clean vs dirty balls

[Patrick Johnson]

Why do freshly polished balls run significantly slower than dirty balls? Or is this my imagination?

I'm pretty sure it's your imagination unless you're talking about dirty cue balls with sidespin - they can pick up speed off the rails, especially when they rebound at shallow angles. But otherwise the speed of dirty balls is usually somewhat slower because they start out sliding before they gain forward roll and increased sliding friction slows them down when there's dirt on the balls or the cloth. However, I don't think rolling friction is increased much by dirty balls or cloth, so for instance if you hit a cue ball with follow (so it doesn't start out sliding) then it might not be slowed down by dirt (although it won't go faster or longer either).

pj
chgo

 

[Patrick Johnson]

The Saw:
Is this a theory Patrick or proven fact? Any high speed photography or other scientific proof to support?

Since this stuff is pretty simple physical interactions, I think the first question should be which explanation is best supported by simple common sense. I'd be interested to hear a common sense explanation for why dirty balls would "run faster".

As for high speed video of the effects I describe, there probably is some on Dr. Dave's website but he'd have to tell us where to find it. I don't know what other "scientific proof" you have in mind.

pj
chgo

 

[The Saw]

Since this stuff is pretty simple physical interactions, I think the first question should be which explanation is best supported by simple common sense. I'd be interested to hear a common sense explanation for why dirty balls would "run faster".

As for high speed video of the effects I describe, there probably is some on Dr. Dave's website but he'd have to tell us where to find it. I don't know what other "scientific proof" you have in mind.

pj
chgo

Could it be that when a dirty ball grabs the cloth/rail it has somewhat of a slingshot effect when it comes off? All I know is that I agree with Chris and Donnie that they come off the rail harder. I am going to go with the opinion of two of the best players in the country over that of armchair physics. My point is that, as usual, you are stating your suspected theory as a known fact. Prove your theory and I will accept it as fact.... Until then it is a theory and you should portray it as such, not as fact.....

 

[elvicash]

Dirty balls do not roll as far.

 

[PROG8R]

Are sweaty balls considered dirty balls?

 

[Robert Raiford]

And, btw, this hopping uses up some of the ball's energy so they might actually rebound at a slightly slower speed. Another reason that dirty balls rebound at a slower speed is because balls are generally sliding on the surface as they rebound and the extra friction from this will slow dirty balls down (until they begin rolling).

I don't think it's that simple. The hopping uses energy by converting follow to vertical motion, so it doesn't directly slow the ball down horizontally. In fact, there isn't contact with the cloth if they're airborne, so there's no rubbing against the cloth to slow down during that time. It would seem a dirty airborne ball leaves the cushion with a faster initial speed than a table-bound clean ball.

As I mentioned, the rebound velocity is slowed (besides cushion inefficiency) by sliding before rolling is achieved in the new direction. More follow is left on the cleaner ball in the direction of the cushion because less is rubbed off at contact. That means there is more 'braking' spin left to wear off (and slow down the ball) in the new direction after rebound.

While the dirty ball might slow down to a roll sooner if it's not airborne, the clean ball will ultimately have a slower initial rolling velocity because it has more braking spin to wear off (even though it will ultimately roll farther). Both balls convert spin to speed at the same 5:2 rate based on moment of inertia, and the cleaner one has more left to convert.

If you're going to talk about faster and slower, you have to say when That's why I tried to give reasons for the OP's perceptions of speed differences.

Robert

 

[Marop]

Donnie and Chris are correct. Dirty balls boing off the rails because they immediately start rolling due to the friction, clean or polished balls slide after contact with the rail before they pick up top spin. The slide effect is effectively killing the speed before the ball starts to roll.

You can test this this by taking a polished striped ball and rolling to the rail at medium to fast speed, you will be able to see the slide off the rail before the ball starts rolling. Due the same with a dirty striped ball and you will see that it immedately starts rolling in the direction of the rebound.

 

[jamesroberts]

I assume these guys don't mean that dirty balls rebound at a faster speed, because that's untrue. I assume they mean that dirty balls can "hop" when they rebound because the extra friction and their forward rotation makes them climb up on the cushion nose, lifting themselves off the surface (this is true). Even relatively clean balls can hop if the cushion cloth is sticky or if the nose height is too low. And, btw, this hopping uses up some of the ball's energy so they might actually rebound at a slightly slower speed. Another reason that dirty balls rebound at a slower speed is because balls are generally sliding on the surface as they rebound and the extra friction from this will slow dirty balls down (until they begin rolling).

pj
chgo

no they mean dirty balls rebound at a faster speed, or gives the appearance that way, i wonder if it has something to do with relative humidity

I was playing last night with dirty balls for about 2 hours and struggling, the owner cleaned the balls and the table stopped playing bouncy , i could control my cue ball and i started winning

 

[The Saw]

I don't think it's that simple. The hopping uses energy by converting follow to vertical motion, so it doesn't directly slow the ball down horizontally. In fact, there isn't contact with the cloth if they're airborne, so there's no rubbing against the cloth to slow down during that time. It would seem a dirty airborne ball leaves the cushion with a faster initial speed than a table-bound clean ball.

As I mentioned, the rebound velocity is slowed (besides cushion inefficiency) by sliding before rolling is achieved in the new direction. More follow is left on the cleaner ball in the direction of the cushion because less is rubbed off at contact. That means there is more 'braking' spin left to wear off (and slow down the ball) in the new direction after rebound.

While the dirty ball might slow down to a roll sooner if it's not airborne, the clean ball will ultimately have a slower initial rolling velocity because it has more braking spin to wear off (even though it will ultimately roll farther). Both balls convert spin to speed at the same 5:2 rate based on moment of inertia, and the cleaner one has more left to convert.

If you're going to talk about faster and slower, you have to say when That's why I tried to give reasons for the OP's perceptions of speed differences.

Robert

Rep to you! Great post!

 

[Jal]

...I am going to go with the opinion of two of the best players in the country over that of armchair physics. My point is that, as usual, you are stating your suspected theory as a known fact. Prove your theory and I will accept it as fact.... Until then it is a theory and you should portray it as such, not as fact.....

Saw,

I think this is a completely unfair description of his contributions. He doesn't have a background in math or physics, I do, yet he's helped me correct fuzzy or outright erroneous ideas. You're doing yourself a disservice if you dismiss his "armchair physics."

For what it's worth, I think R. Raiford gave the best overall description, particularly of the topspin effects. But unless I missed it, Turtle hasn't specified the circumstances in which the balls are acting slower. Is it cushion rebounds?

If I had a set of balls to polish (alright ), I'd probably try a slurry of powdered rottenstone and water, which is used to rub furniture finishes to a high gloss. It's cheap, and the last time I looked, was readily available (Ace hardware). The manufacture of the compounds used on my buffer wheels, which are in a wax or grease matrix, recommends final cleaning with powdered whiting (calcium carbonate), also readily available in paint stores the last time I tried. Just a thought.

Jim

 

[Bob Jewett]

Why do freshly polished balls run significantly slower than dirty balls? Or is this my imagination? Those dirty balls run so fast. Anyone, please clarify.

Thanks in advance for your reponses

Hmmm...

If the rail-ball contact is slippery, the ball can lose a lot of speed coming off the cushion as Robert Raiford explained. This is most commonly seen on brand new cloth when banking a stripe (or using a measles cue ball). You can also get the effect by waxing a ball. I have seen the opposite effect when the rail was very sticky, and I could get the cue ball to go six table lengths without much effort.

I think the sliding bed-ball contact being slippery or sticky has little effect on the distance the ball goes (but it greatly affects how well the cue ball keeps draw over a distance).

If you want to measure the speed of your cloth, it can be done as Robert Raiford mentioned above: Measure the time a ball takes for the last leg of a good lag shot that doesn't quite touch the last cushion. Square the time and multiply by 2. This will give you a "speed" number near 100. A higher number means "faster" cloth. If you take 1 over the number it will give you the equivalent up-hill slope that the cloth provides to a rolling ball. For example, a cloth speed of 100 is the equivalent of a 1% slope. I have seen cloth as fast as 200. See http://www.sfbilliards.com/articles/1995-04.pdf for some more info.

 

[sfleinen]

BallStar vs. Diamond Pro ball polisher?

Well I have known a few good ball cleaners in my day.
I can check and see any of them are still available. Dont hold your breath though they tend to go fast.

On a serious note.
By a BallStar. Run you about $450.00.
I have one. Nice unit. Cheap enough.

http://www.pooldawg.com/product/ballstar-pool-and-billiards-ball-cleaner?source=trafficleader

http://www.billiards.com/ball-cleaners/automatic-ball-cleaner-polisher

Hey Sev:

Does this BallStar unit spin the balls against a cylindrical wall of carpet, instead of vibrating them? If so, it appears to be a less expensive version of the Diamond Pro ball polisher:

http://diamondbilliards.com/Accessories/DiamondProBallPolisher/tabid/77/Default.aspx

(Although the price shown for Diamond's product is for the dual 8 ball platter version -- cleans the whole ball set in one fell swoop. So perhaps Diamond's single platter version might be equal in price to the BallStar?)

Thoughts?
-Sean

 

[Patrick Johnson]

Robert Raiford:
I don't think it's that simple.

I don't either - I was just too busy and lazy to get into it.

The hopping uses energy by converting follow to vertical motion, so it doesn't directly slow the ball down horizontally. In fact, there isn't contact with the cloth if they're airborne, so there's no rubbing against the cloth to slow down during that time. It would seem a dirty airborne ball leaves the cushion with a faster initial speed than a table-bound clean ball.

I'm not so sure - I'd guess that as the ball climbs up the cushion nose and the cushion uncompresses some of the cushion's horizontal rebound force spins the ball rather than pushing it, reducing the ball's horizontal velocity and replacing some (or all?) of the braking spin that was lost.

I'd also guess that the extra momentary friction created by the ball landing on the surface makes a difference.

I think your analysis makes perfect sense (as usual), but I also think there's even more to consider that might work against your general conclusion. I'm thinking there's probably very little difference either way in the overall outcome, but I'm willing to be persuaded otherwise by tests. I've done some simple ramp tests myself at slower speeds (not enough to create a significant hop off the rail) and cleaner balls always seem to travel a little farther. Maybe this changes with more of a hop, but I'm inclined to doubt it.

One possible alternate explanation for the perception that dirty balls rebound farther is that we might tend to hit them harder.

As Saw said, great post.

pj
chgo

 

[Patrick Johnson]

they mean dirty balls rebound at a faster speed

Maybe they do, but "boing" and "bounce harder" might also mean they simply hop more (which they do).

pj
chgo

 

[donny mills]

I assume these guys don't mean that dirty balls rebound at a faster speed, because that's untrue. I assume they mean that dirty balls can "hop" when they rebound because the extra friction and their forward rotation makes them climb up on the cushion nose, lifting themselves off the surface (this is true). Even relatively clean balls can hop if the cushion cloth is sticky or if the nose height is too low. And, btw, this hopping uses up some of the ball's energy so they might actually rebound at a slightly slower speed. Another reason that dirty balls rebound at a slower speed is because balls are generally sliding on the surface as they rebound and the extra friction from this will slow dirty balls down (until they begin rolling).

pj
chgo

No I mean dirty balls come off the rail faster than freshly polished balls... matter of fact quite a bit faster and they come off shorter also... and no they didn't hop.
I would say we can bet on this but you'll probably try it and see that it's true.

 

[donny mills]

Dirty balls do not roll as far.

If they hit a rail they roll farther.

 

[TURTLE]

Clean vs dirty balls

Thanks for the clarifications. I'm glad it's not just my imagination. What I experienced which was responsible for my initial question "DIRTY BALLS RUN FASTER" was the result of using follow with a dirty ball ( or itchy ball, or sweaty ball to some of you..lol ) hitting against the head rail. The added amount of action and distanced I received with a dirty ball vs a clean ball was tremendous. With a polished ball, no matter how much I stroked the follow, the cue ball could not achieve close to the same distanced received with the dirty ball. And yes, yes, the dirty cue ball definetely really bounced off the rail pretty hard.

ty

 

[Sev]

Hey Sev:

Does this BallStar unit spin the balls against a cylindrical wall of carpet, instead of vibrating them? If so, it appears to be a less expensive version of the Diamond Pro ball polisher:

http://diamondbilliards.com/Accessories/DiamondProBallPolisher/tabid/77/Default.aspx

(Although the price shown for Diamond's product is for the dual 8 ball platter version -- cleans the whole ball set in one fell swoop. So perhaps Diamond's single platter version might be equal in price to the BallStar?)

Thoughts?
-Sean

The Ballstar is a single carpet. Probably equivalent price. By the looks of the Diamond Jim I would not be surprised if it came out of the same plant as the BallStar. I could be wrong on that though.

 

[Robert Raiford]

I was just too busy and lazy to get into it.

Since when?

I'm not so sure - I'd guess that as the ball climbs up the cushion nose and the cushion uncompresses some of the cushion's horizontal rebound force spins the ball rather than pushing it, reducing the ball's horizontal velocity and replacing some (or all?) of the braking spin that was lost.

Interesting idea, but I think it could still work in 'my' favor (assuming the effect is there at all.) Since the rail is above the ball's center, as the ball rose, the cushion would likely give an impulse closer to its center than if it stayed on the table. I can't remember if the Jacksonville guys did any profile ball-rail shots where there was significant jumping at the cushion, but it would be neat to explore more cushion interactions next time around.

I'd also guess that the extra momentary friction created by the ball landing on the surface makes a difference.

That might cause the ball to slow down faster while it's touching the table as the frictional force increases proportionally with the addition downward force from the fall, but since it would likely bounce more than once as it settled, the additional airtime would be countering the effect.

More interestingly related to this is the fact that its final rolling velocity would in no way be affected by the fluctuations in the frictional force from the bouncing. The coefficient of friction could change any which way along the balls path, which would have the same effect as the bouncing (i.e. change how long it took to slow down), but the ball would still slow down to the same initial rolling speed. That's because what matters is the proportional tradeoff between spin and speed, and that's decided by the ball's moment of inertia, not the particular nature of the frictional force on the table (a very counterintuitive result.)

One possible alternate explanation for the perception that dirty balls rebound farther is that we might tend to hit them harder.

That's exactly why I mentioned Bob Jewett's table speed measurement. A 'faster' table means it takes you longer to travel the same distance to a stop, so you must have hit the 'faster' shot slower. In pool, we're trying to stop the cue ball at a certain place for position, so we shoot slower on faster equipment to achieve the same results (or use less spin, or both).

Robert

 

[donny mills]

Thanks for the clarifications. I'm glad it's not just my imagination. What I experienced which was responsible for my initial question "DIRTY BALLS RUN FASTER" was the result of using follow with a dirty ball ( or itchy ball, or sweaty ball to some of you..lol ) hitting against the head rail. The added amount of action and distanced I received with a dirty ball vs a clean ball was tremendous. With a polished ball, no matter how much I stroked the follow, the cue ball could not achieve close to the same distanced received with the dirty ball. And yes, yes, the dirty cue ball definetely really bounced off the rail pretty hard.

ty

Kind of ironic that your name is turtle and we're talking about wax on the balls and stuff... Turtle/ turtle wax... hmmm.