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

JoeyA

JoeyA

Efren's Mini-Tourn BACKER
Silver Member
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,
 
Well....

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...

Hmm. The best most accurate answer, is that when it is sliding, it is sliding and when it is rolling it is rolling.

When you first strike the ball, it is sliding regardless as to where you hit it. It starts rolling when friction overcomes its momentum.

The momentum will be directional depending on what type of English is put on it.

A stun shot starts off sliding the harder it is hit, the longer it will slide before friction causes it to start rolling.

The same can be said for a follow or a draw to greater degrees.

Jaden

p.s. I suppose that it is possible for it to be rolling RIGHT off the bat with follow, if the follow is directly proportional to the speed of the hit and equal to the amount of friction necessary to have a different portion of the ball in contact with the felt at all times.

Any time the rate of spin on the ball is more or less than its directional velocity, it is sliding.
 
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Jaden said:
Hmm. The best most accurate answer, is that when it is sliding, it is sliding and when it is rolling it is rolling.

When you first strike the ball, it is sliding regardless as to where you hit it. It starts rolling when friction overcomes its momentum.

The momentum will be directional depending on what type of English is put on it.

A stun shot starts off sliding the harder it is hit, the longer it will slide before friction causes it to start rolling.

The same can be said for a follow or a draw to greater degrees.

Jaden

p.s. I suppose that it is possible for it to be rolling RIGHT off the bat with follow, if the follow is directly proportional to the speed of the hit and equal to the amount of friction necessary to have a different portion of the ball in contact with the felt at all times.

Any time the rate of spin on the ball is more or less than its directional velocity, it is sliding.
Click to expand...

Perfectly simple and accurate explanation. +1
 
A ball is sliding when it is traversing the cloth at a rate different than it is spinning on the axis perpendicular to the direction over the cloth. This spin rate can be backwards or forwards or absolutely zero spin.

A ball is rolling when the spin rate and the traversal rates are equal.

A ball struck with a level cue at about the 65% point will roll immediately. The force from the cue hitting the ball high adds enough loading to the contact point that the ball is pushed away already rolling.

Anything lower than this point and the ball will be sliding with draw, anything higher than this point and the ball will be sliding with follow.

A ball sliding across the cloth will have a force applied at the contact point that will change the slide into a roll. A ball sliding with draw will slow down before beginning to roll, a ball with follow will speed up. In both cases angular momentum is converted into velocity.

Consider applying draw to a shot:: As the CB leave the cue, it is spinning backwards and over some distance this backspin will decrease to xero. Shortly afterwards the pure sliding ball, starts to roll at the rate it is moving.

If you make contact with the OB at precisely the point where the CB has no back spin and also no forward spin, it is known as a stun shot.
 
I'm all for learning BUT

I think alot of missed shots are blamed on "skid" ,"slide" , or a case of old or new cloth.You either hit it right or you don't .;)
 
Before I answer let me try to define what "roll" means to me:

The ball has a diameter and it is perfectly round. At its biggest diameter the ball has its perimeter. The ball can have a liniar speed that tells how fast it moves in direction of the table's plane surface. Parallel the ball can have an additional rotation speed (meassured at the ball's perimeter) by rotating around its own axis. There is an endless number of axes' directions in relation to the table's surface. In my definitions the ball rolls purely if there is following situation: The linear speed of the ball is in direction and ammount exactly the same as the ball's rotating speed. If the ball has a difference between linear speed and rotating speed in only one of these two - direction of speed or ammount of speed - the ball does slide and not roll.


Your questions:

1. When you roll the cue ball across the table, is it "sliding"?
--> At the beginning it probably slides shortly at the moment when you accelerate the ball, for example by throwing it onto the table by hand. After a certain time the ball rolls. So in principle: the ball is not sliding, easily spoken.



2. When you stun the cue ball (hitting it with neither back spin or forward roll) is it "sliding"?
--> It is always sliding in the very first moment. The time it takes that the ball is rolling is depending on its linear speed, the grip of the cloth and the distance to the next rail.



3. When you put back-spin (draw) on the cue ball does the cue ball "slide" on its way to the object ball?
--> It is sliding in the very first moment. The time it takes that the ball is rolling is depending on its linear speed, the grip of the cloth and the distance to the next rail, and also from its rotation speed. The direction of the ball's rotating speed is at the beginning exactly reverse the the direction of its linear speed. By frictioning to the cloth the rotating speed slows down while the ball moves in linear direction. It can happen that the rotating speed slows down to zero and the ball is still moving into linear direction, and then the ball starts to rotate into the direction of the linear movement, also caused by friction.
 
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Jaden:
I suppose that it is possible for it to be rolling RIGHT off the bat with follow, if the follow is directly proportional to the speed of the hit and equal to the amount of friction necessary to have a different portion of the ball in contact with the felt at all times.
Click to expand...
It's even easy, and the same for any speed: just hit the cue ball 5/7 of the distance from its bottom to its top (40% of the distance from centerball to top, or 80% of the distance to the miscue limit).

Any time the rate of spin on the ball is more or less than its directional velocity, it is sliding.
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Yep. Other ways to say it might be:

A ball is sliding except when it completes one full forward rotation for each distance of forward travel equal to its circumference.

or...

A ball is sliding except when its forward rotational speed does not equal its forward speed of travel.

I think it's also correct to say a ball is sliding whenever it slips sideways on the cloth (with masse spin), whether or not it's sliding in the direction of its travel. So we could also say:

A ball is sliding any time there is slippage (or rubbing friction) between its surface and the table's surface.

pj
chgo
 
Matt90 said:
I think alot of missed shots are blamed on "skid" ,"slide" , or a case of old or new cloth.You either hit it right or you don't .;)
Click to expand...
"Skid" (exaggerated throw) isn't the same thing as normal sliding. Skid does cause misses even when the cue ball is hit accurately.

pj
chgo
 
JoeyA said:
1. When you roll the cue ball across the table, is it "sliding"? If you mean say lag speed, then the answer is no. Tho there are some off hand shots such as the drag draw that have slide in it on softer style shots.....which can be shot with a finished stroke.

2. When you stun the cue ball (hitting it with neither back spin or forward roll) is it "sliding"? When I stun the ball or when anyone else does its always sliding if its a perfect stun on impact. The CB can even have backspin prior to impact but it will always be at slide upon impact to provide stun.s

3. When you put back-spin (draw) on the cue ball does the cue ball "slide" on its way to the object ball? Joey honestly all three of these questions are all trick questions. YES SOMETIMES my CB slides when I put backspin on the rock. Which is more trickery of words as when I say backspin I mean LOW ENGLISH...but as we all know one can go as low as one wants and not get any backspin at all, IE: Crappy delivery and no acceleration of the cue stick to the delivery.

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...


In my definition of slide the latter person is what I lean to. Think about alot of stop shots........you stroke them and initially there is backspin and it then coasts with no spin and POP, hits the OB and stays dead.

-GG
 
I was going to say the same thing...

Patrick Johnson said:
"Skid" (exaggerated throw) isn't the same thing as normal sliding. Skid does cause misses even when the cue ball is hit accurately.

pj
chgo
Click to expand...

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
 
Patrick Johnson said:
It's even easy, and the same for any speed: just hit the cue ball 5/7 of the distance from its bottom to its top (40% of the distance from centerball to top, or 80% of the distance to the miscue limit).


Yep. Other ways to say it might be:

A ball is sliding except when it completes one full forward rotation for each distance of forward travel equal to its circumference.

or...

A ball is sliding except when its forward rotational speed does not equal its forward speed of travel.

I think it's also correct to say a ball is sliding whenever it slips sideways on the cloth (with masse spin), whether or not it's sliding in the direction of its travel. So we could also say:

A ball is sliding any time there is slippage (or rubbing friction) between its surface and the table's surface.

pj
chgo
Click to expand...

So when a cue ball is traveling forward and has back-spin on it as it travels across the cloth, is it sliding at that time or just sliding when the back-spin wears off?
 
It is sliding while it has back spin...

JoeyA said:
So when a cue ball is traveling forward and has back-spin on it as it travels across the cloth, is it sliding at that time or just sliding when the back-spin wears off?
Click to expand...

It is ROLLING once the spin wears off.

Jaden
 
JoeyA said:
So when a cue ball is traveling forward and has back-spin on it as it travels across the cloth, is it sliding at that time or just sliding when the back-spin wears off?
Click to expand...
Backward rotation and less-than-full forward rotation are both within the general definition of sliding. Sliding without forward or backward rotation is the specific sliding condition (within the general definition) called "stun".

Maybe non-stun sliding would be more clearly called slipping.

pj
chgo
 
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JoeyA said:
OK, is the cue ball sliding when it has back-spin on it?
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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.
 
Matt90 said:
I think alot of missed shots are blamed on "skid" ,"slide" , or a case of old or new cloth.You either hit it right or you don't .;)
Click to expand...

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.
 
A slippery slope indeed.

Patrick Johnson said:
Backward rotation and less-than-full forward rotation are both within the general definition of sliding. Sliding without forward or backward rotation is the specific sliding condition (within the general definition) called "stun".

Maybe non-stun sliding would be more clearly called slipping.

pj
chgo
Click to expand...

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,
 
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