So cut induced throw overcoming spin induced? Or is there more to it?
whats the secret on cut shots on the short rail?
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So cut induced throw overcoming spin induced? Or is there more to it?
I'm not sure I'd say "overcoming". The motion of the surface of the cue ball on the object ball is a combination of the motion of its center and its spin.
The cb "pushing" or "shoving" the ob offline is the best way to describe cut-induced throw, because that's what's really happening -- the cb shoves the ob on its way through. A spinning cb can "throw" the ob, but that is different than cut-induced throw. That's why you can shoot a thin cut shot (to the left for example) using a little right and the cb will still shove the ob offline to the right. The spin reduces some of the shoving effect but doesn't eliminate it completely.
It's produced a different way, but it's all the same to the OB - the CB's surface rubs against the OB's surface, either because the CB is moving or because it's moving and spinning. The only difference the OB can "feel" is the total rubbing speed.
pj
chgo
The results are the same, but the OB has two different forces acting on it. I imagine I were an OB, sitting still, minding my own business, maybe wondering what it would feel like to roll across the cloth and drop into one of the pockets. While I'm daydreaming I suddenly get hit by a rolling CB with no spin on it. I start moving in a direction pretty close to 180° from the point of contact. If it's a perfect full ball collision, I will be sent exactly 180°. If it's a fractional collision I'll feel slightly shoved off of this 180° line due to the friction between my surface and the cb surface.
If the cb is sliding (stun), not rolling or spinning, I'll feel a stronger shove off line. If the cb is spinning backwards when it hits me, I'll feel less of a shove. If it's spinning in the same direction I'm being sent (inside english), I'll feel more of a shove (due to throw caused by english) than I would normally feel. If the cb is spinning opposite from the direction I'm being sent (outside english), I'll feel less of a shove off line because the cb will sort of spin off of me, decreasing the friction between us, and at the same time I'll feel the spin of the cb slightly throwing me back toward that 180° line.
There's one force: rubbing friction. If the results are the same, the force is in the same amount and direction, whether produced by speed alone or a combination of speed & spin.
pj
chgo
Rubbing friction in two separate vectors/directions is what I'm talking about as two different forces.
The results are the same as far as the ob being forced offline in relation to the contact point. There is always rubbing friction (cut-induced throw), and it's greatest when the cb is sliding into the ob. Shoot a cut shot with stun, then shoot the same shot at the same speed but with a rolling cb. We know we get less throw/shove with a rolling cb.
Now shoot the same cut at the same speed, but use outside english. We will still have the frictional force moving across the ob in the direction of cb travel (cut-induced throw), but we'll have an additional frictional force moving sideways across the surface of the ob (spin-induced throw) in the opposite direction of the cut-induced throw. One force is pushing the ob offline (years ago this should've been labeled the "shove" or "push" effect), and the other force is spinning/throwing the ob in the opposite direction. The spin-induced throw is a much smaller frictional force (unless the balls are filthy), but it's definitely a seperate force that opposes (or adds to if using inside spin) the typical collision-induced throw that occurs.
Oh, OK.
So far so good...
Maybe I misunderstand you, but the CB's surface can only rub across the OB's surface in one direction at a time, so there can only be a frictional force on the OB in one direction at a time.
As Bob mentioned, there are exceptions to the part in blue. Throw is reduced when the rubbing speed is too fast, which means that inside spin can actually reduce cut-induced throw and outside spin can actually increase it.
And since the physical forces of throw are identical in kind (rubbing friction between the balls' surfaces), I don't think it would clarify things to call them by different names - adding "cut-induced" or "spin-induced" to the word "throw" are accurate and instructive terms, I think.
pj
chgo
This can be a hard shot visually, especially when you are trying to do something with the CB - like hitting it very soft or with spin.
Set it up so you can visualize the shot better. I like to set up a 1/2 ball hit (using the poolology method) and shoot it like the rail is not there. With a ball's width between the OB and rail this should work fine.
Then, when you are making that well with no spin. Start moving the CB up table to create more and more of an angle. Shoot from each place until you are very confident with the shot. Eventually you won't be able to make it at all. Then go back to the beginning and shoot with inside english and do the same progression. Same with outside. Then vary speed and spin. Finally just throw the OB up and CB up in the general area and make the shot while playing for position for a 3rd ball that you can also move around.
This will not only help you make the shot it will also clearly illustrate when you should go for the shot and when you should find something else to do.
If you work on this for 30 minutes I bet you'll be cutting them in like a champ.
If you are still having trouble after that, find someone good to watch you shoot it. You probably have something mechanical going on that you need to sort out.
Wouldn't a cb with side spin and rolling into the ob have two frictional vectors upon collision? The resulting total friction being a combination of both forces? There is already a natural downward rolling frictional force when the cb hits the ob. Adding side spin to the cb introduces another frictional force in a different direction upon collision with the ob, but the rolling frictional force doesn't disappear.
And I don't think Bob was saying outside spin can actual "increase" CIT or inside spin could "decrease" it. I believe he was simply saying that on a thin cut, using a little outside spin (with the correct speed) you can still get quite a bit of CIT. But certainly not increase the CIT beyond what would naturally occur, unless of course you hit the shot firm enough to send the cb sliding into the ob with the outside spin still intact. Any side spin on the cb (inside or outside) on a thin cut at fast speed can decrease CIT. If he meant the righthand english would throw the ob more right than what the CIT would do, well....that'd have to be explained in another thread. Lol
Oh and I'm not suggesting to introduce new terms for the different action imparted on the ob. But I do believe it would clarify things for newbies when talking about "throw" and not including whether it's collision-induced ir spin-induced. Saying the cb pushes or shoves the ob a little offline is pretty simple to understand.
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The CB's surface rubs against the OB's surface in one direction only - for a rolling CB with side spin that direction is diagonally downward (rotating about the CB's tilted axis) - "vectors" are just a way of describing the combined single force.
It's implied by what he said - and true, regardless.
pj
chgo
Well, maybe but it is an incorrect understanding. That concept so far as I can figure makes the wrong prediction for moistening the contact point when balls throw. Saying that the surfaces are a little rough and the surface of the cue ball rubs across the surface of the object ball is both simple to understand and gives the correct predictions for various cases.
Let's look at the op's shot problem -- ob a couple of inches off the rail and less than a diamond from the corner pocket, cb about a foot away from it, a cut to the left. If we shoot the shot soft/slow speed with inside spin on the cb, the ob will have to provide frictional resistance to two forces at the point of contact -- one in response to the direction of the cb's path (resistance to CIT), and one in the direction of the tangential spin on the cb (resistance to SIT). In this case, both forces want to throw the ob toward the rail and that is the result we get, more friction and more throw than just rolling into the ob because there's another force at play during impact, not just the cb sliding over the ob.
If we shoot it with outside spin, the spin-induced throw counters the collision-induced throw, resulting in less total friction and less throw.
The resulting friction is always a combination of these two forces when spin is used. Any friction force is a vector, and the combination of multiple vectors gives a resultant. With the right speed and spin, we can reduce the total friction so there's minimal to zero amount of throw.
For a straight in shot (full ball contact) with side spin, the ob only has to provide resistance to the cb's tangential spin. The full mass of each ball, center to center hit, makes for no CIT, and so there's only one frictional force at the point of contact that could cause ob throw. But there is still a downward force at the contact point (or upward force if using draw) that the ob must respond to with some amount of resistance, it just doesn't affect throw.
I'll quit blowing up the thread now. Sorry to side track.
:embarrassed2:
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It works even with the ball on the rail - the cushion compresses enough to allow the slight overcut needed for throw.
pj
chgo
Yes. Correct.
You’re describing one force: rubbing friction between the balls’ surfaces. If you wet the contact point between the balls to eliminate the friction there will be no throw, cut induced or spin induced.
pj
chgo
I get what you're saying. I was suggesting "push" or "shove" to describe the result of this rubbing instead of "throw". But as long as "collision-induced" or "spin-induced" is used with "throw" it isn't ambiguous.
Honestly, what I've learned over the years, whether it's in education, work, musicianship, sports, etc.... most teachers and coaches teach straight from the book because that's how they learned. Others create new learning concepts.
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The exception to this demonstrates that collision-induced throw and cut-induced throw are the same force: for cuts thinner than half ball the rubbing speed from the collision is faster than optimum for throw - adding a little outside spin can slow the rubbing speed, actually increasing throw. Counterintuitive but true.
pj
chgo
Yes, rubbing friction. But sometimes this friction is a combination of two different directional forces across the surface of the ob.
I'm simply going by what I remember from Dr. Dave's and Bob J's data on throw when using various combinations of stun, roll, spin, or speed. There is always collision-induced throw on cut shots, which is caused by the cb rubbing against the ob (friction - the ob's resistance to the cb rubbing). Since spin can increase or decrease friction at the contact point, I believe it's because an additional force, another friction vector, requires the ob to respond according to the direction of the additional force, the resulting total friction being the combination of these forces. You don't believe it. I'm good with that.:thumbup:
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Makes sense. I'll have to dig through Bob and Dave's stuff to find the graphs I'm thinking of.