Cue ball control questions - 30 degree rule

NYCnoob99

Registered
I don't fully understand the 30 degree rule. Supposedly, it implies that any 1/4-3/4 cue ball thickness shot will deflect from aim line by 30 degrees or so, assuming it has forward spin.

But doesn't the amount of forward spin change the line of deflection (as demonstrated by drills like the wagon wheel drill)? So when exactly do we get 30 degrees? With a very very specific amount of forward spin? Can someone explain please?
 

Patrick Johnson

Fish of the Day
Silver Member
I don't fully understand the 30 degree rule. Supposedly, it implies that any 1/4-3/4 cue ball thickness shot will deflect from aim line by 30 degrees or so, assuming it has forward spin.

But doesn't the amount of forward spin change the line of deflection (as demonstrated by drills like the wagon wheel drill)? So when exactly do we get 30 degrees? With a very very specific amount of forward spin? Can someone explain please?
Start at Dr. Dave's 30-Degree Rule Resource Page. Here's a quote from there about your question:

"The 30° rule states that for a rolling-CB shot, over a wide range of cut angles, between a 1/4-ball and 3/4-ball hit, the CB will deflect by very close to 30° from its original direction after hitting the OB. If you want to be more precise, the angle is a little more (about 34°) closer to a 1/2-ball hit and a little less (about 27°) closer to a 1/4-ball or 3/4-ball hit."

pj
chgo
 

straightline

AzB Silver Member
Silver Member
I don't fully understand the 30 degree rule. Supposedly, it implies that any 1/4-3/4 cue ball thickness shot will deflect from aim line by 30 degrees or so, assuming it has forward spin.

But doesn't the amount of forward spin change the line of deflection (as demonstrated by drills like the wagon wheel drill)? So when exactly do we get 30 degrees? With a very very specific amount of forward spin? Can someone explain please?

Mathematical collisions in space will deflect only along the tangent lines. In pool there is the component of cloth friction and ensuing vectors.
The ball wants to continue in the direction in which it's heading and in this case, rolling. The collision subtracts from this 180* line. It can't add to it, nor can the forward roll do any better than the original 180 minus the collision. The 30 degree deflection is just the ball park for this collision angle and as DD points out, it's very easy to visualize.

Remember too, the balls are plastic and in fact bounce off each other. The harder the impact the bigger the bounce. Not the stuff of systems...
 

Patrick Johnson

Fish of the Day
Silver Member
Mathematical collisions in space will deflect only along the tangent lines. In pool there is the component of cloth friction and ensuing vectors.
The ball wants to continue in the direction in which it's heading and in this case, rolling. The collision subtracts from this 180* line. It can't add to it, nor can the forward roll do any better than the original 180 minus the collision. The 30 degree deflection is just the ball park for this collision angle and as DD points out, it's very easy to visualize.

Remember too, the balls are plastic and in fact bounce off each other. The harder the impact the bigger the bounce. Not the stuff of systems...
Kinda hard for me to tell exactly what you're saying. Here's a (hopefully) simplified explanation:

The CB always caroms off the OB along the tangent line, and will stay on it without top or bottom spin (i.e., a stun shot will scratch in the pic below). If the CB has top or bottom spin it curves off the tangent line after a few inches (or more for faster shots), curving forward with top spin and back with bottom.

The curved line labeled "FOLLOW" in the pic below ends up going a little less than 30° (not quite a 1/4 cut) for a medium speed rolling CB.

pj
chgo

Tangent.jpg
 
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straightline

AzB Silver Member
Silver Member
Just sayin' you can't overspin the ball and get more break. Actually a vertical stroke can create a burnout effect but that wasn't the idea. And the harder you hit the further out the carom holds before the ball breaks. Still don't quite know what noob99 wanted to know.

Love those diagrams. What are you using?
 

Patrick Johnson

Fish of the Day
Silver Member
...you can't overspin the ball and get more break.
Don't understand this.

...a vertical stroke can create a burnout effect
Or this.

the harder you hit the further out the carom holds before the ball breaks.
Yes, the harder you hit the farther along the tangent line the CB travels before curving off it.

Love those diagrams. What are you using?
Screen grabs from the Virtual Pool simulator + a simple drawing tool to add lines/text.

pj
chgo
 

straightline

AzB Silver Member
Silver Member
Burnout like car burnout. This would apply overspin thereby closing the 30 degree angle somewhat. Just saying with a normal stroke you can't get more spin than completely hooked up unless you shoot down and on the front part of the ball.

The second point; just trying to articulate that the balls do bounce off each other and the cue ball path is so influenced. I use the term "break" to describe the crossing over the original carom tangent.
 

Patrick Johnson

Fish of the Day
Silver Member
Burnout like car burnout. This would apply overspin thereby closing the 30 degree angle somewhat. Just saying with a normal stroke you can't get more spin than completely hooked up unless you shoot down and on the front part of the ball.
Oh, OK - got ya.

The second point; just trying to articulate that the balls do bounce off each other and the cue ball path is so influenced.
If "bounce off" means "caroms along the tangent line", then I agree. But if it means "bounce back", then I don't - for instance, the CB doesn't "bounce back" from a straight stop shot. It will bounce back some from a straight-on break shot, but that's because of the extra mass of the multiple racked balls.

pj
chgo
 

BC21

https://www.playpoolbetter.com
Gold Member
Silver Member
Oh, OK - got ya.


If "bounce off" means "caroms along the tangent line", then I agree. But if it means "bounce back", then I don't - for instance, the CB doesn't "bounce back" from a straight stop shot. It will bounce back some from a straight-on break shot, but that's because of the extra mass of the multiple racked balls.

pj
chgo

Funny thing.... I have a very light cb, around 3oz. It's funny to watch some of the wild action it gets. You can shoot a shot with top, and the cb bounces backward off the ob a good foot or more before the top spin kicks in and sends it forward. It's nearly impossible to run a rack with this ball.
 

Patrick Johnson

Fish of the Day
Silver Member
Funny thing.... I have a very light cb, around 3oz. It's funny to watch some of the wild action it gets. You can shoot a shot with top, and the cb bounces backward off the ob a good foot or more before the top spin kicks in and sends it forward. It's nearly impossible to run a rack with this ball.
And a CB that's heavier than the OB does the opposite: even with a straight shot and extreme draw spin it goes forward "through" the OB before reversing direction. The tangent line angle (normally perpendicular to the OB path) changes in the same ways.

pj
chgo
 

straightline

AzB Silver Member
Silver Member
If "bounce off" means "caroms along the tangent line", then I agree. But if it means "bounce back", then I don't - for instance, the CB doesn't "bounce back" from a straight stop shot. It will bounce back some from a straight-on break shot, but that's because of the extra mass of the multiple racked balls.

pj
chgo

The way I look at it, the balls do bounce so there is some conservation of energy going on that probably prolongs the travel along the original tangent. It may even have a reverse effect where the balls mush together and separate before they can decompress. This starts to get like CTE for position play so nevermind...:grin:
 

deraltefritz

AzB Silver Member
Silver Member
Funny thing.... I have a very light cb, around 3oz. It's funny to watch some of the wild action it gets. You can shoot a shot with top, and the cb bounces backward off the ob a good foot or more before the top spin kicks in and sends it forward. It's nearly impossible to run a rack with this ball.

In British 8-Ball, a noticeably smaller cue-ball is used. The effect is quite dramatic: https://youtu.be/bXkRxjz3x8E?t=9 and https://youtu.be/bXkRxjz3x8E?t=61

Do (American) coin operated bar boxes use a lighter or a heavier cue-ball?
 
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BC21

https://www.playpoolbetter.com
Gold Member
Silver Member

duckie

GregH
Silver Member
Knowing the angle doesn’t matter one bit. It just unnecessarily clutters the mind up with useless info.

The only thing that matters is the player knowing how to put the CB where they need it for the next shot.

And guess what..........learning to do that takes table time. You know hitting lots of balls. Something that most seem to think is not important to mastering pool.
 

BC21

https://www.playpoolbetter.com
Gold Member
Silver Member
Knowing the angle doesn’t matter one bit. It just unnecessarily clutters the mind up with useless info.

The only thing that matters is the player knowing how to put the CB where they need it for the next shot.

And guess what..........learning to do that takes table time. You know hitting lots of balls. Something that most seem to think is not important to mastering pool.

I agree 100% that knowing the angles is unnecessary clutter, that just recognizing the shot and knowing where the cb needs to be is what matters.

And yes it takes table time, hitting countless balls, especially for old school traditional trial and error aiming methods, HAMB, where you don't start becoming consistent until you reach a certain experience level where you're making more shots than you're missing.

But if a player could reduce or eliminate much of those early misses caused by inexperience or faulty guesswork, then consistency can come much quicker. In other words, rather than aiming where you think you need to aim, only to miss over and over again until you build enough positive experience to know where to aim, a player could start off already knowing exactly where to aim, bypassing the old time-consuming trial and error learning method/experience. It will still require table time, because the stroke is most important, and it requires time to groove.
 
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