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

JoeyA said:
This is what I was looking for. I predicted you would be the one who would give the greatest clarification. Ok, at a minimum, it is what I hoped would be said about slide and draw. :smile:

I think also about force-follow, where perhaps the cue ball is hit with force-follow toward a rail and when the cue ball hits the rail, the cue ball bounces off a short distance with the force-follow still in tact and momentarily sits there, spinning with forward rotation and slipping, not sliding; but that's different as well.

The back-spin example at least has a forward momentum going for itself, unlike the slipping, force-follow example above.

To confess, I was the other person who whined that when the cue ball had back-spin on the cue ball, it was not sliding. I always considered the cue ball sliding when it had no back spin and no forward roll. The other person, a good friend, wailed a way at me and complained that the cue ball even with draw was sliding. We had a bet that we would make declarations (about how wrong we were) to ten different people at ten different times if one of us was wrong. Now, maybe both of us have an excuse for weaseling out of the bet. :D;)

Thanks,
Click to expand...

to me when the force follow cue ball comes off the rail it is spinning as if hit with draw ie moving forward (away from the rail) but spinning backward)towards the rail) if draw is sliding then your force follow shot would also be sliding
jmho
icbw
p.s. i would have voted for only balls with no spin are sliding
 
Joey,

Glad you got the answer you were looking for. Who wiil be 'more' weasling?

To me, draw spin while moving foward would be better called skipping.

Moving foward with no back spin or foward roll would be skidding like when you slam on the brakes of an older car without ABS brakes.

Hope to run into you & Mr. L&L soon. I saw the you tube interview. It was great.

Best Regards,
 
bbb said:
to me when the force follow cue ball comes off the rail it is spinning as if hit with draw ie moving forward (away from the rail) but spinning backward)towards the rail) if draw is sliding then your force follow shot would also be sliding
jmho
icbw
p.s. i would have voted for only balls with no spin are sliding
Click to expand...

I see your point about "sliding".
 
Simple Answer:

Sliding= Friction between ball and cloth is kenetic.
Rolling= Friction between ball and cloth is static.
 
Dr. Dave

ENGLISH! said:
Joey,

Glad you got the answer you were looking for. Who wiil be 'more' weasling?

To me, draw spin while moving foward would be better called skipping.

Moving foward with no back spin or foward roll would be skidding like when you slam on the brakes of an older car without ABS brakes.

Hope to run into you & Mr. L&L soon. I saw the you tube interview. It was great.

Best Regards,
Click to expand...

We'll have a good time, discussing who is the biggest weasel. :D

That's the interesting thing about vocabulary and definitions. Everyone has their own interpretation but good communication is important.

I suppose this is as good a time as any to give props to someone who has provided some of the most carefully crafted definitions of pool terms and that is David Alciatore (“Dr. Dave”) http://billiards.colostate.edu/

His glossary is second to none.

Dr. Dave has created a voluminous array of pool related information that is available for free to those who are searching but he also sells some EXCELLENT pool instructional DVDs and a book as well.

Dr. Dave's answers to frequently-asked questions (FAQs),
mostly from the BD CCB and AZB discussion forums

maintained for the book: The Illustrated Principles of Pool and Billiards,
the DVD series: The Video Encyclopedia of Pool Shots (VEPS),
the DVD series: The Video Encyclopedia of Pool Practice (VEPP),
and the monthly Billiards Digest "Illustrated Principles" instructional articles

Any of the DVD series would make a great Christmas gift for any serious pool aficianado.
 
nrhoades said:
Simple Answer:

Sliding= Friction between ball and cloth is kenetic.
Rolling= Friction between ball and cloth is static.
Click to expand...

Nice. Do you have another for when the cue ball has back-spin but is going forward? JoeyA likes "slipping". lol
 
The definitions that make the most sense from a physics perspective are:

Rolling: when the forward rotation in the direction of motion matches that forward motion.

Sliding: when the rotation doesn't match the motion.

When a ball is rolling, its speed is not changing quickly. When a ball is sliding, its speed is changing quickly. The speed may be increasing or decreasing. In the case of draw on the cue ball before it has struck the object ball, the speed is rapidly decreasing. In the case of the drawn cue ball just after it has struck the object ball full, the speed is increasing (back towards you).

One interesting aspect of billiards is that the side spin can be treated entirely separately and does not seem to enter into the rolling/sliding condition at all.
 
JoeyA said:
1. When you roll the cue ball across the table, is it "sliding"?

2. When you stun the cue ball (hitting it with neither back spin or forward roll) is it "sliding"?

3. When you put back-spin (draw) on the cue ball does the cue ball "slide" on its way to the object ball?

The argument is that one person claims that when the cue ball is "rolling" it is not sliding, it is only "rolling" but when you draw the cue ball, even though the cue ball has back spin on it, it is sliding as it goes to the object ball.

The other person claims that the cue ball only slides when there is no back spin or forward roll.

Everyone is invited to give their answers.

Thanks,
Click to expand...

1) No. Sliding implies that there is movement of the surface of the ball relative to the cloth. This does not occur in a rolling ball. The *surface* of the ball does not move relative to the cloth.

2) Usually stun involves sliding.

3) Draw always involves sliding. The surface of the ball is moving across the cloth.

Think of it this way. Take a piece of chalk. If you roll the chalk on the table, it doesn't make a mark. If you slide it across the table, it does make a mark.

KMRUNOUT
 
Jaden said:
Skid is more of a tangential slide due to the CB coming in at an angle and striking the OB...

It throws the OB off of its intended path in an unpredictable manner...

Jaden
Click to expand...
Yes, but throw and skid refer to the changed direction of the object ball, not to its sliding condition. The object ball slides a little whenever it's hit by the cue ball - the amount of sliding with skid can be the same, more or less than with normal throw, depending on whether the cue ball has forward or backwards rotation.

pj
chgo
 
Last edited:
JoeyA said:
3. When you put back-spin (draw) on the cue ball does the cue ball "slide" on its way to the object ball?
Click to expand...

What you've described here is of course "backsliding", in which the CB relapses into bad habits, sinful behavior, or undesirable activities.
 
Bob Jewett said:
The definitions that make the most sense from a physics perspective are:

Rolling: when the forward rotation in the direction of motion matches that forward motion.

Sliding: when the rotation doesn't match the motion.

When a ball is rolling, its speed is not changing quickly. When a ball is sliding, its speed is changing quickly. The speed may be increasing or decreasing. In the case of draw on the cue ball before it has struck the object ball, the speed is rapidly decreasing. In the case of the drawn cue ball just after it has struck the object ball full, the speed is increasing (back towards you).

One interesting aspect of billiards is that the side spin can be treated entirely separately and does not seem to enter into the rolling/sliding condition at all.
Click to expand...

What about when the cue ball is stunned with no back-spin or forward roll? Is the speed changing quickly? I guess so, just not as quickly as a drawn cue ball headed to an object ball.

Oh well.....I'm ready anyway.

picture.php


I'll guess, I'll have to concede to my friend. :smile:
 
I think there's an issue with semantics here. It's easier to define when a ball is rolling and then label all other scenarios as when the ball is "skidding".

A ball will rotate on its axis at a rate of Pi*Diameter per unit of time.

That ball is rolling only when the linear distance the center of the ball travels is equal to that rotational distance in the same unit of time.

I'm assuming that the linear distance is perpendicular to the axis of the rotation here (i.e. if the axis of the ball is rotating on the z axis, the center of the ball is traveling on the x or y axes).

E.G. A typical cue ball has a diameter of 2.25 inches. The circumference, C, of that cue ball is then 2.25 in * Pi = 7.068583 in. If the ball is rotating at C/s, then the ball is rolling if the center of the ball is traveling linearly at the same rate of 7.068583/s.

A ball hit with draw is skidding because it's rotating at a negative rotational distance relative to the path of travel of the center of the ball. A ball hit with "stun" is skidding because it's rotating at 0 (not rotating at all). Strictly speaking, a ball hit with follow is still "skidding" because it's rotating at a greater rate then the center of the ball is traveling linearly.

Taek
 
Last edited:
There's physics and there's pool terminology.

In pool terminology your last person is correct: a ball is sliding when there is no forward roll or backspin.

In physics a billiard ball would always have some amount of slide regardless of its spin. During forward or backspin it might only be 0.001%, but it's there. Conversely, it's impossible for a ball to have absolutely no forward spin or backspin. Again, the amount might only be 0.001%, but it does exist. It comes down to how fine a timeframe you're using to measure.

Dr. Dave would probably have the best answer.
 
ENGLISH! said:
Joey,

You did not get it after all of that.:wink:

There's skidding, sliding, & rolling. Which one where & when? Pick a spot, or should I say a place in time.:wink:

Best Regards,
Rick

PS Maybe we should add or insert slipping.
Click to expand...

"Skidding" and "sliding" (and "slipping") are synonymous. (In most but not all dictionaries)
 
JoeyA said:
What about when the cue ball is stunned with no back-spin or forward roll? Is the speed changing quickly? I guess so, just not as quickly as a drawn cue ball headed to an object ball.

Oh well.....I'm ready anyway.

...
I'll guess, I'll have to concede to my friend. :smile:
Click to expand...
When the cue ball is stunned into an object ball with a cut angle, the cue ball leaves the object ball without roll. It will slow down about as a fast as a ball with draw slows down or a following cue ball picks up speed after a full hit. Another way to say that is that the frictional force on the bottom of the ball is more or less a constant value until the ball is rolling smoothly. Then the frictional force becomes purely a different type (rolling) and is a lot smaller.

I suppose if you want to describe more situations you could talk about "partial follow" "pure slide" "standard draw" and such. I like to refer to "unit draw" as being the same amount of draw as a rolling ball would have follow at the same cue ball speed. That is almost as much draw as you will ever get on the cue ball.

A stunned cue ball will slow down to 5/7ths of its original speed off the object ball as it pickups natural roll.
 
Joey,

I know others have already answered most of the questions, but here are my answers anyway:

JoeyA said:
1. When you roll the cue ball across the table, is it "sliding"?
Click to expand...
No. If the ball is "rolling," then it is not "sliding." Sliding occurs only when there is relative ("sliding") motion between the base of the ball and the cloth (creating sliding friction).

JoeyA said:
2. When you stun the cue ball (hitting it with neither back spin or forward roll) is it "sliding"?
Click to expand...
Yes, until it starts rolling (after sliding enough for roll to develop).

JoeyA said:
3. When you put back-spin (draw) on the cue ball does the cue ball "slide" on its way to the object ball?
Click to expand...
Yes, until it starts rolling (after sliding enough for roll to develop).


FYI, illustrations, demonstrations, and supporting resources related to all of the questions in this thread can be found here:

Regards and Happy Holidays,
Dave
 
dr_dave said:
If the ball is "rolling," then it is not "sliding." Sliding occurs only when there is relative ("sliding") motion between the base of the ball and the cloth (creating sliding friction).
Click to expand...
One thing I would add is that the phrase "pure sliding" could be used to describe "stun," where the ball is sliding with absolutely no top or bottom spin. For example, with a perfect stop shot, the CB has perfect "stun" or "pure slide" at the moment of contact with the OB.

Regards,
Dave
 
JoeyA said:
I suppose this is as good a time as any to give props to someone who has provided some of the most carefully crafted definitions of pool terms and that is David Alciatore (“Dr. Dave”) http://billiards.colostate.edu/

His glossary is second to none.

Dr. Dave has created a voluminous array of pool related information that is available for free to those who are searching but he also sells some EXCELLENT pool instructional DVDs and a book as well.

Dr. Dave's answers to frequently-asked questions (FAQs),
mostly from the BD CCB and AZB discussion forums

maintained for the book: The Illustrated Principles of Pool and Billiards,
the DVD series: The Video Encyclopedia of Pool Shots (VEPS),
the DVD series: The Video Encyclopedia of Pool Practice (VEPP),
and the monthly Billiards Digest "Illustrated Principles" instructional articles

Any of the DVD series would make a great Christmas gift for any serious pool aficianado.
Click to expand...
Joey,

Thanks for the props. I appreciate it.

Catch you later,
Dave
 
You must log in or register to reply here.
Back
Top