Any proof of this? I think we need to have a CLEAR definition of what skid is then.
Lou said earlier it's ALL chalk. So are you contradicting him?
No, no proof, only what I feel is happening. I'm going to give it some detail here, and I'd love to hear from Bob J. or Dr. Dave regarding my accuracy or lack there of.
First of all, in my mind there are two (at least two) kinds of momentum / motion happening with a pool ball.
1. Directional momentum / motion. This can happen without the pool ball rolling, The ball can slide in a direction.
2. Rotational momentum / motion. This can happen without the pool ball moving in any particular direction, The ball can spin in place.
Ok, now there is the
Law of Inertia which if I'm close says .... An object at rest tends to stay at rest, while an object in motion tends to stay in motion. This is until an outside force acts on the motion.
Ok, now back to the two kinds of motion of the pool ball. We know they can exhibit either type of motion separately and independently of each other as well as together at the same time.
So, from that we can conclude that these motions don't necessarily have to commence at the same time.
Now back to the Law of Inertia. We have an Object Ball at rest. We now introduce a Cue Ball in motion approaching the OB at rest.
The CB is approaching with 2 (two) kinds of motion. Rotational as well as directional.
These two outside forces are about to act on the OB at rest. Doing so will inhibit the OB's tendency to stay at rest.
Which motion will act first on the OB? Rotational motion? Directional motion? Both together? One or the other independently?
I say given the right speed, angle, friction, if the rotational motion acts first on the OB the friction of the forward rolling Cue Ball can impart that gear type affect to the OB and cause it to jog backwards for just a fraction of a split second.
If that happens then it tries to come back to meet the CB as the CB passes they stay together ever so slightly throwing the OB off it's otherwise normal path.
If this phenomena is exaggerated enough the CB can actually climb up on the OB and thud as they meet.
Now, whether or not a particular dirt particle adds or removes surface friction in any specific situation is less important than the phenomena itself.
For example, a tiny microscopic spec of hard grit may actually reduce the contact area between the two balls and in doing so, reduce friction. In this case a dirty ball is less likely to skid.
Or, a larger dusty or dirty portion on a ball's contact point may not reduce contact area, but rather increase the friction of the two balls which would increase the likelihood of a skid with all other speed and angle factors favorable to the phenomena.
Regardless, I believe this skid is a product of these two separate types of motion working against each other for a split fraction of a second on the pool ball in certain circumstances.
That's my story and I'm sticking to it. :smile: