modifying the tangent line

[ShootingArts]

using this from RandyG

What is the definition of "contact and release points?"

If the balls did "gear" for large amounts of spin on the cue ball, you would see skid/cling far more often. From this I think it is fair to conclude that "gearing" -- that is, the relative tangential motions of the two surfaces going to zero -- is fairly rare for significant amounts of spin on the cue ball.

Bob,

I'm "borrowing" release point from RandyG. It explains a little more clearly the point where significant contact ends I believe. I really like it to define tip contact with the cue ball and will use it in the future. Contact point is a vague term at best since it isn't a point to begin with when we start really discussing these things. To be a little more specific I should be talking about initial contact point and release point but we can bog down in details.

Please bear in mind that we are largely splitting hairs with this entire conversation but the very fact that skid and cling to a level to disrupt a shot are possible at all is a very strong indication that lesser degrees of the same phenomenon are very possible and normally pass without notice. You can hardly say that the phenomena is possible at ten times or fifty times the magnitude but not to the lesser degree.

Hu

 

[TX Poolnut]

My head hurts.

 

[LAMas]

If it is perpendicular to the line to the pocket, why don't I scratch into the other pocket on a spot shot to the corner pocket?

 

[randyg]

Hit a pure stop shot and you will.....SPF=randyg

 

[Spike8ball]

Hit a pure stop shot and you will.....SPF=randyg

Thanks to you Randy, I actually get this...

Mike

 

[pool101]

Here is a video that helps go to 1:40 to get past the ad.
http://www.youtube.com/watch?v=CVSIFWbrB80&feature=player_embedded

 

[CreeDo]

Lotta nits to pick here... No idea what the point of the thread is, except maybe to draw a distinction between the mathematical concept of the tangent line (which is infinite and abstract) vs. the real world concept of the cue ball's path and whether it truly goes along that line. The former doesn't change, the latter does.

Not sure about hu's point of using jacked up sidespin to change the path. Or maybe the change in path there has nothing to do with the sidespin let's say. If you use a masse shot on the CB to immediately an OB, the CB bends back off the tangent line. But as with other sidespin shots, the amount it bends off the line is directly related to the amount of follow or draw. The sidespin is irrelevant even if the ball is spinning on a funky diagonal axis vs. a traditional draw shot that's spinning on a perfectly vertical axis.

 

[Island Drive]

Lotta nits to pick here... No idea what the point of the thread is, except maybe to draw a distinction between the mathematical concept of the tangent line (which is infinite and abstract) vs. the real world concept of the cue ball's path and whether it truly goes along that line. The former doesn't change, the latter does.

Not sure about hu's point of using jacked up sidespin to change the path. Or maybe the change in path there has nothing to do with the sidespin let's say. If you use a masse shot on the CB to immediately an OB, the CB bends back off the tangent line. But as with other sidespin shots, the amount it bends off the line is directly related to the amount of follow or draw. The sidespin is irrelevant even if the ball is spinning on a funky diagonal axis vs. a traditional draw shot that's spinning on a perfectly vertical axis.

I heard it yrs ago, in So. Illinois at Jansco's, from Ronnie Allen ...."whitey 'never' lies"!

 

[Calgaryplayer]

How can the tangent line be modified?

I think the eastest way to explain to you is looking at the following equation:

+ amxnym−1]wx − [g(x) + anxn−1ym]wy = 0
[eαxf + cβ]wx − [eβyg(x) + cα]wy = 0.




I hope it helps!!!

 

[LAMas]

Hit a pure stop shot and you will.....SPF=randyg

Thanks it helps with caroms....1/2 tip below center.

 

[KMRUNOUT]

Linda...I'm surprised at your comment. English (sidespin) has NO influence on tangent line, WITHOUT draw or follow...until the CB strikes a rail. Speed has no affect on tangent line either...unless there is draw or follow. A high speed stun shot merely travels down the tangent line until the CB strikes a rail...and then the CB comes off the rail at the same angle it went in at.

Scott Lee
www.poolknowledge.com

Scott,

That depends on whether you believe in english induced throw. If you believe that you can "throw" the object ball off line with english, then the argument could be made that you could make the ball with a fuller hit (or thinner), and get it in the hole with english. The fuller (or thinner) hit would result in a different tangent line. In my experience, I sometimes have a relatively mild cut shot (like say 10 degrees). I frequently will use outside english to achieve some "throw", so that I can effectively hit the object ball almost dead full, spin it into the hole, and draw the ball much straighter back than without using english.

While the english *itself* does not change the tangent line, it allows for a different contact point, which by definition *does* change the tangent line. This of course all depends on your belief in spin induced object ball throw (and not everyone believes in this for some reason.)

KMRUNOUT

 

[KMRUNOUT]

The tangent line is the tangent line is the tangent line. It cannot be modified. You may modify your aiming point along the tangent line for
various reasons but the tangent line is an absolute.
My definition of a tangent line is; A plane shared by the CB and OB when , all other things being equal, it is perpendicular to a line drawn through the center of the CB, OB, and center of the target pocket
Flame time

your definition is totally fine. except that you can eliminate the last part about the target pocket. The tangent line is (by definition) a line adjacent to a circle which is perpendicular to the radius of the circle at that point. You really only need 1 ball to describe a tangent line, but the cueball makes for an easier visualization of *where* on the object balls radius your tangent line is touching (the contact point).

KMRUNOUT

 

[KMRUNOUT]

This is an extremely important concept to grasp for understanding how to move the CB. There is absolutely no influence on the tangent line by side spin directly.

Now I say directly because some folks get confused and misunderstand a subtle difference that occurs with applying sidespin. I've had to explained that to folks I've taught in the past. I'll make my feeble attempt to explain exactly what I mean and where I've seen the confusion come.

There are two objectives that get slightly confusing. 1. contacting the OB at the same specific and exact spot and 2. The ability of sidespin to influence the path of the OB.

Forgetting about pocketing an OB for a moment and talking simply about contacting an OB with the CB at the specific point "A". Given this exact same contact point on the OB you can apply any amount of left or right hand spin and the CB will come off the OB at the same angle regardless of the sidespin.

Now, where I've seen some folks get confused while attempting to pocket an OB. Folks will insist that in an effort to miss hitting another OB or in an effort to avoid a scratch they will apply english (sidespin we are talking here .. NOT TALKING FOLLOW OR DRAW) and they insist this side spin changes the path of the CB and avoids the unwanted kiss or scratch.

Well, yeah it does, but that's not cause the tangent line's diversion has been changed. It's because the side spin allows you to throw the OB, which in return allows you to CHANGE the spot on the OB you are contacting. When you hit the OB in a different place you get a different deflection ( a different tangent angle based on hitting the OB in a different place.)

well said. I agree.

KMRUNOUT

 

[KMRUNOUT]

Huh? The tangent line is of infinite length.

If you were expressing the tangent line in terms of a vector, then no, it isn't infinite length. The length would vary depending on the velocity of the cueball in that direction. However, in the conventional sense of a "line", you are 100% correct that it would have infinite length. I wonder if the poster you quoted was thinking in terms of vectors...

KMRUNOUT

 

[KMRUNOUT]

True tangent line is cause/effect without follow or draw during contact of cue ball with object ball also, on a cut shot as you increase the speed of your cue ball the tangent line will change more/quicker the fuller you hit the ball you are cutting.

No, the tangent line will not change with respect to the variables you noted. The tangent line is a constant value given a particular contact point.

KMRUNOUT

 

[KMRUNOUT]

Technically, the tangent line itself can be modified, but only by introducing the 3rd dimension (altitude). Assuming the line from the OB to the pocket can't be changed, there are actually many contact points on the OB that the CB can hit to send it there, and each contact point will define its own tangent line. Of these contact points, however, only one can be struck if we presuppose that the CB is on the bed of the table. Assume an airborne CB, though, and quite a variety of tangent lines can be achieved.

I admit, however, that this post is not constructive. The tangent lines that aren't coplanar with the bed of the table are effectively impossible to utilize with any acceptable measure of accuracy and control.

-Andrew

Although Andrew, your point is certainly valuable and might flash through someone's mind the next time they walk over to pick up the cueball off the floor after launching it there on the break lol!!

KMRUNOUT

 

[KMRUNOUT]

Maybeto create a I'm misunderstanding the question.

IMO the tangent line is defined by the line perpenticular to the line formed by the contact point of the two balls. That can't be changed. Only the contact point can be changed to create a different TL. Applying follow or draw will not change the line either. It will only change the path after the tangent is taken which must happen for ?some distance. Only speed differences can change the amount of distance the CB follows the TL before the follow or draw changes the CB path.

you are 100% correct

KMRUNOUT

 

[KMRUNOUT]

What a great post.

First off, I agree with Scott Lee that "pure side spin" will have little or no effect on the Tangent Line.

Second. Remember that the Tangent Line is from the release point not the contact point....SPF=randyg

Randy,

Your second point is unclear. Could you explain the difference between "release point" and "contact point"?

Also, is the pool use of the term "tangent line" somehow different than the mathematical term? In math, all that is required is a point on the surface of a circle or sphere, and the location of the center of that circle or sphere. Those two points define a line. A line that is contacting the surface of the circle or sphere at the previously mentioned spot, but is perpendicular to the line formed by that point and the center, is said to be "tangent" to the circle or sphere at that point.

Thanks for any further explanation you can provide,

KMRUNOUT

 

[KMRUNOUT]

You don't really believe this, do you? The balls don't stick together and then come apart, the collision is practically instantaneous. The tangent line is a different line when the balls are not of the same mass.

To explain in detail: The vector component of the CB's momentum in the direction the OB ends up going is key. If the balls have the same mass, this component is transferred entirely from CB to OB, meaning it ends up being 0 in the CB after contact. A 0 magnitude in the vector component in that direction means 100% of the momentum remaining is perpendicular to that direction, hence the 90-degree rule. With a heavier CB, the amount of that component transferred to the OB is not 100%, it's a little less. You can see this by hitting a sliding-ball dead-straight shot. With balls of the same mass, the CB stops dead. If the CB is heavier, the CB will follow a little, even when sliding at contact. This is the momentum in the OB's final direction that the CB retains after contact, and it's the same momentum that contributes to the change in tangent angle. Non-zero component in this direction means the resolved vector direction is no longer perpendicular to the OB direction.

-Andrew

Well said. 100% right.

KMRUNOUT

 

[KMRUNOUT]

If it is perpendicular to the line to the pocket, why don't I scratch into the other pocket on a spot shot to the corner pocket?

You do with a sliding cue ball. Every time.

KMRUNOUT