prove me wrong

[td873]

my small brain doesn't comprehend tangent lines on perfectly straight
shots.
(1) The only physically possible reaction is a follow or draw.
(2) please tell me why the OB isn't spinning at a similar rate
to the CB. I'm dying to know.

First, you are now discussing spin transfer, and not OB trajectory (as in your original post). Another moving target. But to address your questions:
(1) Wrong. [Newton (3)]. As a simple sanity check, why couldn't the ball go UP? that's not follow or draw. Similarly, spin will cause some other effect.

(2) (a) Because they are spheres, (b) because the contact point is very small in proprotion to the ball size, (c) because the balls are only 2.25" in diameter, (d) because this isn't a perfect collision, (e) because the collision is for a fraction of a second, (f) because of the polished surface.
Thus only a perctage of spin is transferred. This is a calculatable amount based on physical properties. Pull out your copy of the "Science of Pocket Billiards" to confirm via experimental data.

As a simply sanity check: if the balls were "sticky" (perhaps with glue on them) - the effect would be obvious. Lessen the "stickiness" you get less transfer.

In fact, it's clear you understand this by your caveat of "clean" object balls. That is, your statement concedes that you understand the effect of friction on spherical collisions.

-td

 

[td873]

Someone here can surely convince me that I'm wrong.

One last piece of this puzzle.

Jack Kohler published a very thorough description regarding this back in the late 80's. Using mechanical devices for repeatability (i.e., no human error), he calculated various throw angles based on english enduced throw for all cut angels from 0 to 90°. If you review his efforts, and have any comments, please post them. At that point we should be on the same page to have an informed discussion.

Lastly, here is a shot that Jack uses to illustrate the existence of EIT throw.

CueTable Help

Set the shot up so that the 1 cannot be made with a center ball hit. As shown. When applying outside english, the 1 goes in. Thus, there is english enduced throw.

Please set this up yourself - using hole punch reinforcement circles to mark the balls. After you confirm this for yourself, please let me know if this needs additional discussion.

Otherwise, due to scientific proof, mathematcial confirmation, experimental data, and your own experience based on the shot above, I believe this thread is closed.

-td

 

[John Barton]

this is contact induced throw, not spin induced throw.
IMO, you can't use CIT on a dead straight shot, only on a cut shot.


SIT implies that spin transferred from the CB to OB
will change the intended trajectory of the OB.

thanks for all the replies, relevant or not.
I'm still wondering why Dr. Dave is the only
one to video document these principles.


I've still seen no evidence of SIT.

Um, when there is no possibility of anything but a dead-on hit then any throw of the object ball can ONLY be caused by spin/friction. That was the whole point of DD's video.

Perhaps DD is the only one doing these videos because he made the physics of pool his doctoral thesis. If true then that would be a pretty good motivation. But he is not the only one who videos what happens when balls collide and are hit with sticks. The Jacksonville Project also has some interesting video as does another European project.

I have seen two things discussed here - throw and spin transfer. Both things exist and are provable. And they have been proven. So, like Bob Jewett is fond of saying, the burden of proof lies with those who claim it doesn't exist. It is up to you to show why the video proof is different than what is claimed.

As for the example you gave with the object ball being four balls out. It may indeed be possible to throw the object ball into the pocket. The example you gave simply depends on contacting the object ball with enough spin. Other than being one more ball out and adding a ball to insure you contact the object ball full the setup is the same as DD. Except if you take away the control ball nearest the cushion as in Dr. Dave's shot then it would be possible to contact the object ball on that side due to human error.

But IF that happens - that the cueball contacts the object ball on the cushion side - which is the wrong side to pocket the ball - AND it still goes in then that is even MORE evidence of spin induced throw. So the example, as designed makes it impossible to hit the side of the object ball to cut it normally, only possible to hit it full or on the wrong side.

So please explain how it's physically possible for the object ball to throw so much in the direction of the pocket when it's impossible to hit it with anything close to pocketing angle.

 

[Ballistic Billiards]

It might help if you chuck the ideas of CIT and SIT aside.

I think this is the best idea, however, "throw" seems to carry too many
definitions.

This thread has gone in a lot of directions, my initial interest was in
the effect of spin in a collision and the practical applications.

I think if you want to "throw" the ball, you don't need maximum
side spin.

here's my take on it
shot 1 is not possible
shot 2 you could throw

CueTable Help

notice I said you could.
how do you do it?

If this isn't a good example of how to use throw in a practical
situation, what is?

 

[John Barton]

JAL,

When the object ball is thrown I don't think that the object ball is curving or masse'ing. I think it is getting pushed to the side before it begins the forward journey.

any thoughts on this idea?

To me a masse is a result of spin and friction forcing the ball to go away from it's initial path. I don't think that enough spin can be imparted to the object ball to make this happen even slightly.

 

[John Barton]

I think this is the best idea, however, "throw" seems to carry too many
definitions.

This thread has gone in a lot of directions, my initial interest was in
the effect of spin in a collision and the practical applications.

I think if you want to "throw" the ball, you don't need maximum
side spin.

here's my take on it
shot 1 is not possible
shot 2 you could throw

CueTable Help

notice I said you could.
how do you do it?

If this isn't a good example of how to use throw in a practical
situation, what is?

Actually the way you have it diagrammed it's probably nearly impossible to make the object ball using the throw technique. However depending on how soft the pockets are it could be possible to throw the object ball and give a little spin to help it into the pocket.

No,maximum sidespin is not required to throw the object ball. But the amount of speed and spin depends on several factors that come with experience.

I am sure it could charted but this is something that players of higher caliber just know how to do.

I don't think throw has many definitions. But I do think that the attempts to label and classify all the effects that happen in billiards is classic rational vs. romance philosophy. We know the effect exists, now how to describe it and break it down into it's parts.

A good book to read would be Zen and the Art of Motorcycle Maintenance.

 

[Jal]

...I think if you want to "throw" the ball, you don't need maximum side spin.

Agreed 100%. About 1/2 maximum sidespin yields the most throw according to theory. But this will vary somewhat with ball conditions.

here's my take on it
shot 1 is not possible
shot 2 you could throw

CueTable Help

notice I said you could.
how do you do it?

It's not clear what you're trying to do in the diagrams other than to maybe put some helper english on the OB, as John Barton just described. Td873's diagram above is the typical situation where throwing the object ball via english on the cueball is necessary.

Jim

 

[td873]

This thread has gone in a lot of directions, my initial interest was in the effect of spin in a collision and the practical applications.

Sounds like you are backtracking a bit. Your original post was titled

prove me wrong

And you stated:

I'm of the belief that you can't transfer enough spin, on a clean set of balls, to make a significant change to the trajectory of the OB.

I reread it, but didn't see anything about practical application. Rather I noted the explicit challenge to show that it EIT exits. After 50+ posts, it seems you are now changing your position to question how you can apply spin to help your game (i.e., practical application). Unless I misinterpreted your various responses, I believe you have just conceded your original point.

That is, it has been proven to you to the extent that it now has "practical applications."

-td <-- is this thread done yet?

 

[Jal]

JAL,

When the object ball is thrown I don't think that the object ball is curving or masse'ing. I think it is getting pushed to the side before it begins the forward journey.

any thoughts on this idea?

To me a masse is a result of spin and friction forcing the ball to go away from it's initial path. I don't think that enough spin can be imparted to the object ball to make this happen even slightly.

John,

I'll go along with what you said 99% (maybe 99.9%) of the way. There are a couple of things which do, in theory, cause the OB to masse after CB/OB impact (besides an airborne cueball). But they are very small effects, according to calculations, and would require a very precise test setup to even detect them. Since they are so small, I'll resist the temptation to describe them unless you or someone is interested.

There are many times though when it does appear to me that the object ball visibly curves. Whether this is an optical illusion or not, I don't know. If it is in fact curving, it's almost certainly due to a flying cueball as I think the calculations for the above mentioned phenomena are likely right.

So your statement "I think it is getting pushed to the side before it begins the forward journey." is for all intents and purposes, correct, imo.

Jim

 

[Ballistic Billiards]

didn't mean to be vague

Sounds like you are backtracking a bit. Your original post was titled

And you stated:

I reread it, but didn't see anything about practical application. Rather I noted the explicit challenge to show that it EIT exits. After 50+ posts, it seems you are now changing your position to question how you can apply spin to help your game (i.e., practical application). Unless I misinterpreted your various responses, I believe you have just conceded your original point.

That is, it has been proven to you to the extent that it now has "practical applications."

-td <-- is this thread done yet?

The part about spin changing the trajectory significantly(practical).

If you're pushing the ball off line and recalculating a new path
that's one thing.

This is a significant concern, however, the addition of side spin
only seems to cloud the issue and do little for the OB, as usual.

Did it take 50 posts because I was unclear?

In any case, I have some ideas on how to test these
effects if anyone has anything to contribute, let me know.

 

[Ballistic Billiards]

zero degrees

let's talk theories...

explain the cause and effect of hitting a zero degree cut shot (straight)
with spin.

I'll start..

ball A contacts ball B with 0* of cut angle @ 1 mph with stun.
ball A stops due to the stun
ball B leaves the collision exactly opposite ball A, 180* @ 1mph.


if ball A is spinning @ 10rps (clockwise, left side) then
ball B leaves with 10rps(counter-clockwise)

equal and opposite right?



cOOp<---dumb construction worker
--these numbers are just for the sake of simplicity.

 

[fred_in_hoboken]

let's talk theories...

explain the cause and effect of hitting a zero degree cut shot (straight)
with spin.

I'll start..

ball A contacts ball B with 0* of cut angle @ 1 mph with stun.
ball A stops due to the stun
ball B leaves the collision exactly opposite ball A, 180* @ 1mph.


if ball A is spinning @ 10rps (clockwise, left side) then
ball B leaves with 10rps(counter-clockwise)

equal and opposite right?



cOOp<---dumb construction worker
--these numbers are just for the sake of simplicity.

Not exactly.

"Equal and opposite" refers to the forces involved. The frictional force acts on both balls equally, but this force is not necessarily enough to stop the rotation of the cue ball. The amount of the frictional force will be proportional to the coefficient of friction. The higher this coefficient (eg, the dirtier and stickier the balls), the higher this force will be, and thus a higher proportion of the spin will be transferred to the object ball.

However, because the object ball is not fixed to its axis, a portion of the frictional force will result in kinetic motion along the tangent line- (eg, 90 degrees from the direction of motion of the cueball). The amount of energy converted to motion on this direction will be proportional to the mass distribution of the object ball and its radius. Whether this force will result in a significant deviation from the line of motion predicted by the contact points is hard to calculate, but experience (and Dr Dave's videos) suggest that it does. (significant means a few degrees, which can be the difference between make and miss).

 

[JimS]

At some point it's necessary to understand that throw does occur and then go to the table and work on using or avoiding or providing for the throw.

 

[mikepage]

[...]
ball A contacts ball B with 0* of cut angle @ 1 mph with stun.
ball A stops due to the stun
ball B leaves the collision exactly opposite ball A, 180* @ 1mph.


if ball A is spinning @ 10rps (clockwise, left side) then
ball B leaves with 10rps(counter-clockwise)

equal and opposite right?
[...]

No.

This is the reason all you instructors out there should cease and desist from ever mentioning interlocking gears as an explanation here. Yes, it's easy to understand. But it leads to wrong conclusions like this one and wrong predictions like that more cue-ball spin will generate more throw.

The surfaces of the two balls are never stuck together; they never move at the same rate; the cue ball never grabs the object ball.

Instead the fast-moving cueball surface swipes across or rubs across the object ball, like a broom rubbing across a floor.

So for your straight-on shot,

if ball A is spinning @ 10rps (clockwise, left side) then
ball B leaves with 0.2rps (counter-clockwise)

 

[mikepage]

duplicate post deleted

 

[MrLucky]

You are....

People are always talking about throwing balls with spin (SIT - spin induced throw)

I can throw it more this way or I had to throw it in, etc.

I'm of the belief that you can't transfer enough spin, on a clean
set of balls, to make a significant change to the trajectory of the OB.

Someone here can surely convince me that I'm wrong.

SO WRONG!!!! it does require a good stroke !

 

[randyg]

You're not a nit for challenging a theory. Some of the stuff propagated by pool instructors, pros and "physics" people does turn out to be wrong. But you seem to be fixed on the idea that the spin put on the OB (if any) is the cause of the throw. Several posters have pointed out that this is not the case, but you persist. Until you rid yourself of this notion, you'll continue to struggle with the concept.

Spin induced throw (SIT) means throw resulting from spin on the cueball, not the object ball. If the OB is thrown, it will inevitably acquire spin while being thrown (during impact). But this spin will only cause it to masse very slightly according to my understanding. As everyone has been saying, it's the friction between the balls while they are in contact that does the deed.

It might help if you chuck the ideas of CIT and SIT aside. Think in terms of relative surface velocity between the points of contact of the two balls. This can be due to cut angle and/or spin on the cueball. During impact, friction acts to reduce this surface velocity (to zero in many cases). In other words, it undergoes a change.

The object ball always acquires 1/7'th of this change in surface speed as linear velocity, and 5/14'ths of it as spin (the product of its radius R X its spin rate W is equal to 5/14'ths of the change in surface speed). Its acquired linear speed is in the direction of the initial surface velocity between the contact points, which may be up/down, sideways, or anything in between. Only the sideways component is important as far as shotmaking is concerned.

But the point is that all this happens during impact, and that the spin it picks up is not a cause of throw. You might call it a side effect.

Jim

Well stated JIm, thanks...randyg

 

[Omar]

this is contact induced throw, not spin induced throw.
IMO, you can't use CIT on a dead straight shot, only on a cut shot.


SIT implies that spin transferred from the CB to OB
will change the intended trajectory of the OB.

thanks for all the replies, relevant or not.
I'm still wondering why Dr. Dave is the only
one to video document these principles.


I've still seen no evidence of SIT.

I have a couple of issues with your analysis. If Dave is cutting the ball the left as you claim, the contact induced throw would throw the ball to the right away from the pocket, not toward it. Secondly, even if he did not execute a perfectly straight hit, the interfering ball still precluded the possibility of contacting the object ball at the point opposite the pocket, which the ghost ball system would suggest as correct. And we all know that you have to cut the shot slightly thinner than that due to contact induced throw.

 

[Ballistic Billiards]

is it that tricky, really?

I have a couple of issues with your analysis. If Dave is cutting the ball the left as you claim, the contact induced throw would throw the ball to the right away from the pocket, not toward it. Secondly, even if he did not execute a perfectly straight hit, the interfering ball still precluded the possibility of contacting the object ball at the point opposite the pocket, which the ghost ball system would suggest as correct. And we all know that you have to cut the shot slightly thinner than that due to contact induced throw.

If the OB "should" hit the short rail, three balls from the side rail with a
full hit (no cut). Tell me how he manages to hit the ball full (no cut)
and hit the long rail, one diamond up from the pocket. This "interfering"
ball can't.... oh nevermind.
Go watch the video and tell me it's not edited and the balls have
changed position.

0* seems to be a scary place to be if you need to throw the ball.
no one has any comments on how a 0* hit results in anything but
a 180* trajectory...

I kinda like the fact that people out there think they can break
the laws of physics on the pool table.

-cOOp<--tired of this thread
who wants to play some?

 

[Ballistic Billiards]

i was not clear again

No.

This is the reason all you instructors out there should cease and desist from ever mentioning interlocking gears as an explanation here. Yes, it's easy to understand. But it leads to wrong conclusions like this one and wrong predictions like that more cue-ball spin will generate more throw.

The surfaces of the two balls are never stuck together; they never move at the same rate; the cue ball never grabs the object ball.

Instead the fast-moving cueball surface swipes across or rubs across the object ball, like a broom rubbing across a floor.

So for your straight-on shot,

if ball A is spinning @ 10rps (clockwise, left side) then
ball B leaves with 0.2rps (counter-clockwise)

and so what of the trajectory?
which is the original topic of this discussion.