Skid

[oceanweb]

What can be done to reduce it? I’ve missed shots and/or position on the most simple shots due to %$#& skid. My regular opponent says that outside english reduces or eliminates skid. I don’t think so. I believe that skid is caused by residual chalk on the cueball coming between the contact points of the cueball and object ball. I’ve watched the cueball climb right up an object ball due to this. If that is true then what good will outside English do?

I've never witnessed a cueball climb up an object ball. The appearance of cue balls climbing object balls is better known as the "budweiser effect".

But outside english will certainly reduce the amount of friction between the cueball and the object ball and therefore reduce the odds of the object ball skidding.

A little motherly advice never hurt either, "make sure you clean your balls son".

 

[pete lafond]

Also, if the cue ball climbs the object ball, are you sure that the cue ball is not air-born at contact? Are these hard follow shots or medium pace, or what?

QUOTE]

Seldom will occur on a firm shot. Happens on a slow roll shot. To answer you, the CB is not jumping.

While reading your post I realized another point; If the CB (Red dot) is lighter than object balls, skids are more often. This is fact. We changed to a heavier CB and skids are less often, though they still happen.

 

[pete lafond]

I find it interesting that nobody responded to my post about why there might be more skid on new cloth. Was my post difficult to understand ? Basically, I said that the minimal friction under the object ball on new cloth will allow the friction at the cueball-object ball interface to have a larger effect. When the object ball skids, it is the lateral movement of the object ball that is excessive. The only two things preventing this lateral movement normally are the inertia of the object ball and the friction underneath it. Take away the friction of the cloth and you have more lateral movement. Seems simple to me.

I am not sure about this because it should be earier for the OB to get out of the way sooner. Not saying you are wrong, just some more to think about.

 

[Neil]

..............

 

[oceanweb]

I find it interesting that nobody responded to my post about why there might be more skid on new cloth. Was my post difficult to understand ? Basically, I said that the minimal friction under the object ball on new cloth will allow the friction at the cueball-object ball interface to have a larger effect. When the object ball skids, it is the lateral movement of the object ball that is excessive. The only two things preventing this lateral movement normally are the inertia of the object ball and the friction underneath it. Take away the friction of the cloth and you have more lateral movement. Seems simple to me.

I think that you and Bob Jewitt need some "alone time".

 

[Aaron_S]

This is why I have never like the term "skid" for this. Skid sounds too much like... well like something skidding across the felt, which, while that may be a by-product of this situation, is IMO not the best descriptive for what's initially happening here. There are many other things that can cause a ball to skid across the felt, and I think that may be what's causing some of the confusion.

Of course, I'm running on the assumption that when you say "skid" you're referring to the same thing snooker players refer to as a "kick". If so, I believe we could find a better name for it that would be a little less confusing to those who are unfamiliar with it. It's simply a situation where the friction between two balls is artificially increased due to the presence of a foreign substance at the contact point, resulting in an abnormal hit. Shouldn't there be a better word than "skid" for that?

Aaron

 

[TheOne]

It's simply a situation where the friction between two balls is artificially increased due to the presence of a foreign substance at the contact point, resulting in an abnormal hit. Shouldn't there be a better word than "skid" for that?
Aaron

This is a pretty good description IMO, although we all don't agree on what is the most FREQUENT culprit, I think we're all on the same with regards your description.

Something like oils in the cloth that probably cover the whole surface of the balls makes it more likely an explanation IMO than a small dot of chalk. I wouldn't be at all surprised if the cause of kicks where something like this:

5% - bad surface contact, abrasion
10-20% - Chalk
75-85% - Oil or some other unknown such as static etc

From all the evidence I've seen this seems to fit best. But of course we still don't know what the main culprit is for sure.

 

[Rarelymisses]

First, we need to agree on a definition of skid. Let's say that you're shooting a 30 degree cut shot to the left corner pocket with center ball (no English). Because you know about contact-induced throw, you probably shoot the shot as if it were a 32 degree cut shot, and the object ball should take off on the 30 degree line into the heart of the pocket. But, if there is excessive friction, the object ball takes off on something like a 28 degree line (or more) and misses, and that is what we call a "skid".

We generally agree that dirty balls cause more skid, and that would be because of the excessive friction at the point of contact. We also know that acetone cleaned balls have more skid, and I suggest that this is because a clean ball also has more friction. I believe that any oil on the balls would only decrease throw and skid.

At the moment of contact in the 30 degree cut shot example above, the "normal" force at the point of contact is in the direction of the 32 degree line, and that is how the kinetic energy of the cue ball is transferred to the object ball. But the surface of the cue ball is sliding across the surface of the object ball too, so a force is applied at generally a right angle to that 32 degree line. This force is due to friction. When you add the kinetic energy vector and this force vector together, you get the resultant line that the object ball will travel on. Notice that the frictional force is not pushing the object ball, but rather dragging it to the right (if cutting to the left).

Since the cue ball is trying to drag the object ball to the right, the object ball can only resist with 2 things: its inertia, and the friction of the cloth under the object ball. The inertia is a constant. The friction of a new cloth is minimal, so there should be more drag (what we call skid) on a new coth. That would explain why TV conditions and clean balls produce skid.
This could be tested by putting a glass plate on a pool table and wiping it with a light coat of oil to make it very slippery. Now place two object balls on the plate and freeze them together (make sure the contact point is clean). Shoot into them at a 30 degree angle with the cue ball and measure the amount of throw. Remove the glass plate and repeat the experiment with clean balls, and the amount of throw should be less (on an older cloth). The only difference in the two setups is the friction under the object balls, so I suggest that the glass plate would result in more throw. (took 30 minute break here to try it myself) ....I did this on my own table and was amazed at how well it worked. On a seven foot shot, the balls threw about 8 inches when sitting on oiled glass, but only about an inch when sitting on the cloth. Now somebody out there can get a plate of glass and replicate my experiment.

 

[Aaron_S]

5% - bad surface contact, abrasion
10-20% - Chalk
75-85% - Oil or some other unknown such as static etc

You may be right; I have just always assumed that chalk was the main contributor to this phenomenon. The fact that kicks are, at least in my experience, such rare occurences leads me to believe that they are due to a rare set of circumstances. If they were simply due to oil or dirty balls, I would expect them to occur far more often. Also, and I'm not a physics guy, but when I think of oil I think of a lubricant, which I would expect to cause a reduction in friction rather than an increase. Unless, of course, there was some stickiness or abrasiveness due to other foreign substances in the oil, like chalk for instance.

One thing to consider is that kicks also occur under premium conditions, like at the Crucible where the table is immaculate, the felt is new, and a referee is constantly wiping down the cueball throughout the match. That should greatly limit the number of foreign substances that could possibly be on the cueball at any given time.