Question for Dr. Dave RE: CB-OB distance traveled

B

bdorman

Dead money
Silver Member
I was thinking about this earlier today and wanted to run it by you: Is the following true?

"For a rolling CB the total distance traveled (CB + OB) is always equal regardless of cut angle."

Simple conservation of energy? Missing factors? a) of course, draw on the CB will introduce friction; that's why I specified "rolling CB." b) ignores the effect that hitting a cushion has on distance, c) other?

(I thought about this while thinking about safety play...waiting to drive my wife home from her dentist appointment...)

Thanks.
 
bdorman said:
I was thinking about this earlier today and wanted to run it by you: Is the following true?

"For a rolling CB the total distance traveled (CB + OB) is always equal regardless of cut angle."

Simple conservation of energy?
Click to expand...
Good idea; but, unfortunately, it is not true. After contact, the CB slides some as it curves or follows forward. This involves energy loss. Also, the OB starts out with stun and loses energy during sliding before it develops full roll. If you want to see the full analysis, with lots of interesting plots, see:

TP A.16 - Final ball speeds, distances, and directions for natural roll shots

FYI, there are still several useful principles related to CB and OB travel distances. They are described here:

ball speeds and travel distances

Regards,
Dave
 
dr_dave said:
Good idea; but, unfortunately, it is not true. After contact, the CB slides some as it curves or follows forward. This involves energy loss. Also, the OB starts out with stun and loses energy during sliding before it develops full roll. If you want to see the full analysis, with lots of interesting plots, see:

TP A.16 - Final ball speeds, distances, and directions for natural roll shots

FYI, there are still several useful principles related to CB and OB travel distances. They are described here:

ball speeds and travel distances

Regards,
Dave
Click to expand...

Many thanks!
 
Ron Swanson said:
Me too. My observation: players who can cue a ball get more energy into the OB than those who cannot. The OB picks up more speed than the CB loses upon contact.
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I think that is more a belief than an observation. By what percentage do the balls violate Newton's laws for players who can "cue a ball"?
 
Black-Balled said:
I have also often wondered about travel ratios post contact.

that is all:wink:
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Travel ratios are very dependent on cut angle. The greater the cut angle, the less energy transferred from the CB to the OB, therefore the CB travels further than it would at a lower cut angle.

But I'm looking at the total distance traveled, i.e. the combined distance of the CB and the OB. I thought cut angle would have no effect on total distance, but Dr. Dave's work shows it has some (although slight for practical purposes IMO).

Ron Swanson said:
Me too. My observation: players who can cue a ball get more energy into the OB than those who cannot. The OB picks up more speed than the CB loses upon contact.
Click to expand...

Bob Jewett said:
I think that is more a belief than an observation. By what percentage do the balls violate Newton's laws for players who can "cue a ball"?
Click to expand...

As per Bob's reply, I don't think the OB knows or cares how well I stroked the CB. It only cares how fast the CB is traveling. (your "good" slow stroke might result in equal speed to my "bad" fast stroke...but the OB isn't judging either one of us).
 
bdorman said:
... But I'm looking at the total distance traveled, i.e. the combined distance of the CB and the OB. I thought cut angle would have no effect on total distance, but Dr. Dave's work shows it has some (although slight for practical purposes IMO).
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The following plot is from one of the links on Dr. Dave's site. It shows the total distance traveled by each ball versus fullness of hit. The left side of the plot is for a very thin hit and the right side of the plot is for a full hit. The blue dotted line is how far the cue ball goes. The solid red line is how far the object ball goes. If you add up the distances on the right, you will see about 40% less total distance than for a thin hit. That seems like it's not slight.

CropperCapture[104].png
 
Bob Jewett said:
The following plot is from one of the links on Dr. Dave's site. It shows the total distance traveled by each ball versus fullness of hit. The left side of the plot is for a very thin hit and the right side of the plot is for a full hit. The blue dotted line is how far the cue ball goes. The solid red line is how far the object ball goes. If you add up the distances on the right, you will see about 40% less total distance than for a thin hit. That seems like it's not slight.
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Am I correct in assuming that "fullness of hit" means "CB/OB overlap", not cut angle?

It appears that there's a significant reduction in change as the fullness of the hit increases (and an increase in change as the hit thins). The difference in total distance traveled between 20% overlap and 40% overlap is 12 (86-74); 40/60 is 7 (74-67); 60/80 is 5 (67-62); and 80/100 is 2 (62-60).



So thicker than a 1/2-ball hit the difference is relatively small...but expect significantly more CB travel with a thin hit which will effect the total distance.
Thanks.
 

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bdorman said:
Am I correct in assuming that "fullness of hit" means "CB/OB overlap", not cut angle?
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That's correct. The horizontal axis is ball-hit fraction.

bdorman said:
It appears that there's a significant reduction in change as the fullness of the hit increases (and an increase in change as the hit thins). The difference in total distance traveled between 20% overlap and 40% overlap is 12 (86-74); 40/60 is 7 (74-67); 60/80 is 5 (67-62); and 80/100 is 2 (62-60).

So thicker than a 1/2-ball hit the difference is relatively small...but expect significantly more CB travel with a thin hit which will effect the total distance.
Thanks.
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Sounds right to me.

Regards,
Dave
 
Ron Swanson said:
You science guys are SUPERB at describing and analysing your own mediocrity. Bravo, fellas. Bravo.

:rolleyes:
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I cannot speak for Ron S but........

There "ain't" nothing mediocre about Bob Jewett and he is for sure a science guy.

And Dr Dave does not appear to do anything in half measure judging by his work.

So what are you trying to say?
 
elvicash said:
I cannot speak for Ron S but........

There "ain't" nothing mediocre about Bob Jewett and he is for sure a science guy.

And Dr Dave does not appear to do anything in half measure judging by his work.

So what are you trying to say?
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I was replying to pj, but, as you raise it, bob jewett and dr dave are hardly pro level players.

Where else would enthusiastic amateurs tell dedicated professionals what they are doing? They are able to demonstrate what THEY are doing.
 
The Southern Law of Physics

The Southern Law of Physics states that:

Less means more and More means less

For some reason its a principle people have a hard time with.....lol
 
Ron Swanson said:
Where else would enthusiastic amateurs tell dedicated professionals what they are doing?
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Two points of clarification:

1) As the original poster, they were replying to me...and I'm certainly not a dedicated professional. My "game" probably doesn't even rank as enthusiastic amateur status.

2) My original question and curiousity is/was for theoretical purposes only. I'm not seeking a practical application, but just the enjoyment of understanding the physics of a game I love.

It's interesting how people jump into a thread, and then assume the thread is all about them. I guess it takes that kind of ego to be a dedicated professional.
 
Distance Calculations

bdorman said:
Two points of clarification:

1) As the original poster, they were replying to me...and I'm certainly not a dedicated professional. My "game" probably doesn't even rank as enthusiastic amateur status.

2) My original question and curiousity is/was for theoretical purposes only. I'm not seeking a practical application, but just the enjoyment of understanding the physics of a game I love.

It's interesting how people jump into a thread, and then assume the thread is all about them. I guess it takes that kind of ego to be a dedicated professional.
Click to expand...

In times past I was doing a study on travel distances off balls at set speeds. Getting the set speed down is the hardest part.

There is a guy on Youtube he calls himself The Oyster that has some interesting stuff on this.

From there can be a lot learned. He plays a lot with what he calls 2 speed with is one length of the table an back again. Perfect lag speed and he uses a mathematical calculation and arrives at very close cue ball placements.

I find the information in Dr. Daves study very useful and as I think on it its hard for one to decide how to best go into practical application of it, which is where I think you leaning. If this is where you are thinking about going, try that guy out and see how you like what hes done. I made a table of sorts and typed it all out somewhere on my computer I will check for it when I get in later.
 
Patrick Johnson said:
He's just lashing out because he's been outed (again) for ignorant bluster. Nothing to bother about - just another Brit with inferiority issues.

pj
chgo
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Lashing out? Lol. You have no idea how restrained i am on here. The odds of Dr Dave & and Bob Jewett trying their hand at selling their wares on, say, TheSnookerForum are identical to that of Stan Shuffett, ie very low indeed.

Ps 'again'? You're going to have refresh my memory, old chap.
 
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