Physics Questions on "sliding" as it relate to pool balls.

I say the cue ball will slide one way or the other on all shots untill the friction of the cloth takes over and the ball rolls forward natrually even on a soft hit, the impact of the hit pushes the cue ball off the resting position slightly before turning. The key is to recognize slide when cue ball is not spinning. I say there are spin induced slide,collision induced slide, and diretional slide like we use on a stop shot. I use what i called directional slide as a reference to calculate control of cue ball after contact. The other types of slide i do not know how to use consciencely to my advantage. I been thinking about this all night my head hurts thanks alot. I know i must be wrong to a point this. But that is all i could come up with.
 
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Comments from the bottom of the heap:

Every ball collision results in some degree of skid.

A ball can, and frequently is, rolling and sliding at the same time.

I hold these truths to be self evident.

Dave Nelson
 
Drew said:
Um...skid is very real. It's what happens when the friction between cb and ob cause the two balls to momentarily stick together...guess what happens if you're cutting a ball and they unexpectedly stick together briefly? That's right, you'll miss the ball.
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extra fun part to this (and related to my question i'll ask in a sec) is when you have English on the cue and this happens, you can impart some amount of English to the object ball. Or even if you have draw on the cue impart follow to the object ball. I haven't been able to visually prove to myself yet that with follow on the cue you can get draw on the object though.
 
for the people with the really good answer :) here is a follow up question of my own...


is the ball sliding the whole time even if shot at table speed with tip hitting vertical center of ball but 1 tip off to left or right imparting English? my head says its sliding the entire time in that case, with only a hair of the spin translating into movement - swerve.
 
EasyEJL said:
for the people with the really good answer :) here is a follow up question of my own...


is the ball sliding the whole time even if shot at table speed with tip hitting vertical center of ball but 1 tip off to left or right imparting English? my head says its sliding the entire time in that case, with only a hair of the spin translating into movement - swerve.
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Like all sidespin shots it stops sliding/curving at different distances depending on how hard it's hit..

pj
chgo
 
Patrick Johnson said:
Like all sidespin shots it stops sliding/curving at different distances depending on how hard it's hit..

pj
chgo
Click to expand...

Maybe more of the question is "isn't the ball sliding always if it still spinning?". For example in effect isn't the ball sliding if its lost all forwards momentum but is still spinning?
 
EasyEJL said:
for the people with the really good answer :) here is a follow up question of my own...


is the ball sliding the whole time even if shot at table speed with tip hitting vertical center of ball but 1 tip off to left or right imparting English? my head says its sliding the entire time in that case, with only a hair of the spin translating into movement - swerve.
Click to expand...
If you hit with a completely level stick -- this is usually impossible -- the cue ball will not curve with side spin.

If you hit normally with just side spin, the cue ball will curve due to the combination of spin and slight elevation. The curve will stop when the cue ball is rolling smoothly on the cloth.

It is a little tricky to understand that the cue ball can be both spinning with side spin and rolling smoothly on the cloth. The best visualization helper I've seen is from Ron Shepard: Imagine a barrel like a 55-gallon cylindrical drum. Tilt it to the side about 20 degrees and start rolling it forward. It is both spinning and rolling smoothly on the ground. A pool ball can do the same thing.
 
EasyEJL said:
for the people with the really good answer :) here is a follow up question of my own...


is the ball sliding the whole time even if shot at table speed with tip hitting vertical center of ball but 1 tip off to left or right imparting English? my head says its sliding the entire time in that case, with only a hair of the spin translating into movement - swerve.
Click to expand...
A CB struck off center slides only until forward roll develops (which happens very soon for above-center hits) and during swerve (which happens over a very short distance for slow speed shots). After slide and swerve, the CB rolls with sidespin in a straight line with no slip whatsoever. For more information and video demonstrations, see:

Enjoy,
Dave
 
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dr_dave said:
A CB struck off center slides only until forward roll develops (which very soon for above-center hits) and during swerve (which happens over a very short distance for slow speed shots). After slide and swerve, the CB rolls with sidespin in a straight line with no slip whatsoever. For more information and video demonstrations, see:

Enjoy,
Dave
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Hi Dave,

Do you mean that a ball rolling an a diagonal axis rolls in a straight line and does not gradually stray off of that straight line.

Also, it seems to me that there is a different meaning to many as to just what is meant by 'side spin'. To me, & apparently to others, anything not on the exact verticle axis is a form of side spin while it seesm that the 'science' community seem to consider a ball spinning only on the horizontal axis a 'side spin'. I'm not referring to just this thread but in general. Maybe a clarification 'thread' is in order. If I missed it, please excuse me & forget it.

Best Regards,
 
Exactly...

dr_dave said:
A CB struck off center slides only until forward roll develops (which very soon for above-center hits) and during swerve (which happens over a very short distance for slow speed shots). After slide and swerve, the CB rolls with sidespin in a straight line with no slip whatsoever. For more information and video demonstrations, see:

Enjoy,
Dave
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I was going to post the same answer pretty much.

My original answer pretty much answers this question. So long as the spin is not in line or opposite to the directional velocity, it will have no effect on whether or not the ball is sliding or rolling.

So the short answer is no, only side spin, where swerve is not a factor, will have no affect on slide versus roll.

Jaden

p.s. As Dave said, with a perfectly level cue...This is why when I teach people BHE, I teach them to elevate and lower their bridge hand for follow and draw to minimize swerve. A lot of people who first try BHE, try to keep a center ball bridge all the time and rotate with their back hand for follow and draw as well.

That's why many people think that BHE is VERY limited... When you lower and elevate your bridge hand for follow and draw, it minimizes swerve and limits its' effect on the shot making BHE more accurate in more circumstances without adjustment.
 
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Bob Jewett said:
If you hit with a completely level stick -- this is usually impossible -- the cue ball will not curve with side spin.

If you hit normally with just side spin, the cue ball will curve due to the combination of spin and slight elevation. The curve will stop when the cue ball is rolling smoothly on the cloth.

It is a little tricky to understand that the cue ball can be both spinning with side spin and rolling smoothly on the cloth. The best visualization helper I've seen is from Ron Shepard: Imagine a barrel like a 55-gallon cylindrical drum. Tilt it to the side about 20 degrees and start rolling it forward. It is both spinning and rolling smoothly on the ground. A pool ball can do the same thing.
Click to expand...
Ron's image (or was it Mike Page's?) is what finally clicked with me. It helps me to imagine the barrel contained within a sphere with its top and bottom edges touching the outside surface like latitude lines.

pj
chgo
 
ENGLISH!
To me, & apparently to others, anything not on the exact verticle axis is a form of side spin while it seesm that the 'science' community seem to consider a ball spinning only on the horizontal axis a 'side spin'.
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I don't know of anybody in the "science community" who thinks that. Since a ball can't have "pure" sidespin unless it's sliding with no forward or backward rotation, that definition would eliminate just about all sidespin shots.

pj
chgo
 
"It depends upon what the definition of "is" is"

It's been a fun and interesting discussion and I hate to delay the ending of it but....

The STUN SHOT is one of the most important shots in pool and most people describe the stun shot as a shot where the cue ball is "sliding" when it makes contact with the object ball. They also state that the cue ball will not have forward or backward rotation for the stun shot to be effective and for the the cue ball to follow the tangent line.

The "pool definition" of a sliding cue ball that most pool players understand is one where the cue ball has no forward or backward rotation.

In the pool world, I think it is an injustice to consider the cueball with backspin as a "sliding cueball".

Keep in mind, that I am not contesting the technical definition of "slide" as it relates to the physics of pool but for the purpose of describing a stun shot, perhaps the word "sliding" should be removed from all of the glossaries and text books. :rolleyes: Or better yet, for the common good of pool, a sliding cueball should be described as one that has no forward or backward spin.

These are the type of discussions that make AZ Billiards Main Forum THE WORLD'S BEST POOL FORUM. :wink:

I thank everyone for their intelligent, insightful and civil posts.
 
Following the tangent line...

JoeyA said:
It's been a fun and interesting discussion and I hate to delay the ending of it but....

The STUN SHOT is one of the most important shots in pool and most people describe the stun shot as a shot where the cue ball is "sliding" when it makes contact with the object ball. They also state that the cue ball will not have forward or backward rotation for the stun shot to be effective and for the the cue ball to follow the tangent line.

The "pool definition" of a sliding cue ball that most pool players understand is one where the cue ball has no forward or backward rotation.

In the pool world, I think it is an injustice to consider the cueball with backspin as a "sliding cueball".

Keep in mind, that I am not contesting the technical definition of "slide" as it relates to the physics of pool but for the purpose of describing a stun shot, perhaps the word "sliding" should be removed from all of the glossaries and text books. :rolleyes: Or better yet, for the common good of pool, a sliding cueball should be described as one that has no forward or backward spin.

These are the type of discussions that make AZ Billiards Main Forum THE WORLD'S BEST POOL FORUM. :wink:

I thank everyone for their intelligent, insightful and civil posts.
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As I have not really done any testing and rely on my intelligence and experience and ability to visualize for my knowledge, Dave may be able to answer this as to the reason...

When the ball is following the tangent line perfectly it is due to it being stunned; however, when there is follow OR draw on the CB, the harder you hit it, the longer it will follow the tangent before the follow and draw take effect.

Since there is follow or draw, it's not because it's a stun shot, so the question would then be, WHY is it following the tangent. My guess would be that it has something to do with more angular momentum due to increased force from greater acceleration but as I said, maybe Dave can shed some more light as to the why.

Jaden
 
ENGLISH! said:
Hi Dave,

Do you mean that a ball rolling an a diagonal axis rolls in a straight line and does not gradually stray off of that straight line.

Also, it seems to me that there is a different meaning to many as to just what is meant by 'side spin'. To me, & apparently to others, anything not spinning exactly verticlly is a form of side spin while it seems that the 'science' community seems to consider only a ball spinning exactly horizontally as 'side spin'. I'm not referring to just this thread but in general. Maybe a clarification 'thread' is in order. If I missed it, please excuse me & forget it.

Best Regards,
Click to expand...

Sorry, I typed that after only one(1) cup of coffee & was obviously in brain fart mode & had my axis up my ass. Please see the corrections in blue.
 
Patrick Johnson said:
Ron's image (or was it Mike Page's?) is what finally clicked with me. It helps me to imagine the barrel contained within a sphere with its top and bottom edges touching the outside surface like latitude lines.
Click to expand...
PJ,

Here's a pertinent (and well written) quote from you paraphrasing Mike Page on the "spin," "slide," and "roll" resource page:

Imagine that there's a cylinder (like a barrel) exactly the right size so that it's just contained within the ball. The cylinder/barrel's top and bottom edges meet the ball's surface like two latitude lines drawn around a globe in the northern and southern hemispheres.

Now imagine that you've tilted the barrel and are rolling it along the table's surface like you'd roll a barrel on its edge. You can see that the axis of rotation is tilted, and the barrel's bottom edge rolls along the table in a straight line without sliding at all.

Now imagine the ball surrounding the barrel rolling along with it across the table. This is how a ball rolls across the table with sidespin - no sliding, just rolling. If you were to put wet ink on the table it would mark a line around the ball at its "southern latitude" line.

The remaining wrinkle is that as the ball rolls its sidespin wears off and its axis of rotation becomes more and more horizontal. To visualize this, imagine that the tilted barrel within the ball tilts more and more onto its side, and simultaneously becomes fatter and fatter and shorter and shorter, but it continues rolling on its edge (you should be able to visualize doing this with a barrel that changes this way as you roll it). Eventually, when all the sidespin wears off, the fatter, shorter barrel becomes a flat disc rolling vertically on its edge. The wet ink line marked on the ball is actually a spiral that starts as a small tilted latitude and becomes a vertical "great circle" longitude when the ball is rolling normally without sidespin.​

Regards,
Dave
 
Jaden:
...when there is follow OR draw on the CB, the harder you hit it, the longer it will follow the tangent before the follow and draw take effect.
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Technically, it begins curving immediately at any speed, but at higher speed the curve is elongated so it's less visible to us. I don't mention this to pick nits (who, me? :)), but because it might help to visualize the details.

pj
chgo
 
ENGLISH! said:
dr_dave said:
A CB struck off center slides only until forward roll develops (which very soon for above-center hits) and during swerve (which happens over a very short distance for slow speed shots). After slide and swerve, the CB rolls with sidespin in a straight line with no slip whatsoever. For more information and video demonstrations, see:
Click to expand...
Hi Dave,

Do you mean that a ball rolling an a diagonal axis rolls in a straight line and does not gradually stray off of that straight line.
Click to expand...
That is correct (except on old-style cloths with heavy and directional nap). For an explanation and demonstration, see:

ENGLISH! said:
Also, it seems to me that there is a different meaning to many as to just what is meant by 'side spin'. To me, & apparently to others, anything not on the exact verticle axis is a form of side spin while it seesm that the 'science' community seem to consider a ball spinning only on the horizontal axis a 'side spin'.
Click to expand...
Sidespin is rotation about a vertical axis. The spin takes place in the horizontal plane, but it is about the vertical axis. Sidespin can occur simultaneously with either top, bottom, and/or masse spin. Each is about a different axis. The combined effects of multiple spin components results in rotation about some other axis, but the individual components are still there. The following video explains and demonstrates this fairly well:

Enjoy,
Dave
 
JoeyA said:
It's been a fun and interesting discussion and I hate to delay the ending of it but....

The STUN SHOT is one of the most important shots in pool and most people describe the stun shot as a shot where the cue ball is "sliding" when it makes contact with the object ball. They also state that the cue ball will not have forward or backward rotation for the stun shot to be effective and for the the cue ball to follow the tangent line.

The "pool definition" of a sliding cue ball that most pool players understand is one where the cue ball has no forward or backward rotation.

In the pool world, I think it is an injustice to consider the cueball with backspin as a "sliding cueball".

Keep in mind, that I am not contesting the technical definition of "slide" as it relates to the physics of pool but for the purpose of describing a stun shot, perhaps the word "sliding" should be removed from all of the glossaries and text books. :rolleyes: Or better yet, for the common good of pool, a sliding cueball should be described as one that has no forward or backward spin.
Click to expand...
I think the definitions and interpretations depend on who you are talking to in the "pool world." I personally believe the following definitions (from my online glossary) are consistent with both a physics understanding and how most of the "pool world" describes things:
natural roll: rolling motion of a ball where there is no sliding between the ball and the table cloth.

sliding: relative motion between the bottom of a moving ball and the cloth resulting in friction. Sliding occurs any time the ball is not rolling naturally.

skid: term used to describe the sliding motion of an object ball due to throw or cling.

stun shot: a shot where the cue ball has no top or bottom spin (i.e., it is purely sliding) when hits the object ball. A stun shot is also called a “stop shot at an angle.”​

I probably won't be changing these, but thank you for the suggestion. :wink:

Regards,
Dave

PS: You apparently didn't get the answer you wanted in this thread. :cool: You should do a little more research the next time you make a bet. :D
 
Patrick Johnson said:
Technically, it begins curving immediately at any speed, but at higher speed the curve is elongated so it's less visible to us. I don't mention this to pick nits (who, me? :)), but because it might help to visualize the details.
Click to expand...
Good answer. For those interested, more info, illustrations, and video demonstrations can be found here:

Enjoy,
Dave
 
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