BHE and low deflection shafts

[Colin Colenso]

QUOTE=Jal]Jaden, I meant to comment on your diagram. I fear that it's not what's generally accepted as taking place, though it's an interesting alternative. It's usually imagined that the shaft bends in the other direction: to the left for left english; to the right for right english. I think the high-speed videos support this.

If, for instance, you were applying left english and the shaft was bowing to the right, the force acting on cue at the tip would have to be pointing a little to the right. Otherwise the cue wouldn't bend in that direction. The cueball would experience the same force, though in the opposite direction (action/reaction), and would be propelled to the left of the aiming line. You would get, in effect, negative squirt.

That's the orthodox view, but you're welcome to topple it if you can.

Edit: But we're talking about the overall average direction of the force here. I wouldn't be surprised, in fact it seems almost necessary (to me), that what your describing does take place at the beginning of impact. This might/should contribute an element of negative squirt, until ball rotation takes over and changes the direction of the initial force.


Jim

It would have to take place. attached is an image illustrating the forces and where they apply to the shaft and because of that, why it would have to bend in that direction
View attachment 40201

If you look at the drawing you will see thatthe blue line represents the center of mass of the CB and the straight red line represents the contact point on the tip and line of direction of force to the shaft.

The curved red line represents the parabolic(rough representation) curve of force from the point of majority of mass in the CB and the point of contact on the tip. That line of force should always cause initial bend to be to the opposite side of the line of force compared to center line throughout the time of contact. After contact doesn't matter.

Regardless of how it's described, the same thing is happening. The Cueball is going in the direction where the majority of mass directs it. If you line up on the centerline and stroke off center the center of mass of the CB is still pointing straight ahead from the original aimline. [/QUOTE]

Jaden,

This doesn't look like what is going on to me. For one thing, there cannot be parabolic curves of force. A force is a linear vector, though there can be many independent forces contributing.

Where I think you may be going wrong here is thinking that the CB opposes the cue's force through its center of mass, creating a force outside the line of the cue. But this only happens if the collision is elastic (slipping).

I've argued before that there is a small degree of slipping, perhaps in the 0.1 to 1% range and this has some effects, but essentially the collision is the same as it would be if a chunk of the cue ball were cut out so that the cue tip collided with a face at 90 degrees.

This type of collision would also create the rotation which would push sideways against the cue tip, explaining much of, if not all the squirt.

If the cue did in fact bow back, I can't see any reason why it wouldn't push back in a straight line, that is opposite the forces directed at it. So the key I think is identifying the forces being exerted onto the cue by the CB.

Hope that makes sense.

Colin

 

[Jaden]

It would have to take place. attached is an image illustrating the forces and where they apply to the shaft and because of that, why it would have to bend in that direction
View attachment 40201

If you look at the drawing you will see thatthe blue line represents the center of mass of the CB and the straight red line represents the contact point on the tip and line of direction of force to the shaft.

The curved red line represents the parabolic(rough representation) curve of force from the point of majority of mass in the CB and the point of contact on the tip. That line of force should always cause initial bend to be to the opposite side of the line of force compared to center line throughout the time of contact. After contact doesn't matter.

Regardless of how it's described, the same thing is happening. The Cueball is going in the direction where the majority of mass directs it. If you line up on the centerline and stroke off center the center of mass of the CB is still pointing straight ahead from the original aimline.

Jaden,

This doesn't look like what is going on to me. For one thing, there cannot be parabolic curves of force. A force is a linear vector, though there can be many independent forces contributing.

Where I think you may be going wrong here is thinking that the CB opposes the cue's force through its center of mass, creating a force outside the line of the cue. But this only happens if the collision is elastic (slipping).

I've argued before that there is a small degree of slipping, perhaps in the 0.1 to 1% range and this has some effects, but essentially the collision is the same as it would be if a chunk of the cue ball were cut out so that the cue tip collided with a face at 90 degrees.

This type of collision would also create the rotation which would push sideways against the cue tip, explaining much of, if not all the squirt.

If the cue did in fact bow back, I can't see any reason why it wouldn't push back in a straight line, that is opposite the forces directed at it. So the key I think is identifying the forces being exerted onto the cue by the CB.

Hope that makes sense.

Colin[/QUOTE]

I've missed a lot of the disagreements that we;ve had in the past, because most of the time it is just a misunderstanding of terms because I come from a background of applied physics as opposed to official physics. I don't mean applied physics in the traditional term. I n fact I'm saying exactly that I don't use the official terms and that is the main difference.

What I meant when I said a parabolic curve of force is the way that force travels through a flexible object like a shaft if the force being applied is off center the flesing of the shaft occurs in a parabolic curve from the point of applied force to the place of force equality of ditribution opposite the side when compared to center line of the flexible object.
Take a piece of paper and apply pressure linearly to one side length ways and you'll see by the way it bends what I'm referring to.

In my diagram, I'm showing that the mass of the cue ball that is being pushed is off to the right of the shaft when left english is applied and the point of contact is off center line to the right. This would cause the line of force to be a parabolic line of force radiating to the opposite side of the shaft or curving to the left.

 

[Jaden]

It would have to take place. attached is an image illustrating the forces and where they apply to the shaft and because of that, why it would have to bend in that direction
View attachment 40201

If you look at the drawing you will see thatthe blue line represents the center of mass of the CB and the straight red line represents the contact point on the tip and line of direction of force to the shaft.

The curved red line represents the parabolic(rough representation) curve of force from the point of majority of mass in the CB and the point of contact on the tip. That line of force should always cause initial bend to be to the opposite side of the line of force compared to center line throughout the time of contact. After contact doesn't matter.

Regardless of how it's described, the same thing is happening. The Cueball is going in the direction where the majority of mass directs it. If you line up on the centerline and stroke off center the center of mass of the CB is still pointing straight ahead from the original aimline.

Jaden,

This doesn't look like what is going on to me. For one thing, there cannot be parabolic curves of force. A force is a linear vector, though there can be many independent forces contributing.

Where I think you may be going wrong here is thinking that the CB opposes the cue's force through its center of mass, creating a force outside the line of the cue. But this only happens if the collision is elastic (slipping).

I've argued before that there is a small degree of slipping, perhaps in the 0.1 to 1% range and this has some effects, but essentially the collision is the same as it would be if a chunk of the cue ball were cut out so that the cue tip collided with a face at 90 degrees.

This type of collision would also create the rotation which would push sideways against the cue tip, explaining much of, if not all the squirt.

If the cue did in fact bow back, I can't see any reason why it wouldn't push back in a straight line, that is opposite the forces directed at it. So the key I think is identifying the forces being exerted onto the cue by the CB.

Hope that makes sense.

Colin[/QUOTE]

I've missed a lot of the disagreements that we;ve had in the past, because most of the time it is just a misunderstanding of terms because I come from a background of applied physics as opposed to official physics. I don't mean applied physics in the traditional term. I n fact I'm saying exactly that I don't use the official terms and that is the main difference.

What I meant when I said a parabolic curve of force is the way that force travels through a flexible object like a shaft if the force being applied is off center the flesing of the shaft occurs in a parabolic curve from the point of applied force to the place of force equality of ditribution opposite the side when compared to center line of the flexible object.
Take a piece of paper and apply pressure linearly to one side length ways and you'll see by the way it bends what I'm referring to.

In my diagram, I'm showing that the mass of the cue ball that is being pushed is off to the right of the shaft when left english is applied and the point of contact is off center line to the right. This would cause the line of force to be a parabolic line of force radiating to the opposite side of the shaft or curving to the left.

 

[Jal]

I put an object ball on the head spot and put another about 1mm away from it and lined up as best I possibly could (with wife on at the foot rail trying to help me line things up) to be aimed at the foot spot.

Shooting at about a 45 degree angle from the right side, with dry ob's, the ball on the spot was thrown about 1 ball width to the left of the bottom diamond, on each of 4 attempts.

After wetting the contact points with saliva on both ob's I got a result that really puzzles me. The ob contacted the foot rail about 1 ball width (or a little less than a ball width) to the other side/the right side of the middle diamond on the foot rail. Negative throw (??); for lack of a better term. What happened? The aim was not off, I checked that VERY carefuly and was backed up by the wife observing from the foot rail. I'm at a loss.

Jim. my thanks to you and your wife for taking the time to perform these tests.

There is an explanation for the result you got with the wetted balls. For one thing, the 1 mm separation makes for a little bit of a cut angle between the first and second balls (about 1 degree at a 45 degree approach angle). Also, the balls are in contact for a certain amount of time as they compress, and this adds a small amount to the cut angle too - about 1/2 degree or so depending on how hard you were shooting.

All in all, it looks like wetting did virtually eliminate throw. Thanks again for checking this out.

Jim

 

[Jal]

I used the Predator w/BHE. I placed a wetted ob on the center spot and the cb on the head spot. I used a minimum of 2 tips of BHE w/the Predator, hitting firm speed (in trail shots the cb traveled to the end rail, head rail, end rail and back to center table = 3.25 table lengths) and a pivot point of 12". After 12 shots the most usual action was for the ob to hit the end rail from 1/2 to 1 ball to the right of the bottom rail diamond.

I also hit several shots w/parallel english with the most common result being the ob hitting the bottom rail about 3/4 to 1 ball widths to the right of the center diamond

For the sake of comparison: I then hit the same shot w/a dry ob and the result was hitting the bottom rail about 2 to 3 ball widths right of the center foot diamond usually banking the ball into the head right pocket, sometimes just to the short rail side of the pocket and sometimes hitting the long rail coming in. It was hard to see exactly where on the bottom rail the ob was hitting (wife not available for this test) but the most common result was for the ob to hit the front short rail about 1 to 1.5 ball widths short of banking into pocket. I think this equated to hitting the bottom rail about 2 ball widths to the right of the center diamond.

I'm learning that throw makes significantly more difference than I'd imagined. Now that I know how to use BHE w/my playing cue I've been practicing to see how much throw affects my attempts to pot balls and I'm finding out why, on many occasions, I've been missing. I don't know where I got the idea but I had it in my head that throw only affected balls shot at very slow speeds. WRONG!

Went back to the table and hit about 40 shots w/my Sailor play cue using the above methods w/dry ob and BHE and the pivot point where I learned yesterday it should be. The ob most frequently impacted the bottom cushion about 1 ball width right of the center diamond.

Again my thanks. If I can do something for you, let me know.

It's tough to tell where the pivot point is located on your cue. It would help greatly if instead of using a fixed pivot loacation of 12", that you vary it until the object ball takes off as perfectly straight as possibles (ie, along the line joining the center of the cueball and object ball before the shot is made). This can be very awkward if the cue's intrinsic pivot point is far from the tip, but trying to calculate from the object ball's direction is very inaccurate. It would be interesting to know if it was, say, at least greater than 20-30" from the tip, as your earlier trials seem to indicate.

Also, from your results, it looks that swerve is affecting them somewhat. The balls need to be only about a diamond apart with a hard hit to get rid of this.

Again, I don't expect anything, but would be interested in the results of any further testing you do. Please thank your wife too.

Jim

 

[Jal]

... The main problem was that it relies entirely on the rotation/deflection mechanism as the sole cause of squirt. ( i.e. As the CB tries to rotate due to the spin, it much push against the tip that is spinning it such that with right english, the CB pushes the tip to the right, and hence bounces off slightly to the left...squirting ).

If this was the only mechanism for squirt, then speed maybe shouldn't come into it. That's why I proposed the 'partial tip slipping' mechanism as a minor but significant contributor to squirt.

Colin, I certainly don't know if slip is taking place. But an increase in speed should have the tip and ball rotating a little longer together, thus slightly increasing the average tip offset. This should produce a little greater spin/speed ratio and a little more squirt...but not much. Perhaps testing with the same cueball under different surface conditions would reveal whether slip is a significant component?

...I did originally think that these long pivot points were due to misinterpreting the role of throw, but some calculations I did showed me such innacuracies shouldn't change pivot point estimation by more than a few inches.

That's good to hear because that's what my calculations indicated too! Post-impact swerve can explain more of it, but I don't think all of it, unless people are elevating their cues much more than I would expect.

The only explanation I can offer is that they are perhaps playing the shots too slowly such that swerve in addition to the throw, it giving the appearance of much longer pivot points.

Quite possibly. And maybe in addition to this, some swerve is taking effect sooner than expected since the cueball is being driven downward into the cloth somewhat.

They do appear to use a different testing method than I do by playing the CB onto an OB that is not too far away and tracking the OB.

I just aim at points or balls several feet away. What I do know for sure is that pivoting at over 20" with a predator on a very firm shot with BHE will send the CB about 1/2" wide of the target contact point on the OB, over 4 feet of travel. In other words, not even close. But if I play the same shot at slow speed, the swerve will make it pretty close.

From an aficionado of BHE as yourself, this strongly suggests that the pivot point is as you indicated earlier, well within 20" of the tip. But, we shall see, since the 30-50" contingent are no slouches either.

Jim

 

[Jal]

I've missed a lot of the disagreements that we;ve had in the past, because most of the time it is just a misunderstanding of terms because I come from a background of applied physics as opposed to official physics. I don't mean applied physics in the traditional term. I n fact I'm saying exactly that I don't use the official terms and that is the main difference.

What I meant when I said a parabolic curve of force is the way that force travels through a flexible object like a shaft if the force being applied is off center the flesing of the shaft occurs in a parabolic curve from the point of applied force to the place of force equality of ditribution opposite the side when compared to center line of the flexible object.
Take a piece of paper and apply pressure linearly to one side length ways and you'll see by the way it bends what I'm referring to.

In my diagram, I'm showing that the mass of the cue ball that is being pushed is off to the right of the shaft when left english is applied and the point of contact is off center line to the right. This would cause the line of force to be a parabolic line of force radiating to the opposite side of the shaft or curving to the left.

Jaden, this is how I think the forces should be viewed. The black arrows are the main (net) force and its components acting on the cueball. The red arrows are the reaction force and components acting on the stick. These are equal in magnitude but opposite in direction to the black ones.

Your model seems to leave out or minimize the tangential component. The sum of the tangential and normal components yield the net force which would point straight ahead in the ideal case. However, ball rotation (perhaps with a touch of slip), diminishes the tangential component a little. This reduced component, when added to the normal one, makes the net force point slightly toward the center of the cueball, causing squirt.

Since the red reaction force is pointing slightly to the left, that's the direction in which the stick will bend.

Jim

 

[Joe T]

Hi Guys,

I just received a message asking me to look over this thread and I did, really I kinda skimmed so if I repeat anything please forgive but you can point it out to me if you like.

I can't hang with some of the techinical experts in this thread so I'll just offer my thoughts that I think may help some players get to the end result.

First off I believe there's 3 decent ways to apply side spin and then theres parallel which I think stinks.

#1 Simple BHE, just aiming and moving the backhand in or out. One thing about this method that is never or hardly ever mentioned that drives me nuts is this; Sometimes when players do this they actually change their aim off to the side of the intended english and then squirt helps them make the ball and that's why some people can't use the predator and make the ball. I know it might be hard to understand but when I pivot over I am changing the aim or angle of the stick BUT I am not changing the aim line and that's why I can aim center to center then pivot and stop the ball spinning with the Z shaft.

#2 front hand pivot, just aim it up, keep your back hand still and adjust your bridge to the desired tip position. You have to be careful not to slide your backhand over in the same direction cuz now you're coming close to adding a bit of parallel and that'll cause you more squirt.

#3 A little of both, which I like to do when I'm playing. You use a little movement in the bridgehand (to the right for right spin and left for left, obviously) and then a little in the backhand in the opposite direction (backhand goes left for right spin and vice versa)

Most current pros do not usually aim center and then pivot but they do fall on the shots with their sticks angled off and if you were to ask them to stop after they set up to the shot you would probably be able to move the butt of their cue in or out and their tip would be very close to center ball and set on the aim line. They can do this because of years of learning that angle that they fall on the shot with. You can speed up your learning process by first aiming center and then pivoting over to that angle and once that has been accomplished you may choose to simply fall on the shots with your stick angled off also. I've played both ways and can tell you when under extreme pressure I prefer to fall on the aim line with center (because that requires less feel or guess work) and then pivot to apply my english. BUT when playing and in stroke you may find me simply walking into the shots with the side spin already applied, skipping the center ball step.

I recommend no matter what cue you use that you become and expert at setting up straight in shots and start applying all the different tip positions you'll be using in the game. If you can't do it on straight in shots you're leaving a lot to luck on all your other shots. Use at least the 3 methods I suggested and see which one feels the best to you and which one you think you can master. It's an area that needs to be mastered if you have plans of playing at a decent level. You need spin and you need to be confident and consistent when using it.

 

[PKM]

So do a lot of pros and good players use BHE, or is parallel more common?

 

[jsp]

Jaden, this is how I think the forces should be viewed. The black arrows are the main (net) force and its components acting on the cueball. The red arrows are the reaction force and components acting on the stick. These are equal in magnitude but opposite in direction to the black ones.

Your model seems to leave out or minimize the tangential component. The sum of the tangential and normal components yield the net force which would point straight ahead in the ideal case. However, ball rotation (perhaps with a touch of slip), diminishes the tangential component a little. This reduced component, when added to the normal one, makes the net force point slightly toward the center of the cueball, causing squirt.

Since the red reaction force is pointing slightly to the left, that's the direction in which the stick will bend.

Jim

Jal, great diagram. I've always wanted to draw that same diagram myself and post it, but just never got the time. But since you did already, I want to bring up a nagging question that has always bothered me whenever I read physics papers on squirt. Maybe you can help me out.

Looking at your diagram, you can break up the net force of the cue in its tangential component and its normal component. Essentially, the net force is the summation of these two forces, correct?

If you just examine the tangential force component without the normal component, then the CB would spin as the result of this force. However, the CB wouldn't go anywhere because there is no normal force to move its center of mass. Essentially, the CB would just spin like a top.

If you just examine the normal force component without the tangential component, then the CB would accelerate in the direction pointed by the normal vector. However, the CB would have no spin because there is no tangential force.

Again, the net force is the summation of the tangential force and the normal force. So if you want to find out the resulting spin and direction of the CB experienced by the net force, can you not just superpose the above results? Wouldn't that mean the CB would have some spin and that it would depart in the normal direction?

The direction of the CB is what I want to focus on, because that's not what you would expect, nor that is what you see in real life. What you see is that the CB departs in the direction very close to vertical. But if you break down the problem in the way that I described above, this is the result that you get. So my question is...what is wrong with my analysis? Can I not break up the net force to its tangential and normal components and combine the results?

 

[jsp]

To attempt to answer my own question, I believe the reason why you don't see the CB departing in the normal direction in real life is because of the finite impact time between the CB and cue tip. In other words, the force exerted by the cue is not a pure impulse force, where the time duration of the force approaches zero.

Because of the impact time is non-zero, the tip has time to drag the CB in the vertical direction before the CB has the chance to totally depart in the normal direction.

But this is just a guess. Any ideas?

 

[Caromsoft]

Hi Guys,

I just received a message asking me to look over this thread and I did, really I kinda skimmed so if I repeat anything please forgive but you can point it out to me if you like.

I can't hang with some of the techinical experts in this thread so I'll just offer my thoughts that I think may help some players get to the end result.

First off I believe there's 3 decent ways to apply side spin and then theres parallel which I think stinks.

#1 Simple BHE, just aiming and moving the backhand in or out. One thing about this method that is never or hardly ever mentioned that drives me nuts is this; Sometimes when players do this they actually change their aim off to the side of the intended english and then squirt helps them make the ball and that's why some people can't use the predator and make the ball. I know it might be hard to understand but when I pivot over I am changing the aim or angle of the stick BUT I am not changing the aim line and that's why I can aim center to center then pivot and stop the ball spinning with the Z shaft.

#2 front hand pivot, just aim it up, keep your back hand still and adjust your bridge to the desired tip position. You have to be careful not to slide your backhand over in the same direction cuz now you're coming close to adding a bit of parallel and that'll cause you more squirt.

#3 A little of both, which I like to do when I'm playing. You use a little movement in the bridgehand (to the right for right spin and left for left, obviously) and then a little in the backhand in the opposite direction (backhand goes left for right spin and vice versa)

Most current pros do not usually aim center and then pivot but they do fall on the shots with their sticks angled off and if you were to ask them to stop after they set up to the shot you would probably be able to move the butt of their cue in or out and their tip would be very close to center ball and set on the aim line. They can do this because of years of learning that angle that they fall on the shot with. You can speed up your learning process by first aiming center and then pivoting over to that angle and once that has been accomplished you may choose to simply fall on the shots with your stick angled off also. I've played both ways and can tell you when under extreme pressure I prefer to fall on the aim line with center (because that requires less feel or guess work) and then pivot to apply my english. BUT when playing and in stroke you may find me simply walking into the shots with the side spin already applied, skipping the center ball step.

I recommend no matter what cue you use that you become and expert at setting up straight in shots and start applying all the different tip positions you'll be using in the game. If you can't do it on straight in shots you're leaving a lot to luck on all your other shots. Use at least the 3 methods I suggested and see which one feels the best to you and which one you think you can master. It's an area that needs to be mastered if you have plans of playing at a decent level. You need spin and you need to be confident and consistent when using it.

The question I have about all of this is what is the best way to apply spin using a standard non-low deflection shaft, and using a low deflection shaft? Is method 1 best for standard deflection and method 3 best for low deflection? Currently I have a standard shaft that I haven't yet measured for deflection. At some point I would like to get a low deflection shaft. I don't want to get used to applying spin using method 1, then have to re-learn to spin the ball using 3 when I go with a different shaft.

 

[Jaden]

Jal, great diagram. I've always wanted to draw that same diagram myself and post it, but just never got the time. But since you did already, I want to bring up a nagging question that has always bothered me whenever I read physics papers on squirt. Maybe you can help me out.

Looking at your diagram, you can break up the net force of the cue in its tangential component and its normal component. Essentially, the net force is the summation of these two forces, correct?

If you just examine the tangential force component without the normal component, then the CB would spin as the result of this force. However, the CB wouldn't go anywhere because there is no normal force to move its center of mass. Essentially, the CB would just spin like a top.

If you just examine the normal force component without the tangential component, then the CB would accelerate in the direction pointed by the normal vector. However, the CB would have no spin because there is no tangential force.

Again, the net force is the summation of the tangential force and the normal force. So if you want to find out the resulting spin and direction of the CB experienced by the net force, can you not just superpose the above results? Wouldn't that mean the CB would have some spin and that it would depart in the normal direction?

The direction of the CB is what I want to focus on, because that's not what you would expect, nor that is what you see in real life. What you see is that the CB departs in the direction very close to vertical. But if you break down the problem in the way that I described above, this is the result that you get. So my question is...what is wrong with my analysis? Can I not break up the net force to its tangential and normal components and combine the results?

The problem that you are describing is what I was trying to get at. In the real world you have all sorts of variables. the compression and malleability of the tip the flexibility or rigidity of the shaft. The mass of both the cue(this can vary with grip type and speed) and the CB(can vary depending on the type of CB). Also the amount of chalk and roughness of the tip affects this as well.

As the tip is contacting the ball you first have direct force applied to the tip straight back and as the tip and ball interact, the tip compresses. In the diagram, the majority of mass of the CB is at a right tangential plane in relation to the mass of the shaft and cue, but they don't interact on a strict mass to mass ratio becuase you have the compression of the tip and the compression of the shaft at an angle opposite the tangential plane of the interacting masses. The tip does not slip off of the ball and instead pushes through, but because of the offset compression of the tip and the offset bow of the shaft due to the tangential interacting masses, the cue is not pointing in the original direction when the ball leaves the tip. It is this interaction of the masses in conjunction with the other interplaying forces that cause the ball to travel not in line with cue or tangential to the line of the cue but at somewhere in between depending on the rigidity of the shaft (at various points as well, which is why taper plays such a significant role in playability), the roughness of the tip and balls(dirtyness usually), and type and roughness of the felt (to a lesser degree) and how hard it is hit. The harder it is hit the more bow of the shaft and the shorter the angle.


Because of all of the interplaying variables. it is difficult to use standard formulas of physics to have any real results and most of the variables play an extremely small role in the interplay and are often not even necesary to adjust for.

 

[inthezone]

Jim,
It is good to clarify that there is this constant pivot point, though I would like to know how much this pivot point varies with speed and offset. I'm sure it must vary somewhat, but we'll need some accurate testing methods to ascertain the variation.

Regarding the higher 30-50" pivot point estimates, I just cannot believe we are measuring the same things. My hundreds of hours of testing closely correlate to Platinum's test results.

I'm not sure what has caused of this difference of opinion regarding a correct measure of pivot points.

Colin

Yes, the Platinum Billiards numbers are correct.

There is no mystery - the "shoot into an object ball until the PP is found where the CB spins in place test" is greatly flawed due to the throw effect.

Try this test on a break shot (50") and you will find that the true PP is only lengthened by a couple inches over PB's numbers due to the throw effect. Try the same test with the OB just 10" away and the throw effect will falsely lengthen the apparent PP by more like 2 feet. This is why it is pretty much useless in actual play.

I have metioned before another method which is simple to set up and should convince anyone that tries it:

1) set up a couple of pins slightly more than a ball apart to create a "gate"

2) put a piece of masking tape on your shaft and mark in inches from the tip.

3) Align center ball to shoot thru the gate

4) hold the bridge hand still and pivot so that as example, the tip moves to apply right english and stroke.

5) if the CB hits the left pin, shorten the PP, if it hits the right pin, lengthen it.

This so simple to set up - use two bic lighters...whatever...anything to make a "gate".

 

[NaturalEnglish]

I got a reply from Joe T. He said the shaft he is using in the laser trainer video is a Predator Z shaft. When I use those shafts on straight in shots with BHE I ob seemed to be thrown more than a conventional shaft. Maybe its just my inconsistent aiming? Is this thread on BHE getting clearer or more confusing?

 

[Joe T]

I don't think they're throwing more, I think when you're changing your tip position say over to the right you are also changing your aim line slightly over to the right and because these cues don't deflect back in much you are actually just hitting the object ball more to the right so it looks like it's throwing it over more. But that's just a long distance guess.

 

[Joe T]

geek I really can't tell you which is best for you. I can just ask you to go to the table and try'em all and see which one you like best. I think once you learn to do it one way you be able to learn the others faster and the switch that may come later won't be so tough.

 

[Jal]

...Looking at your diagram, you can break up the net force of the cue in its tangential component and its normal component. Essentially, the net force is the summation of these two forces, correct?

If you just examine the tangential force component without the normal component, then the CB would spin as the result of this force. However, the CB wouldn't go anywhere because there is no normal force to move its center of mass. Essentially, the CB would just spin like a top.

If you just examine the normal force component without the tangential component, then the CB would accelerate in the direction pointed by the normal vector. However, the CB would have no spin because there is no tangential force.

Again, the net force is the summation of the tangential force and the normal force. So if you want to find out the resulting spin and direction of the CB experienced by the net force, can you not just superpose the above results? Wouldn't that mean the CB would have some spin and that it would depart in the normal direction?

The direction of the CB is what I want to focus on, because that's not what you would expect, nor that is what you see in real life. What you see is that the CB departs in the direction very close to vertical. But if you break down the problem in the way that I described above, this is the result that you get. So my question is...what is wrong with my analysis? Can I not break up the net force to its tangential and normal components and combine the results?

Thank you very much Jsp. Always good to hear from you.

I have a degree in this stuff from way back when, but your very question plagued me when I got back to it. It's like having a degree in math, but forgetting a digit between one and ten. (However, there is a story about some Nobel Laureates visiting the University of Chicago, and agreeing to take elementary level tests in their respective subjects. They did horribly, as the story goes. Some, I think, even failing. This was told by a professor at the university, Milton Rosenburg, on one of his nightly radio programs, so it's likely true. Maybe I shouldn't feel too bad.)

Anywhoo, the answer is that a purely tangential force (a component in our case) will not only cause spin, but will propel the object in the direction of the force, as if it were operating through the center of mass. F=ma applies just as much here as with a head on collision. But we have to be careful (and this is what bugged me and maybe you too), because it seems as if this might violate the conservation laws. After all, it looks as if just moving the point of application from center to edge gets you additional spin energy (along with the same translational energy you would get from a head on collision.)

The answer to that is to consider the size of the force when a body collides with our object. It will be less if the contact is toward the edge than if it's directed through the center of mass. As a result, it won't acquire as much translational velocity as a necessary payment for the spin it gains. And the colliding body will of course be affected differently, so the conservation laws will be okay with the whole thing.

Of course, the tangential force is only one component at the tip/ball. The net force, which is the sum of it and the normal component, gives the cueball its final direction. And, just to mention it, the force is not constant but builds up and then dies away during impact. The diagram really represents an average force, both in magnitude and direction. (I know you know.)

Hope that answers it, but if you see any problems, fire away. (There are several questions I have about the nature of the force as it evolves, and they aren't too easy to answer.)

Jim

 

[JimS]

Again my thanks. If I can do something for you, let me know.

It's tough to tell where the pivot point is located on your cue. It would help greatly if instead of using a fixed pivot loacation of 12", that you vary it until the object ball takes off as perfectly straight as possibles (ie, along the line joining the center of the cueball and object ball before the shot is made). This can be very awkward if the cue's intrinsic pivot point is far from the tip, but trying to calculate from the object ball's direction is very inaccurate. It would be interesting to know if it was, say, at least greater than 20-30" from the tip, as your earlier trials seem to indicate.

Also, from your results, it looks that swerve is affecting them somewhat. The balls need to be only about a diamond apart with a hard hit to get rid of this.

Again, I don't expect anything, but would be interested in the results of any further testing you do. Please thank your wife too.

Jim

I think I learned from the testing of various positons where the pivot point is... or at least I thought I had.

I had moved the pivot point forward and back on my playing cue until I got the ob to go as straight as possible and then after I discovered I was throwing the ob somewhat, even when shooting fairly hard, I re-tested my cue. The 12" figure I quoted is the pivot point that appears to be accurate but then I have to allow for throw and/or swerve but I'm getting minimal squirt.

 

[Jal]

I think I learned from the testing of various positons where the pivot point is... or at least I thought I had.

I had moved the pivot point forward and back on my playing cue until I got the ob to go as straight as possible and then after I discovered I was throwing the ob somewhat, even when shooting fairly hard, I re-tested my cue. The 12" figure I quoted is the pivot point that appears to be accurate but then I have to allow for throw and/or swerve but I'm getting minimal squirt.

Let me see if I have this right. You retested your cue and found that the object ball was going straightest when pivoting at about 12" ? If so, was the object ball wetted and how far was the cueball from the object ball? (If you minimized throw and swerve, then the answer is at hand, but it's not yet clear to me if you did.)

Jim #2