Scratched on the 8 ball to lose
- Thread starter berlowmj
- Start date
)
RE: 90 degree rule
When left/right English was mentioned, I believe the poster meant to hit a different contact point on the object ball. The cueball will still leave the object ball at 90 degrees, but it will be 90 degrees to a different slightly contact point. The throw from the English makes the ball still go in, despite the different contact point.
I hope that makes sense. What I'm saying is that side English does not affect the cueball path after contact and before a rail, assuming that the contact point is fixed. That I agree with. However, the assumption is that the shot will go in, not that the contact point is fixed.
Throw allows you to change the contact point and still make the shot. Since the contact point is changed, the cueball path will also be changed. JMHU (Just My Humble Understanding
)
When left/right English was mentioned, I believe the poster meant to hit a different contact point on the object ball. The cueball will still leave the object ball at 90 degrees, but it will be 90 degrees to a different slightly contact point. The throw from the English makes the ball still go in, despite the different contact point.
I hope that makes sense. What I'm saying is that side English does not affect the cueball path after contact and before a rail, assuming that the contact point is fixed. That I agree with. However, the assumption is that the shot will go in, not that the contact point is fixed.
Throw allows you to change the contact point and still make the shot. Since the contact point is changed, the cueball path will also be changed. JMHU (Just My Humble Understanding
)
Klopek said:Okay, but I've been predicting where my cueball will go within millimeters using these rules for a long time. I can tell you, the results are immediate and occur no matter how hard the cueball is struck. You're entitled to your opinion. Have a great Christmas day.
EDIT: It's of significant noteworthiness that the person who produced those video clips I posted is a Physics Professor. Perhaps you should write him and tell him he's wrong.
But i thought the harder you hit the more angle it produce.....
Sprite said:
Exactly! When you hit the ball harder the cue ball travels further along the tangent line until the spin takes over and bends the path forward or backwards. That's just one reason why for me, an abolute 30 degree angle on a rolling ball is a dog that just don't hunt!
RE: 30 degree rule
As far as I can tell, VIP's statements did not contradict the 30 degree rule (correct me if I'm wrong after this post). What I remember from the 30 degree rule from reading the article in Billiard Digest was this: Assuming a naturally rolling cueball, the angle between the cueball's initial path and the cueball's final path (before hitting a cushion, but after the natural roll takes over) will be approximately 30 degrees (call this angle Theta). This rule was stated to apply for hits between 1/4 ball and 3/4 ball.
They showed a plot of 'fraction of ball hit' vs. Theta for a range of thickness of hit. The plot looked similar to an "upside down" parabola. For a 1/4 ball hit, 1/2 ball hit and 3/4 ball hit, I believe Theta was about 28 degrees, 32 degrees and 28 degrees, respectively. I could be slightly off, but I remember it was pretty close to 30 degrees for that range of thickness of hit.
I don't think they mentioned anything about "offset". By offset, I mean, how far does that cueball "glance" after hitting the object ball. If you hit the cueball harder, it will glance further along the tangent line (sliding) before the forward roll takes over. However, no matter how much the cueball is offset by its glance, the 30 degree rule still applies. This last paragraph, I don't think was in the article, but is again JMHU.
As far as I can tell, VIP's statements did not contradict the 30 degree rule (correct me if I'm wrong after this post). What I remember from the 30 degree rule from reading the article in Billiard Digest was this: Assuming a naturally rolling cueball, the angle between the cueball's initial path and the cueball's final path (before hitting a cushion, but after the natural roll takes over) will be approximately 30 degrees (call this angle Theta). This rule was stated to apply for hits between 1/4 ball and 3/4 ball.
They showed a plot of 'fraction of ball hit' vs. Theta for a range of thickness of hit. The plot looked similar to an "upside down" parabola. For a 1/4 ball hit, 1/2 ball hit and 3/4 ball hit, I believe Theta was about 28 degrees, 32 degrees and 28 degrees, respectively. I could be slightly off, but I remember it was pretty close to 30 degrees for that range of thickness of hit.
I don't think they mentioned anything about "offset". By offset, I mean, how far does that cueball "glance" after hitting the object ball. If you hit the cueball harder, it will glance further along the tangent line (sliding) before the forward roll takes over. However, no matter how much the cueball is offset by its glance, the 30 degree rule still applies. This last paragraph, I don't think was in the article, but is again JMHU.
Last edited:
At a certain point yes, but like anything, all rules on the table have variables that change with speed and spin. The 30 & 90 degree rules are basic guidelines which can be quite accurate when you learn to capitalize on them through trial and error. Saying the cueball leaves at 90 degrees no matter what just goes against proven physics. Randyg said he thought the cueball always leaves at 90 degrees and VIProfessor agreed with him. This is what I took issue with.Sprite said:
My point to VIP was that the 30 & 90 degree rule stands up with a soft shot or a harder shot, as long as the cueball's rolling forward or has no roll at all respectively. Force follow is a different kettle of fish, but stun is stun. I didn't bring backspin up because it does vary dramatically depending on how hard the shot is played.
Fact is, denied or not, there is a 30 degree rule and a 90 degree rule, knowing about both of them and using them in your game will help prevent scratches.
Last edited:
If by "eventual path" you mean final direction, this is independent of its speed if the cueball is rolling before contacting the object ball, or in fact has any specific spin/speed ratio on it. It doesn't matter how fast or slow the cloth is either...well, at least to a pretty high degree of precision.VIProfessor said:
If by "eventual path" you mean its path on the way to reaching natural roll after impact, then of course you're right, this does depend on speed. But its final direction does not.
It might be noted that just about any statement made in this thread will be modified slightly if you look at the details close enough. For instance, if the cueball is still swerving after impact, then you could say its direction is affected by english, a masse shot being an extreme example of this.
Jim
Cuebacca said:
No correction of your post is necessary. I have no argument with your formulation of the "30 degree rule". What I was attempting to stress to Klopek, however, that regardless of the eventual path of the cue ball, the initial path of travel is on the 90 degree tangent line. As far as I know, the only exceptions to this are straight in shots and situations in which the cueball is airborne when it contacts the object ball.
You need to scroll back up and review those video links, I added a couple more after you responded to my post. The shots are played medium speed and there's clearly a huge difference in the cueball's path using stun hit and follow. You're denial seems naive or stubborn, either way, I'm not going to debate with you anymore. Good night.VIProfessor said:
WOW. You don't know what you don't know... as Randy G would say.Klopek said:You need to scroll back up and review those video links, I added a couple more after you responded to my post. The shots are played medium speed and there's clearly a huge difference in the cueball's path using stun hit and follow. You're denial seems naive or stubborn, either way, I'm not going to debate with you anymore. Good night.
What VIProfessor is saying is that immediately after impact, the cueball's direction is along the tangent line. It's not that obvious on a slight cut with a slowly rolling cueball, but nevertheless, that's the way it starts out. It's never absolutely true because of the less than perfect elasticity of the balls and the finite contact time. And as the cut angle is brought very close to zero, say a degree or two or three, you could say it's so untrue so as to be false. But otherwise it's a pretty accurate statement.Klopek said:You need to scroll back up and review those video links, I added a couple more after you responded to my post. The shots are played medium speed and there's clearly a huge difference in the cueball's path using stun hit and follow. You're denial seems naive or stubborn, either way, I'm not going to debate with you anymore. Good night.
Jim
Now that is a man of true knowledge!Jal said:
All in good fun buddy. I really don't care much of what angle the cueball leaves anything, as long as the object ball falls in the hole I am okay. 
Happy Holidays.
Happy Holidays.
Well, the harder you hit (all else equal) the longer the CB will slide instead of roll, so I don't see how this contradicts Klopek's point. Even if you are convinced that the initial departure is always on the tangent line, even for a rolling CB, the length of time it stays on the tangent line when the CB is rolling is so miniscule that for all intents and purposes it may as well simply be coming off at 30 degrees (i.e., it quickly, almost immediately, bends forward of the tangent line, following the 30 degree line).VIProfessor said:
Cory
It's all good. I look at it like this. Whether the cueball leaves at 90 or 30 or anything in between, it's what it does over the next few inches I care about.TannerPruess said:All in good fun buddy. I really don't care much of what angle the cueball leaves anything, as long as the object ball falls in the hole I am okay.
Cory in DC said:
As far as I know, no one in this thread said anything contrary to this. The disagreement, as I understood it at least, was about the immediate direction of the cueball after contacting the object ball. I assume that everyone agrees that after the (however momentary) initial direction the cueball takes along the tangent line, it can then alter its course off the tangent line in any number of ways.