Curvature away from the tangent line

[Colin Colenso]

How about the bottom of the wheels?

Jeff Livingston

I thought about it a bit more and found a real answer...similar to what you said Jeff.

Because the edges of the wheel overhang the rail, this part of the wheel, just behind the point of contact with the track, will move backward relative to the track.

To test this, stick a ruler to the edge of a tube and roll it on a table with ruler over the side. The end of the ruler clearly moves backwards.

 

[Colin Colenso]

This will only work by dividing the scategoriphical nebulas by three astronomical units (AU) and combining the frictional forces to create energy, which powers the cellular respiration of the cueball, which normally takes place in the mitochondrion.

Someone is misunderestimating someone here

 

[chefjeff]

I thought about it a bit more and found a real answer...similar to what you said Jeff.

Because the edges of the wheel overhang the rail, this part of the wheel, just behind the point of contact with the track, will move backward relative to the track.

To test this, stick a ruler to the edge of a tube and roll it on a table with ruler over the side. The end of the ruler clearly moves backwards.

There ya' go...but the reason I speculated it being the bottom of the wheel is because of the Bob's preceding statement:

<snip> it was observed on the Jacksonville tape. With "excess spin" on the cue ball (more than the "unit" spin mentioned above), the bottom of the cue ball is actually moving back towards you on follow shots, and the top of the ball is moving back towards you on draw shots at the instant the ball leaves the tip. Of course, if there is much distance to the object ball, the extra is gone by the collision.

Here is a related puzzle: We see a freight train going sorth down the track at 60 MPH. I say, "There is a part of that train that is always going nouth." What part is that?

Can his statement be true even though a cueball doesn't "overhang the tracks?" With excess follow spin, I suppose it can be true. So if the train's wheels are spinning on the track, as opposed to just rolling, then the bottom of the wheels are moving north. But I like your 'overhanging portion' argument.

BTW, the compass isn't going north, it is just pointing north.

Relativity will come into the discussion here, I reckon. Let's see who else chimes in.

Jeff Livingston

 

[chefjeff]

I asked earlier about the effect on the path from different compositions of the cueball. So, if what Bob said is true...

<snip> As for the original question, draw seems to cause a more dramatic change in the path of the cue ball because for most cases the initial and final paths of the cue ball are separated by a much larger angle -- the cue ball "turns" more with draw. <snip>

...then does a cueball that has easier draw capabilities have a different path than one that is harder to draw? Or is it just the actual backspin on the cueball that matters, not the ease of spinning it? But what if the easier-to-spin cueball can actually spin backward moreso than the other cueballs....does this additional spin capability provide more opportunities for shape than the harder-to-draw cueball?

Jeff Livingston

 

[sjm]

Here is a related puzzle: We see a freight train going sorth down the track at 60 MPH. I say, "There is a part of that train that is always going nouth." What part is that?

OK, Bob, rather than taking the serious approach here, I'll take the comic relief approach.

If the train were crossing either the north or south pole and some of it had crossed and some of it hadn't crossed, then some of that train would be going north and some of it would be going south. Yes, but what if that train isn't passing over one of the two poles? Well, imagine a train track circling the entire earth along any longitudinal line and around the two poles. It would be about 25,000 miles long, the approximate circumference of our planet. A train 15,000 miles long that is traveling along this track would always be over one of the poles, and, therefore, at all times, some of it would be going north and some of it would be going south.

OK, that's enough comic relief for an otherwise highly theoretical thread.

 

[Bob Jewett]

Bob, is the fact that you mispelled both north and south part of the trick to this puzzle somehow, or were those just typos?

I don't make tyops.

 

[Bob Jewett]

...then does a cueball that has easier draw capabilities have a different path than one that is harder to draw? Or is it just the actual backspin on the cueball that matters, not the ease of spinning it? But what if the easier-to-spin cueball can actually spin backward moreso than the other cueballs....does this additional spin capability provide more opportunities for shape than the harder-to-draw cueball?

A light cue ball will not come off at a 90-degree angle from the path of the object ball, but rather back of that line. This means that the paths for both draw and follow are changed. The difference in final angles will be slightly reduced, but I don't think that it will be noticeable.

For the cue ball, the final path is determined by the amount of spin in relation to the speed (and direction) as it comes off the object ball. How well you hit it to get that much spin to arrive at the collision is not important. I think that if a cue ball seems hard to spin to you, it's because it is old and worn and sticky, which makes the spin go off the ball more quickly as it rubs on the cloth, but does not make it harder to get more spin on the cue ball right off the tip.

If the cue ball had its material concentrated in a thin, dense shell, then it would be easier to spin, in that follow and draw would cause a much larger change of angle. (I don't remember how far off center you need to hit an egg-shell sphere to get it to roll smoothly with follow; for a solid ball, it will roll smoothly from the start if you hit it at 70% of its height.) There may be some of this idea coming into play a little with certain cue balls (including the old blue circles, and maybe the new ones?) that had a core of a different, perhaps denser material.

 

[Colin Colenso]

There ya' go...but the reason I speculated it being the bottom of the wheel is because of the Bob's preceding statement:

<snip> it was observed on the Jacksonville tape. With "excess spin" on the cue ball (more than the "unit" spin mentioned above), the bottom of the cue ball is actually moving back towards you on follow shots, and the top of the ball is moving back towards you on draw shots at the instant the ball leaves the tip. Of course, if there is much distance to the object ball, the extra is gone by the collision.

Here is a related puzzle: We see a freight train going sorth down the track at 60 MPH. I say, "There is a part of that train that is always going nouth." What part is that?

Can his statement be true even though a cueball doesn't "overhang the tracks?"

No, the fastest any point of the wheel (non overhanging) moves in the north direction (backwaard) is when directly at the bottom. This part becomes momentaarily still.

Bob is talking about hitting high on a cue ball and overspin is not too hard to get, but doesn't last long. Flick one end of a ruler on a table to make it spin. You'll see the other end moves backward. This is what happens to a cue ball when hit high. The bottom part spins toward the cue...but friction quickly reduces this to rolling spin.

With excess follow spin, I suppose it can be true. So if the train's wheels are spinning on the track, as opposed to just rolling, then the bottom of the wheels are moving north. But I like your 'overhanging portion' argument.

BTW, the compass isn't going north, it is just pointing north.

Relativity will come into the discussion here, I reckon. Let's see who else chimes in.

Jeff Livingston

Yeah...my compass idea was just grasping at straws...and...it ain't a boat, so why a compass

Relativity: If I were running at the speed of light away from the train, then it would appear to be still

 

[Colin Colenso]

A light cue ball will not come off at a 90-degree angle from the path of the object ball, but rather back of that line. This means that the paths for both draw and follow are changed. The difference in final angles will be slightly reduced, but I don't think that it will be noticeable.

In English style pool we play with an undersized cueball. The angles differences are quite noticeable, though the biggest difference is judging distance of follow and draw. The cue ball is about 7-8% lighter. Straight draw is usually played firm just below center as a stun back, as spin back is too hard to judge as it can rocket back. Follows with speed are a nightmare but can create some amazing kiss shots as the cue ball can travel back several inches before curving forward. So you can play shots like this:
START(%Ag8E7%Bg3C9%Cf1D0%P`3F5%Ur9D4%Vh5E6%Wf0E8%Xa3F3%eB4`4%_d6D7%`d0E2%af5E8)END

or this:

START(%Ae1H8%Bg2K4%Ce7M3%Ir5Z4%P]0J2%Ur9D4%Vf0H5%Wc1I1%X^0I9%eB4`4%_p8Y3%`d3P3%ac9H9)END

For the cue ball, the final path is determined by the amount of spin in relation to the speed (and direction) as it comes off the object ball. How well you hit it to get that much spin to arrive at the collision is not important. I think that if a cue ball seems hard to spin to you, it's because it is old and worn and sticky, which makes the spin go off the ball more quickly as it rubs on the cloth, but does not make it harder to get more spin on the cue ball right off the tip.

Also, a sticky or grippy ball, like the old Ivories can affect the friction between the balls on collision. With friction, the object ball basically pulls the cueball forward of the tangent line a little. It will also kill (take) a few percent of the spin off the cueball.

But so called dead balls, or bad compositions do not affect the collision or resultant angles in the way most imagine. The drag on the cloth, as Bob mentioned is the most prevalent factor.

If the cue ball had its material concentrated in a thin, dense shell, then it would be easier to spin, in that follow and draw would cause a much larger change of angle. (I don't remember how far off center you need to hit an egg-shell sphere to get it to roll smoothly with follow; for a solid ball, it will roll smoothly from the start if you hit it at 70% of its height.) There may be some of this idea coming into play a little with certain cue balls (including the old blue circles, and maybe the new ones?) that had a core of a different, perhaps denser material.

Not sure I agree with you here Bob. Or, I should add a twist worth thinking about.

In Discus, big throwers (150-200') use outer weighted discuses as they hold their spin longer against air friction and hence keep flatter in the air. For the average thrower (130') they have less weight to the outside rim, because it makes it easier to spin this way, and they don't need to worry about the spin lasting a couple of extra seconds.

So, the more weight in the shell (outside) the harder it is to create the initial spin. However, an outer weighted cueball will hold its spin better across the friction of the cloth.

So for long power draw shots, a dense outer shell should help. But for shots close to the object ball, a weighted core would allow more spin with less effort.

Note: An outer weighted cueball will roll further, making the table appear faster.

 

[Bob Jewett]

...
So for long power draw shots, a dense outer shell should help. But for shots close to the object ball, a weighted core would allow more spin with less effort..

More spin, maybe, but in the extreme where all the spin is concentrated in the center of the ball, there is no rotational energy in the spin, so the spin cannot make the ball accelerate on the table. The important item here that I did not remember before is the "moment of inertia" for the variously formed spheres. A technical discussion and table of results is available at the Wolfram site. It's not necessary for this discussion to understand all of that, but what is interesting is the table about half-way down that page that lists moments of inertia for various solids.

What does this have to do with cue balls practically?

Well, the only useful part of the table for this discussion is the number in front of "M". For a sphere, that number is 2/5. What does this mean on the table? Well, it says how effective any spin will be in making the ball move. If the cue ball is rolling smoothly on the cloth at speed V, and hits an object ball full, it will accelerate after the hit, and get up to speed 2/7 V (that is 2/(2+5)). One meter per second speed before the hit, goes to 0.28 meters per second after the follow takes. For a hula-hoop, which is a "ring about a perpendicular axis," the final speed would be 1/2 V or 50% of the initial rolling velocity. This large number is part of why it is easy to do snap-back tricks with spinning hoops.

For a spherical shell, the number in front of M is 2/3, so the final follow velocity would be 40% of the initial incoming velocity. (Take 2/3 and change it to 2/(2+3) = 2/5 = 0.40) An egg-shell ball would follow pretty well. Another consideration is how much the object ball would slow down if it were a shell. It would start out with V and then slow to 60% of that speed. A normal object ball slows to 5/7 of its initial speed as it acquires normal roll, or 71%.

The extreme in the other direction would be with the weight all in a tiny core. In that case, the "M" number is 0, the object ball does not slow down, and the cue ball sits in place regardless of spin. Such balls don't exist, of course, but there are balls with slightly weighted centers.

 

[Colin Colenso]

More spin, maybe, but in the extreme where all the spin is concentrated in the center of the ball, there is no rotational energy in the spin, so the spin cannot make the ball accelerate on the table. The important item here that I did not remember before is the "moment of inertia" for the variously formed spheres. A technical discussion and table of results is available at the Wolfram site. It's not necessary for this discussion to understand all of that, but what is interesting is the table about half-way down that page that lists moments of inertia for various solids.

What does this have to do with cue balls practically?

Well, the only useful part of the table for this discussion is the number in front of "M". For a sphere, that number is 2/5. What does this mean on the table? Well, it says how effective any spin will be in making the ball move. If the cue ball is rolling smoothly on the cloth at speed V, and hits an object ball full, it will accelerate after the hit, and get up to speed 2/7 V (that is 2/(2+5)). One meter per second speed before the hit, goes to 0.28 meters per second after the follow takes. For a hula-hoop, which is a "ring about a perpendicular axis," the final speed would be 1/2 V or 50% of the initial rolling velocity. This large number is part of why it is easy to do snap-back tricks with spinning hoops.

For a spherical shell, the number in front of M is 2/3, so the final follow velocity would be 40% of the initial incoming velocity. (Take 2/3 and change it to 2/(2+3) = 2/5 = 0.40) An egg-shell ball would follow pretty well. Another consideration is how much the object ball would slow down if it were a shell. It would start out with V and then slow to 60% of that speed. A normal object ball slows to 5/7 of its initial speed as it acquires normal roll, or 71%.

The extreme in the other direction would be with the weight all in a tiny core. In that case, the "M" number is 0, the object ball does not slow down, and the cue ball sits in place regardless of spin. Such balls don't exist, of course, but there are balls with slightly weighted centers.

Very interesting Bob, it would be a lot of fun playing with some balls that approximated those properties

With the shell cue ball, off center hits would feel weightier and harder to create high spin rates. Center struck balls would slow significantly as the topspin roll took effect. Drag shots would slow very dramatically.

Making up your own set with various weight distribution characteristics (known only to yourself) would be a huge advantage if you practiced to accommodate. That is, in a challenge match. It would drive the opponent crazy and you could pull out the scales and show that the balls are all the correct weight. lol

 

[Colin Colenso]

Bob, don't run away without posting your answer to the sorth, nouth train proposition. We're in suspenders.

 

[chefjeff]

Very interesting Bob, it would be a lot of fun playing with some balls that approximated those properties

With the shell cue ball, off center hits would feel weightier and harder to create high spin rates. Center struck balls would slow significantly as the topspin roll took effect. Drag shots would slow very dramatically.

Making up your own set with various weight distribution characteristics (known only to yourself) would be a huge advantage if you practiced to accommodate. That is, in a challenge match. It would drive the opponent crazy and you could pull out the scales and show that the balls are all the correct weight. lol

This is all great, guys, and thanks...

...now, can you tell me how to use this info in the real world of various cueballs? i.e., can you approximate which of today's most popular cueballs would be prone toward what behaviors?---you know, so I can actually manage some shots using this info.

Oh crap...it's late...If I don't get the house cleaned before my wife gets home from work, I'm dead!

Later,

Jeff Livingston

 

[Bob Jewett]

...now, can you tell me how to use this info in the real world of various cueballs? i.e., can you approximate which of today's most popular cueballs would be prone toward what behaviors?---you know, so I can actually manage some shots using this info.

Well, in practice the ideas about funny weight distributions are not useful. Cue balls may be slightly center-weighted, but it can't be very dramatic, since the majority of the ball still has to be cast phenolic.

What is important to take away from this discusion is that cue balls can vary in weight and surface properties, and those two things can make a huge difference in how position works. I remember when I was in the military and played for hours a day in the rec room. I thought I was pretty good, and could draw the cue ball up my sleeve. What I didn't realize was that the cue balls were all very small, and drew far more easily than standard balls. The test came when I got up a little courage and money and went into town to play at the local pool hall. The cue ball was huge compared to what I was used to, and had a surface that looked like it had been sanded. None of my draw shots worked as expected, so I had no position play. The local I was playing saw this, and just knocked the balls around (at nine ball) until it got down to the seven or eight and then he would clear the table. The funny part is that I saw what he was doing during the game, but still thought I could start playing better.

I think it is important to get experience with a variety of equipment if you are going to be playing under a variety of conditions.

Mosconi was known for carrying around his own set of clean, polished balls for exhibitions, and I think he did that for a reason.

 

[Colin Colenso]

This is all great, guys, and thanks...

...now, can you tell me how to use this info in the real world of various cueballs? i.e., can you approximate which of today's most popular cueballs would be prone toward what behaviors?---you know, so I can actually manage some shots using this info.

Oh crap...it's late...If I don't get the house cleaned before my wife gets home from work, I'm dead!

Later,

Jeff Livingston

In addition to this knowledge assisting with adapting to table conditions, it can be very useful in constructing challenging shots in games.

8-ball in particular is a game where creative cannons, combinations and masse's come in handy and present game winning situations. I find an opportunity for a creative shot, that turns a game about one in three games.

Such shots often intimidate an opponent and puts pressure on their defensive game.

 

[drivermaker]

Laura...do you see what you've started here? As a two year player, you already have waaaaay to much shit rolling around in your head, and I do specifically mean SHIT! I've gotten the impression that you want to learn this game from the physics side first, and not just from this thread. What you need to learn is how to make balls, and then more balls, and even more balls without missing by getting on the table for 6 hours a day (and you can) and just OBSERVING what the CB does and where it goes after striking the OB, with or without some english and at various speeds. You're thinking about deflection, contact induced throw, curvature, parabolas, skid, and every phenomenon known to man and it's muddling your brain. Get those aiming systems that you were introduced to down pat, make balls, and watch what the hell is happening.
PUT THE TIME IN AT THE TABLE!