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View Full Version : Physics factoid: Reflections in a cue ball

12-21-2006, 12:12 PM
This may not be of any practical significance, but I did observe an interesting phenonemon regarding my Rempke traing cue ball, that would probably apply to other highly polished billiard balls as well. It is probably only of interest to students of physics as applied to pool.

This cue ball has the light reflection properties of a hemispherical convex mirror. If you place a point source of light at a distance from the cue ball, the "image" of the light as seen on the cue ball will be:
1. upright
2. "minified"
3. always located halfway along the radius from the center of the ball to the surface of the ball, along the line connecting the center of the ball to the point source.

This can be tested using a cheap LED flashlight placed a few feet away, at a height of 1 1/8 inches. The flashlight does not have to be pointed directly at the cue ball, just in the general direction. The LEDs used in these flashlights have a blue tint that distinguishes them from other lights in the room.

For the Rempke ball, this has some interesting implications, because the markings on the ball allow perfect orientation to the point source of light. This is because the outermost "black circles" happen to be at half radius. When the ball is oriented as follows, the two marked center spots on the Rempke ball will align with the point source, meaning that a square hit will deposit the ball on the light source.
1. Looking straight down on the cue ball, rotate the ball until the "image" of the point source appears at the intersection of the outer black circle and one of it's intersecting perpendicular lines.
or
2. Looking at the ball from the side, the image and largest black circle should superimpose when the center spots are aligned to the source.
3. When viewed from the source, the reflection should be dead center.

I played around with this as an aiming system. Placing the light source at the center point of the ghost ball, and then rotating the cue ball so that the image of the light was in the positions described above. This would position the cue ball so that a dead-on hit applied to the center point target on the Rempke would result in the center of the ball hitting the light source.It does indeed work, but is subject to being able to get the cue ball to hold perfectly steady, and ultimately proved more work than practical for routine use.

I just put this observation out there in case someone can find a practical application for it.

dr_dave
12-21-2006, 04:43 PM
<blockquote><font class="small">Quote DeadCrab:</font><hr> This may not be of any practical significance, but I did observe an interesting phenonemon regarding my Rempke traing cue ball, that would probably apply to other highly polished billiard balls as well. It is probably only of interest to students of physics as applied to pool.

This cue ball has the light reflection properties of a hemispherical convex mirror. If you place a point source of light at a distance from the cue ball, the "image" of the light as seen on the cue ball will be:
1. upright
2. "minified"
3. always located halfway along the radius from the center of the ball to the surface of the ball, along the line connecting the center of the ball to the point source.

This can be tested using a cheap LED flashlight placed a few feet away, at a height of 1 1/8 inches. The flashlight does not have to be pointed directly at the cue ball, just in the general direction. The LEDs used in these flashlights have a blue tint that distinguishes them from other lights in the room.

For the Rempke ball, this has some interesting implications, because the markings on the ball allow perfect orientation to the point source of light. This is because the outermost "black circles" happen to be at half radius. When the ball is oriented as follows, the two marked center spots on the Rempke ball will align with the point source, meaning that a square hit will deposit the ball on the light source.
1. Looking straight down on the cue ball, rotate the ball until the "image" of the point source appears at the intersection of the outer black circle and one of it's intersecting perpendicular lines.
or
2. Looking at the ball from the side, the image and largest black circle should superimpose when the center spots are aligned to the source.
3. When viewed from the source, the reflection should be dead center.

I played around with this as an aiming system. Placing the light source at the center point of the ghost ball, and then rotating the cue ball so that the image of the light was in the positions described above. This would position the cue ball so that a dead-on hit applied to the center point target on the Rempke would result in the center of the ball hitting the light source.It does indeed work, but is subject to being able to get the cue ball to hold perfectly steady, and ultimately proved more work than practical for routine use.

I just put this observation out there in case someone can find a practical application for it. <hr /></blockquote>

Thank you for sharing that. Maybe not very useful, but interesting anyway.

Dave

cushioncrawler
12-21-2006, 05:51 PM
One of my old billiardz mates called me over to hiz (12') table one day -- the red woz on The Spot, and the qball woz dead in line to pot the red in a corner pocket. He said that he had been having trouble with dead straight pots, but that he had found a trick to help.

He pointed out that u could see the reflection of the qball on the red -- it woz very small, and difficult to see at first. He said that he simply aimed the cue throo the qball and throo the reflected qball.

Hiz trick wouldnt be any good to me. But anyhow, it reminded me that the modern hi-gloss krapamith (light &amp; soft &amp; hi-gloss) would have been illegal in the oldendayz (but for other reasons). The old Crystalates and Bonzolinez (killed in about 1973) were low-gloss, ie zero reflection. madMac.

Cornerman
12-22-2006, 08:32 AM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote DeadCrab:</font><hr>

This cue ball has the light reflection properties of a hemispherical convex mirror. If you place a point source of light at a distance from the cue ball, the "image" of the light as seen on the cue ball will be:
1. upright
2. "minified"
3. always located halfway along the radius from the center of the ball to the surface of the ball, along the line connecting the center of the ball to the point source.
<hr /></blockquote>

Thank you for sharing that. Maybe not very useful, but interesting anyway.

Dave <hr /></blockquote> Many of the "points of light" aiming systems are based on these reflections.

Fred

Fran Crimi
12-22-2006, 08:47 AM
I would think that placing a light source at a particular spot for the sole purpose of aiming would be considered cheating. That would be marking, wouldn't it?

Fran

Deeman3
12-22-2006, 09:16 AM
<blockquote><font class="small">Quote Fran Crimi:</font><hr> I would think that placing a light source at a particular spot for the sole purpose of aiming would be considered cheating. That would be marking, wouldn't it?

<font color="blue"> Naw, many of the old timers used to "shoot the lights" and I believe you would have to physically place something on the ball to cheat. JMO

DeeMan </font color>

<hr /></blockquote>

Fran Crimi
12-22-2006, 12:47 PM
Deeman, don't confuse reflections that are already there with reflections specifically placed by positioning lights a certain way for the sole purpose of aiming. That's a different story and I'm pretty sure that would be considered marking.

Fran

12-22-2006, 03:04 PM
I was thinking of using the method for an aiming/banking trainer in conjunction with the Rempke ball.

I don't think it would be appropriate for any contests of skill.

I had been experimenting with aligning the Rempke pall perfectly so that a novice player could concentrate on practicing stroke and square cue ball hit without having to worry about distant aim.

cushioncrawler
12-22-2006, 03:50 PM
<blockquote><font class="small">Quote DeadCrab:</font><hr> .....I had been experimenting with aligning the Rempke pall perfectly so that a novice player could concentrate on practicing stroke and square cue ball hit without having to worry about distant aim....<hr /></blockquote>
Hmmmm -- I reckon that no-one can align anything perfectly -- the eyes allwayz lie. I think that even if u only used one eye (closing the other), the rempe ball wouldnt be aligned much better. I think that even if u only had one eye from birth, u wouldnt be able to align the rempe ball perfectly.

In fact i wonder whether a marked training ball (qball) ever does anyone any good, in any way -- i mean, better than uzing a plain qball. Or even uzing it for an objectball. madMac.

Fran Crimi
12-23-2006, 07:30 AM
Mac, I don't think a training ball would appeal to everyone but it would probably appeal to some. People learn in different ways. Some are content to shoot shots over and over with more emphasis on feel and less on visual; others prefer a more specific visual approach.

Fran

Fran Crimi
12-23-2006, 07:37 AM
I'm not sure why you would need both the reflections and the markings on the Rempe ball. Wouldn't one or the other be sufficient for training purposes? Maybe you could create your own training system just with reflections.

Fran

wolfdancer
12-23-2006, 10:51 AM
http://regentsprep.org/Regents/Math/coreflec/redpep.gif
Since everything is reversed in a reflection....wouldn't you end up shooting into the opposite pocket?
web page (http://regentsprep.org/Regents/Math/reflect/Lreflect.htm)

"ZZZZZZ"

I was given a Rempe cue ball, and not wanting to break the chain and have 7 yrs of missed balls, gave it away immediately after deciding it wouldn't make a good paperweight (it rolled off)

Jal
12-23-2006, 12:36 PM
<blockquote><font class="small">Quote wolfdancer:</font><hr>Since everything is reversed in a reflection....<hr /></blockquote>When did this start happening?

Jim &lt;-- hoping it means he's been shaving his feet all along

cushioncrawler
12-23-2006, 02:16 PM
<blockquote><font class="small">Quote Fran Crimi:</font><hr> Mac, I don't think a training ball would appeal to everyone but it would probably appeal to some. People learn in different ways. Some are content to shoot shots over and over with more emphasis on feel and less on visual; others prefer a more specific visual approach..... <hr /></blockquote>
Hi Fran -- I allways like to start a session by hitting a hi-number pool ball straight up the table, with the stripe vertical and aligned up the table -- firstly i make a chalk mark on the top cushion and one at my end the exact same distance from the side cushion -- if the qball (poolball) has some wobble on the way up, or if it misses the chalk mark on the top cushion, or if it comes off the cushion at other than 90dg, then i know that my cueing isnt on line, or that i arent hitting the qball dead center, or something.

But, i am allways aware that the stripe on the poolball shood make it eezyr for me to aim and hit dead center on the qball, and that the little routine that i described duznt help me to find and hit the dead center of a plain qball, ie a marked ball is too flattering. But as soon as i am hitting well enuff with the striped qball, i throw it away and do the same routine with a plain qball. Some of my striped qballs have an off-center stripe, so i have to be carefull to use a "good" one.

And, more on-topic, i am aware that when i align the striped qball with the chalk mark on the top cushion, it might look aligned but it usually iznt as good as i think. But i have never made a study of this.

I have made a bit of a study of a similar sort. I ask different guys to place the qball dead in line with an object ball to set up a dead straight pot for a corner pocket. Everyone allways places the qball off line, sometimes a little off line, sometimes a lot, allwayz.

Fran Crimi
12-23-2006, 08:25 PM
Yup. I've also found that what we see isn't necessarily what reality is, and it becomes more prominent as we try to focus on something very small, such as a point on a ball. Combine that with the different ways in which people absorb information and we have a very diverse group of people, all trying to accomplish the same thing but in different realities...Yikes...no wonder why teaching is hard.

Fran

Qtec
12-23-2006, 10:38 PM
If a player who alligns wrong makes the shot 99% of the time, is there a problem? It doesn't matter what you see as long as you see as the same every time.
IMO, this is the biggest problem with systems, because we all see things differently, they can never work. They might be technically correct but they don't take into account individuals. ie one man's 1/2 ball is another man's 3/4 ball!
Q

cushioncrawler
12-24-2006, 02:54 AM
<blockquote><font class="small">Quote Qtec:</font><hr> If a player who alligns wrong makes the shot 99% of the time, is there a problem? It doesn't matter what you see as long as you see as the same every time.
IMO, this is the biggest problem with systems, because we all see things differently, they can never work. They might be technically correct but they don't take into account individuals. ie one man's 1/2 ball is another man's 3/4 ball!... <hr /></blockquote>
For sure. I remember checking the alignment of the Ozzy snooker champ (and he was the billiards champ at that time allso). When he had a dead straight shot, he aimed as if to hit right of center on the qball, and he aimed as if to shoot right of center on the object ball, but the OB would enter the pocket without touching the sides. But he could never get within 6" of getting the qball to follow the OB into the pocket (this is a praktis routine) -- he put so much unintentional swerv and spin on the qball, that it could never follow straight throo. For most of us, even champions, 4 "wrongs" can make a "correct".