Rarelymisses said:
Would you please say this again in a different way ? I just cannot understand what you said.
Sure.
When the cueball collides with the object ball, on the vast majority of shots the cueball's surface at the point of contact is moving across the object ball's surface, creating friction. So there is a relative surface speed between the balls at the point of contact. Of course, everyone aware of throw knows this. The effect of this friction is to reduce this surface speed during the period of impact. It does this by changing the spin and the speed along the tangent line of both balls (of course the object ball has no spin or speed to begin with so it "changes" them from zero to some value). If the relative surface speed is not too great to begin with, it reduces it to zero and the balls end up rolling across each other. At this point the friction is also reduced to essentially zero. Yes, this all happens in about .0002 seconds.
Now suppose the friction is greatly increased because of chalk or something. In those cases where the balls would end up rolling across each other under normal friction anyway, the only effect of the increased friction is to bring them to a rolling state faster. The result is no change in the amount of throw. The reason this is so is because the friction can do no more than to reduce the surface speed to zero. Once there, it ceases to exist. And whenever the balls end up rolling across each other, the speed imparted to the object ball along the tangent line (throw), whether we're talking about a horizontal or vertical tangent line, is a fixed fraction (1/7) of the initial relative surface speed.
For a medium speed straight-on shot, tip offsets of up to about 1/3 of maximum are within the range where this occurs. For hard shots, it's about 1/4 of maximum, and for soft ones about 1/2. This assumes that the cueball doesn't pick up much additional spin (follow) on the way to the object ball. When the cueball's spin is within this range, the shot is immune to skid effects. And this is pretty much true if the spin is just a little bit outside this range too. I believe you could take sandpaper to the balls, smear chalk over them, and not see any difference in throw.
In the case of pure topspin or draw on a straight-on shot, or pure sidespin on a cut shot, the amount of spin the cueball loses to the friction is also a fixed fraction when the balls end up rolling across each other.
Rarelymisses said:
I think you guys are on the right track. The problem seems to manifest on soft shots. .... On throw shots in the horizontal plane, there is less throw when the cueball is moving faster, so this should also be true in the vertical plane.
I think Flex was on track. I didn't think of it until he brought it up. I agree with your last statement, but speed alone does not give you immunity to skid. The spin has to be within the range(s) discussed above.
Hope that makes some sense. I can't go into the complete theory of throw, but see here if you want more info:
http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-14.pdf
The portion of the curves on page 9 (or 10) where the lines are straight are some of the cases where the balls roll across each other.
Jim