the cloth, better after contacting the OB. This allows the CB to convert more of its rotational energy into translational energy without losing much of its energy due to slippage between CB and cloth. Keep in mind that the more slippage that occurs between the CB and cloth, the more energy you lose due to friction (heat) and the less you convert to translation energy.

But also keep in mind that the higher cloth friction of nap cloth also makes the CB lose more of its energy as the CB approaches the OB. So for shots where the CB and OB are fairly close together, drawing the CB may be easier. But for shots where the CB and OB are farther apart, the opposite may be true.

 

[Patrick Johnson]

I think the additional friction allows the cue ball to catch "harder" producing more back spin. I would also guess the cue ball does not spin very long before drawing back like it would on Simonis or equivalent cloth.

Dr. Dave may correct both of us, but I think the key is how much backspin the CB has on it when it hits the OB. Nappier cloth normally rubs off more CB spin before CB/OB contact, so there will be less draw distance. In other words, slipperier cloth draws farther/easier.

If you set up the same shot on two tables (one with smooth Simonis and the other with nappy cloth), and can get the CB to hit the OB with the same amount of backspin on both tables (you'll have to hit lower or harder on the nappier cloth), it will "peel out" for a longer time on the Simonis and for a shorter time on the nappy cloth but will draw back just about the same distance on both.

pj
chgo

EDIT: P.S. However, I've seen some nappy cloth that's very slippery.

 

[cuesmith]

Dr. Dave may correct both of us, but I think the key is how much backspin the CB has on it when it hits the OB. Nappier cloth normally rubs off more CB spin before CB/OB contact, so there will be less draw distance. In other words, slipperier cloth draws farther/easier.

If you set up the same shot on two tables (one with smooth Simonis and the other with nappy cloth), and can get the CB to hit the OB with the same amount of backspin on both tables (you'll have to hit lower or harder on the nappier cloth), it will "peel out" for a longer time on the Simonis and for a shorter time on the nappy cloth but will draw back just about the same distance on both.

pj
chgo

EDIT: P.S. However, I've seen some nappy cloth that's very slippery.

From my experience, the big factor is how new the nappy cloth is. When it's fresh, it still has the surface chemicals used in the manufacturing process, probably a silicon of some kind, which makes the balls slide a lot. This is when the super draw shots are possible. When the cloth gets old and dirty, things change dramatically! It's the same with worsted cloth, just not as obvious.


just more hot air!


Sherm

 

[jsp]

If you set up the same shot on two tables (one with smooth Simonis and the other with nappy cloth), and can get the CB to hit the OB with the same amount of backspin on both tables (you'll have to hit lower or harder on the nappier cloth), it will "peel out" for a longer time on the Simonis and for a shorter time on the nappy cloth but will draw back just about the same distance on both.

What complicates your analysis is that there are two factors that affect the drawing distance. One is the difference in friction between the two cloths, as we've already discussed. But the other is the difference in elasticity (not sure if that's the correct term to use here), or the difference in hardness/softness, between the surfaces. Slippage mainly deals with the former, but once the CB already achieves natural role the latter is the dominant factor.

Now, assuming that the "hardness/softness" between nap and worsted cloths is the same, then your experiment would definitely show that the nap cloth will have the larger drawing distance (assuming the same amount of backspin after contacting the OB). But the nap cloth is definitely "softer" than the worsted cloth, which would inhibit the rolling distance more. So it's hard to say which factor (friction or softness) wins out. In some cases the nap cloth would draw more, and in some cases the worsted cloth. It depends on the exact type and condition of the cloths used, and the amount of backspin. You may end up being correct after all that in most cases both will draw back about the same distance.

 

[Jal]

The higher friction of the nap cloth (compared to worsted cloth) allows the draw spin on the CB to "take", or grab the cloth, better after contacting the OB. This allows the CB to convert more of its rotational energy into translational energy without losing much of its energy due to slippage between CB and cloth. Keep in mind that the more slippage that occurs between the CB and cloth, the more energy you lose due to friction (heat) and the less you convert to translation energy.

Jsp,

Nevertheless, given the same amount of retained backspin after OB impact, the speed of the cueball when it reaches natural roll is independent of the amount of cloth friction. Ignoring any slight corrections for air drag, inelastic CB-OB collision, etc., its speed at the moment it attains natural roll is 2/7'ths of its relative surface speed (RW) immediately after impact. All else equal, a slicker cloth with then produce a slightly longer draw distance because the cueball has to travel farther (backward) before the onset of roll.

But also keep in mind that the higher cloth friction of nap cloth also makes the CB lose more of its energy as the CB approaches the OB. So for shots where the CB and OB are fairly close together, drawing the CB may be easier. But for shots where the CB and OB are farther apart, the opposite may be true.

As far as sliding friction goes, it surely is easier to get the same draw distance on slicker cloth at large CB-OB separations.

Jim

 

[Destrukkt]

I wish my normal felt would allow me to put english on the ball.

Only time I can is on simmonis or champion felt at my local pool halls.

 

[Bob Jewett]

Has this discussion happened on here, yet?

I've noticed a few different places that I've played with nappy cloth, that it seems overly easy to draw the ball - and consequently, very difficult to draw the ball with any amount of control. I would think it should be the other way around with the nap providing more friction, and killing the backspin.

Apart from a light cue ball, what would be the reason for that?

Thanks!

I've played on nappy cloth that was both slow and easy to draw on. I think it was high-nylon content and therefore slippery, but was thick/nappy so that the ball slowed down quickly after it got going. The light cue ball is most often the culprit, though. Try drawing one object ball off another, say the 15 and 14.

 

[Donny Wessels]

how tight the cloth is pulled will make a huge difference. Although I never tried it myself but I heard if the cloth is installed upside down the cloth will play slower but will have more bite.

 

[jsp]

Nevertheless, given the same amount of retained backspin after OB impact, the speed of the cueball when it reaches natural roll is independent of the amount of cloth friction. Ignoring any slight corrections for air drag, inelastic CB-OB collision, etc., its speed at the moment it attains natural roll is 2/7'ths of its relative surface speed (RW) immediately after impact.

Help me out Jal, because I just don't see it. Taking it to both extremes, I can certainly imagine the CB drawing further back on a rubber surface compared to a sheet of ice (assuming the same amount of retained backspin after OB impact).

For the sheet of ice case, much of the spin has to be lost or dissipated before the CB surface speed is reduced enough for static friction to take hold such that the CB achieves natural roll. Obviously in the zero friction case, the CB would just spin in the same spot forever. So how exactly can you say that the speed of the CB when it reaches natural roll is independent of the amount of cloth friction?

 

[Jal]

Help me out Jal, because I just don't see it. Taking it to both extremes, I can certainly imagine the CB drawing further back on a rubber surface compared to a sheet of ice (assuming the same amount of retained backspin after OB impact).

Jsp,

Actually, I remember Mike Page once made some sort of a wager as to how far a ball might be drawn on level ice. The general argument goes like this. Assuming the cueball comes to essentially a complete stop (full hit), and has a spin of W (radians/sec), initially the bottom of the ball is moving over the surface at a speed of R*W (radius X spin rate). Sliding friction at the surface produces a force and a torque, the latter being equal to R*F, and both act until natural roll takes over. The force propels the cueball as a whole, while the torque reduces its spin. This takes place until its acquired speed equals and therefore exactly cancels the spin component of surface speed (V'=R*W', which is natural roll, by definition).

The relevant point is that the ratio of force to torque is fixed when a force (friction at the surface in this case) acts at a fixed distance from the center of a sphere. Therefore, a ball always acquires a certain increment of speed for every unit of spin it loses to friction. This continues until they "meet" (V'=R*W' ). The moment of inertia of a sphere (= (2/5)*M*R^2) dictates that this will occur when V'=(2/7)*R*W, where W was its initial spin rate immediately after OB impact. All of this is independent of how fast it reaches natural roll, i.e., whether it happens on a slick cloth or a sticky one (or ice), due to the fixed ratio of force to torque. Once natural roll takes over, rolling resistance comes into play, which is a different dynamic as you point out.

The longer (time-wise) it takes to reach natural roll, the more distance a ball will have traveled up to that point. That's because its time averaged speed is the same in any case (V'/2), and the distance traveled is (V'/2)*T, where T is the time it took to reach the rolling state. So even though a more "grabby" surface would seem to have the edge, you will nevertheless see more total draw distance with a slicker one, all else equal (e.g., rolling resistance). In the case of ice, which has a very small rolling resistance to boot, you should be able to draw much farther than on rubber, assuming the friction doesn't generate enough heat such that the cueball digs itself into a pit.

Does that make any sense?

Jim

 

[Patrick Johnson]

JAL:
All else equal, a slicker cloth with then produce a slightly longer draw distance because the cueball has to travel farther (backward) before the onset of roll.

Of course it takes more time for the CB to achieve roll on slicker cloth, but during that extra time it's traveling less distance per revolution. Does it really travel farther before achieving roll, or do you mean after? Sorry, I can't follow your technical explanation...

pj
chgo

 

[Patrick Johnson]

What complicates your analysis is that there are two factors that affect the drawing distance. One is the difference in friction between the two cloths, as we've already discussed. But the other is the difference in elasticity (not sure if that's the correct term to use here), or the difference in hardness/softness, between the surfaces. Slippage mainly deals with the former, but once the CB already achieves natural role the latter is the dominant factor.

Yes, that seems like it should be a factor. But if both you and JAL are right, then the CB travels farther on slick cloth both before and after achieving roll, which would compound the difference. That seems like too much difference to me - I only know what I've heard from people like Bob Jewett, Mike Page and Ron Shepard, but I believe they've said the total draw distance is similar on both kinds of cloth assuming equal RPMs at contact.

I could be wrong - I remember once many years ago...

pj
chgo

 

[Bob Jewett]

... but I believe they've said the total draw distance is similar on both kinds of cloth assuming equal RPMs at contact. ...

Draw distance is determined by the RPMs (which determines the total energy in the backspin) and the speed of the cloth, with very slight influence from the stickiness of the cloth. Cloth can theoretically have all four pairs of sliding/rolling frictions: sticky/fast sticky/slow slippery/fast slippery/slow. You might find these in:

New Simonis -- slippery/fast (extreme = ice)
High-nylon nappy -- slippery/slow (or wax the cue ball)
Bar table w/beer and crumbs -- sticky/slow
??? sticky/fast (like hard rubber)

 

[spoons]

So if I'm understanding this correctly: a clean, nappy cloth or a nappy cloth made out of a slicker material such as nylon, might actually have a lesser effect on cue ball backspin than than say a dirty, worsted cloth. And, all other things being equal, on those slicker surfaces, the cue ball should reach the object ball with more spin. Right?

I understand that the cloth will also affect the behavior of the ball once it begins to draw back, but this certainly sounds like a reasonable explanation for my original question.

It also fits with what I know about the tables in question. The felt does seem to be very slick. This place also keeps the equipment fairly clean, and I sometimes get the feeling I might be the only one who's ever used a piece of chalk while playing there. So it sounds like that would compound the effect.

Thanks everyone! And please continue the physics discussion. Even though most of the details are over my head, I like to geek out on reading this stuff!

 

[Jal]

Of course it takes more time for the CB to achieve roll on slicker cloth, but during that extra time it's traveling less distance per revolution. Does it really travel farther before achieving roll, or do you mean after? Sorry, I can't follow your technical explanation...

pj
chgo

Patrick,

Yes it does travel farther before reaching natural roll, but it's not all that obvious why. Imagine that the friction force is constant as the cueball goes from zero up to natural roll speed. (This isn't a necessary assumption, and isn't exactly true, particularly right after impact (bounce), but it's very nearly true and simplifies things.) If you plotted the cueball's ever increasing speed against time, it would be a straight line sloping upwards. Let's say at time T it reaches natural roll at speed V'. So how far did it travel?

I think it's somewhat obvious, although you might require a more rigorous argument to be convinced, that its average speed over this period is V'/2. It's V'/2 because it went from zero to V' in a linear fashion. Call it Vav. The distance traveled, D, during a time T, by anything, no matter how complicated its speed might vary over time, is Vav*T (the asterisk denotes simple multiplication). Since Vav=V'/2, and since the natural roll speed V' is independent of the magnitude of cloth friction (i.e., it doesn't matter how quickly it achieves natural roll given the same initial spin), Vav is also independent of this. And since D=Vav*T, the distance D depends only on T, and is greater as T is longer.

Sorry if I've made things worse, but it's not all that easy (for me) to provide a more straightforward argument when you have a continuously varying speed. That's why calculus was invented, although it isn't too much of a leap to go there (mainly, divide the time interval into very small increments of dt and add up all the contributions of Vdt as V varies with t). Maybe someone (smarter) can conjure up a more intuitive description if the above doesn't persuade.

Another way of looking at it is to consider the distance if the speed was absolutely constant throughout and equal to V' right from the start. The plot would have speed as a straight line parallel to the time axis at height V'. The distance traveled would be V'*T. This is the "area" under a rectangle with sides of length V' and T. "Area" doesn't mean a spacial area in the normal sense, of course, but a abstract representation of the distance as such. When the speed ramps up linearly to V', we have a triangle instead of a rectangle,. The area of the triangle is (1/2)V'*T as with any triangle (1/2 base X height). If you accept this "area" as a legitimate representation of distance traveled, and that V' only depends on the retained spin after CB-OB impact, you reach the same conclusion.

Not sure if any of that helps, but I'm honestly not trying to obscure with the damned math. Once you're comfortable with it, it tells you things that are sometimes very hard or impossible to see otherwise.

Jim

 

[Patrick Johnson]

Patrick,

Yes it does travel farther before reaching natural roll, but it's not all that obvious why. Imagine that the friction force is constant as the cueball goes from zero up to natural roll speed. (This isn't a necessary assumption, and isn't exactly true, particularly right after impact (bounce), but it's very nearly true and simplifies things.) If you plotted the cueball's ever increasing speed against time, it would be a straight line sloping upwards. Let's say at time T it reaches natural roll at speed V'. So how far did it travel?

I think it's somewhat obvious, although you might require a more rigorous argument to be convinced, that its average speed over this period is V'/2. It's V'/2 because it went from zero to V' in a linear fashion. Call it Vav. The distance traveled, D, during a time T, by anything, no matter how complicated its speed might vary over time, is Vav*T (the asterisk denotes simple multiplication). Since Vav=V'/2, and since the natural roll speed V' is independent of the magnitude of cloth friction (i.e., it doesn't matter how quickly it achieves natural roll given the same initial spin), Vav is also independent of this. And since D=Vav*T, the distance D depends only on T, and is greater as T is longer.

Sorry if I've made things worse, but it's not all that easy (for me) to provide a more straightforward argument when you have a continuously varying speed. That's why calculus was invented, although it isn't too much of a leap to go there (mainly, divide the time interval into very small increments of dt and add up all the contributions of Vdt as V varies with t). Maybe someone (smarter) can conjure up a more intuitive description if the above doesn't persuade.

Another way of looking at it is to consider the distance if the speed was absolutely constant throughout and equal to V' right from the start. The plot would have speed as a straight line parallel to the time axis at height V'. The distance traveled would be V'*T. This is the "area" under a rectangle with sides of length V' and T. "Area" doesn't mean a spacial area in the normal sense, of course, but a abstract representation of the distance as such. When the speed ramps up linearly to V', we have a triangle instead of a rectangle,. The area of the triangle is (1/2)V'*T as with any triangle (1/2 base X height). If you accept this "area" as a legitimate representation of distance traveled, and that V' only depends on the retained spin after CB-OB impact, you reach the same conclusion.

Not sure if any of that helps, but I'm honestly not trying to obscure with the damned math. Once you're comfortable with it, it tells you things that are sometimes very hard or impossible to see otherwise.

Jim

So, to summarize:

1. Cloth has both "sliding resistance" (slick vs. sticky) and "rolling resistance" (smooth vs. nappy), and both independently affect how far the CB will draw. Sliding resistance and rolling resistance can be present in different combinations: smooth/slick, smooth/sticky, nappy/slick, nappy/sticky. Sliding resistance affects the CB before and after contact (while it's skidding); rolling resistance affects the CB only after contact (while it's rolling).

2. For the same tip height and speed, the CB will reach the OB with more backspin on slick cloth, and will draw farther.

3. If the CB reaches the OB with the same backspin (because it's hit differently or from a different distance), it will draw farther on slick cloth before achieving roll and will roll farther on smooth cloth after achieving roll. Therefore, maximum draw is achieved on cloth that is both slick and smooth.

Does that cover it?

pj
chgo

 

[Andrew Manning]

Therefore, a ball always acquires a certain increment of speed for every unit of spin it loses to friction. This continues until they "meet".

Isn't this ignoring dissipated energy? Any heat produced by the friction is energy from the backspin that will not contribute to draw distance. Any "wear" of the cloth or the ball also uses energy from the rotational energy of the ball, which is therefore unavailable to contribute to draw. I don't think these are negligible, and I don't think they're equal on different types of surface.

-Andrew

 

[Ball Banger]

how tight the cloth is pulled will make a huge difference. Although I never tried it myself but I heard if the cloth is installed upside down the cloth will play slower but will have more bite.

SD

Cloth tension is a big factor on both draw and follow shots. But you hit a real sore spot with about a local vendor who has his kid do the recovering. Typical of Kids attitudes these days he could care less. There is no uniform tension on the cloth from one end to the other.

BTW I remember very first shot I ever made on Simonis cloth with a light CB. What was intended as a table length stop shot ended up as a Table length draw. I had been playing with a mud ball on the old wool cloth.