NV B.7 - Pool Ball "Turn" Caused by Spin

[DrDaveBilliards]

@jtube1997

I'm not a science teacher (I'm an engineering professor), but I am a dumb-ass at times. Regardless, I love pool more than most people who play.

[700kotchi]

Dear Dr. Dave --I've been playing since I was 14 yrs. old--44 yrs. and I'm as good as they come so I guess when I say you don't know what you're talking about --I speak from experience. Why don't you switch sides so the tape doesn't keep the ball straight.

[DrDaveBilliards]

@700kotchi

The cue ball does swerve after being struck (with English and a non-level cue), but only while it is sliding. Once the cue ball starts rolling (with or without sidespin), it heads in a straight line. The measuring tape has nothing to do with it.

See the "swerve" section of the FAQ section of my website (the link is in the video description) for more info, demonstrations, and explanations.

Thank you for the comment (even if you don't like the video),

Dr. Dave

[stardustie]

im a bit confused, im used to adjust my aiming point when i'm using spin but this vid says i shoudnt? when i watched this vid i noticed ur cue wasnt straight with the table..?

[DrDaveBilliards]

@stardustie

When using English, you must adjust form squirt, swerve, and throw. For more info, see "aiming - aim compensation" in the FAQ section of my website.

The purpose of this video was to show that a ball rolling with sidespin (after squirt and swerve have occurred) travels in a straight line.

[GetMeThere1]

OK, so as I've spelled it out elsewhere, I see it now: balls can actually roll in a completely legitimate "rolling action," in a STRAIGHT LINE, on axes of rotation other than horizontal--as long as the axis is perpendicular to the direction of rolling :)

Axes other than those perpendicular to the initial direction are masse shots.

[DrDaveBilliards]

@GetMeThere1

Good job, and good description.

Whenever the axis of rotation is in the vertical plane, the ball is rolling. If the axis is not in the vertical plane, the CB is sliding (e.g., during the swerve portion of any shot with English, not just masse shots).

Thank you for the interesting discussion. I'm glad we've finally reached common ground.

[DrDaveBilliards]

@DrDaveBilliards

Actually, the ball can also be sliding when the spin axis is in the vertical plane. See the spin-axis-flip demo (NV B.10). The axis is in the vertical plane during the entire shot.

[GetMeThere1]

@DrDaveBilliards : Right. There's going to be a rotation speed vs friction consideration. It's not absolute. It's a comparison between (I'll make this phrase up "angular momentum inertia") how fast a ball is spinning and how low the friction is between cloth and ball. If you played on wet ice, with balls made of thin silicon shells, it would probably be possible to apply overspin topspin right when you hit the ball, for example (if you could also happen to get good friction between ball and tip)

[GetMeThere1]

@GetMeThere1 : I'll modify that (I'm working completely on intuition here :) )

"Silicon shells with dense cores."

[GetMeThere1]

@DrDaveBilliards : Right. There's going to be a rotation speed vs friction consideration. It's not absolute. It's a comparison between (I'll make this phrase up "angular momentum inertia") how fast a ball is spinning and how low the friction is between cloth and ball. For example if you played on wet ice, with balls made of thin silicon shells, it would probably be possible to apply overspin topspin right when you hit the ball--if you could get enough friction between ball and tip.

[GetMeThere1]

@DrDaveBilliards : Also note, I said balls "can" roll on other axes. I didn't say they "must." Which happens depends on the ball-cloth friction vs the "insistence" of a heavy ball to keep rotating the way it wants to.

The big thing for me was the "rolling on less than circumferential circles." That's a mind twister :)

[DrDaveBilliards]

@GetMeThere1

FYI, I updated and added stuff to the "English-spin/slide/roll" page in the FAQ section of my website. Check it out.  It is much more clear now, with good explanations and illustrations concerning all of your questions.

Regards,

Dr. Dave

[GetMeThere1]

@DrDaveBilliards : Superb! In my mind there is NO DOUBT that your work and website represents the absolute PINNACLE of work on pool available all in one place. I'm certain that it's reputation will grow far and wide, and become known as the central clearing house for concrete, rational pool information.

[DrDaveBilliards]

@GetMeThere1

Thank you for your kind words. Thank you also for giving me a reason to improve the roll/slide section on the website.

Regards,

Dave

[GetMeThere1]

An interesting question arises from your "axis flip" video: If you put pure side english on a ball and then shoot it straight forward, will it stay purely side english, or will it tilt into follow english? Perhaps sliding friction is minimized with english (but never absent) if a rolling component is combined with the english, into follow english. Afterall, your bottom english turned into top english, only by first spending some time in a purely vertical axis.

[DrDaveBilliards]

@GetMeThere1

A ball starting out with pure sidespin and no top or bottom spin (i.e., stun) slides at first but immediately starts to develop forward roll due to sliding friction. Once full roll develops, there is no longer any sliding. At that point the ball continues to roll forward with sidespin. Both the forward speed and spin gradually slow due to rolling and spin resistance. "Draw - cloth effects" (in FAQ section) shows how the stun converts to roll.

[GetMeThere1]

Your "axis flip" demo is very interesting. It's interesting to see left draw converted to "active" left follow. But still, it demonstrates very clearly that there ARE off-horz-axis spins occurring while the ball is moving in a straight line--which, geometrically, MUST involved some "sliding."

An interesting experiment would be to make a cueball with an axle rod, SLIDE it STRAIGHT along cloth, and see if a component of off-horz spin develops.

[GetMeThere1]

And indeed, the "very small curve" at the end is in fact due to the spin slowing down enough so that the friction of the cloth can overcome the gyroscopic effect of the spin axis--thus allowing the ball to begin translating along the axis of spin (but only for a very short distance, because the now slow spin is used up almost immediately by the power needed to translate the ball along the new axis.

[GetMeThere1]

All right. At 2:25 - 2 :28 you can very clearly see the ball spinning on a non-translational axis as it's moving forward. That means the ball MUST be mostly sliding.

1) The axis in that example is not exactly equatorial. Yet it is moving translationally at very slow speed. Therefore: It IS possible for balls to slide QUITE SLOWLY while rotating in another axis--we just never see it because it's impossible to put that much spin on with a cue without giving it a good push as well.

[GetMeThere1]

....then THAT raises the interesting question for me: If you applying strong left or right draw, hit an OB, then the CB begins to draw (i.e., rotation axis is parallel to translation direction), is the original side english component then LOST at that point?? Of course, often englished draw is used to get an effect off the cushion following OB hit--but in that case, can we assume that the draw must still be "over-spinning" before hitting the rail? If not, is the side-engilsh component then lost?

[GetMeThere1]

Another way to ask this question: If a CB is moving forward in a straight line, then either it is rotating along that line and not sliding AT ALL, or else it is rotating along some OTHER axis, and sliding COMPLETELY. Is that correct?

Furthermore, then, it's weird to think what axis it's rotation on when there IS swerve, and the CB has been hit with an elevated cue (either with the intention of draw OR follow). even more.....!

[GetMeThere1]

And this relates to angular momentum/gyroscopes: when you have an axis of rotation, trying to rotate that requires an extra force (I'm thinking of spinning bicycle wheel demonstrations). That seems to imply that the ball MUST be sliding the entire way.

Is the ball completely sliding during the "hand-spinning" examples?

I'm thinking about the fact that you CAN'T achieve much draw at slow speeds conflicting with what seems like sliding here at slow speed. I guess b/c draw is working agnts frctn.

[DrDaveBilliards]

@GetMeThere1

The ball is completely rolling, with a tilted axis. There is no gross sliding at all. Although, there is rolling resistance and spin resistance slowing the ball's forward motion and spin speed respectively.

For more info, see "OB swerve and turn" under "swerve" in the FAQ section of my website.

[GetMeThere1]

@DrDaveBilliards : "The ball is completely rolling, with a tilted axis. There is no gross sliding at all." That can't be correct. A ball rolling on a tilted axis would curve greatly. Imagine an actual rod going through the ball. Hold that rod horizontally and the ball will roll in a straight line (like a car axle and wheel). Tilt that rod, and the ball will roll in a circle. To overcome the tendency to roll in a circle, the ball would have to have a "sliding" component to its motion. more...

[GetMeThere1]

@GetMeThere1 : So, if the ball is rotating off horz axis and going straight, there must be an aspect of sliding. There must be a "fight," through friction, to stop the off axis rotation and begin to roll (rotate on horz axis) vs the ball starting to roll on it's tilted axis (which would make it curve into a circle). Since the ball DOESN'T curve into a circle, that means NO COMPONENT of the tilted spin is involved in the roll--until perhaps the very end, when the dying part of tilted spin ovrcms.

[GetMeThere1]

@GetMeThere1 : Again, this can be seen in some of your hand spinning examples, where the axis of rotation of the ball can be clearly SEEN to be almost vertical--yet the ball is moving straight and very slowly. There is no "rolling" in any real sense of the word: those balls are SLIDING very slowly on the cloth, while rotating on an almost vertical axis.

[DrDaveBilliards]

@GetMeThere1

A ball moving forward slowly with lots of spin is rolling (albeit, very slowly). The ball is also spinning (very fast). In this case (e.g., a hand-spun ball), the rolling slows to a stop before the spinning does, at which point the ball remains spinning in place. As the forward motion slows, the ball can veer off course slightly, but this effect is not very strong or consistent. For more info, see "swerve - OB swerve" in the FAQ section of my website.

[DrDaveBilliards]

@DrDaveBilliards

BTW, the math and physics behind the tendency of a ball with spidespin to continue to roll in a straight line is presented in TP B.2 on my website.

[drtrotter74]

@DrDaveBilliards Makes perfect sense to me.

[DrDaveBilliards]

@drtrotter74

Me too.  :)

[DrDaveBilliards]

@GetMeThere1

"Sliding" occurs only when there is relative motion between the ball surface and the point of contact. FYI, the math and physics involved with this is covered in the first few pages of TP A.4 on my website. Once a ball develops full roll (with or without sidespin), there is no longer any "sliding" (although, rolling and spin resistance still slow both the forward motion and the spin).

[DrDaveBilliards]

@DrDaveBilliards

BTW, good descriptions and demonstrations and "sliding" vs. "rolling" can be found under "follow - normal roll" and "draw - cloth effects" in the FAQ section of my website.

[DrDaveBilliards]

@GetMeThere1

Again, when a ball is rolling forward, there is no sliding (although, there is rolling resistance due to friction, which slows the forward motion). And when a ball is spinning in place, there is no sliding (although, there is spin resistance due to friction, which slows the spin). When a ball is rolling forward with sidespin, there is a combination of both: rolling and spinning, but there is no sliding.

[GetMeThere1]

@DrDaveBilliards : I think we're at odds over the word "rolling," and therefore the word "sliding." As I'm using the words, a ball can ONLY be rolling if it's axis of rotation is horizontal and perpendicular to the direction of roll. Anything OTHER orientation must be sliding/grinding in SOME manner. If the tires on your car were rotating on some other axis, as they "rolled" forward on the roadway, they'd be worn off to the wheels in 20 miles. I call that "sliding" in SOME manner.

[DrDaveBilliards]

@GetMeThere1

Look at the "axis flip" video again. The ball is "sliding" while drag action converts draw and stun to forward roll. When there is no more sliding drag, the ball is rolling with sidespin.

I know you don't agree with these definitions, but they are standard (in pool and in physics).

Regards,

Dave

[DrDaveBilliards]

A car tire is very different from a pool ball. A tire doesn't have point contact and can't spin freely about the vertical axis. Also, the tire is cylindrical (not spherical) and is constrained by a spindle (or axle).

When a pool ball spins in place, there is "spin resistance" but no "sliding" is occurring. Likewise, when a pool ball rolls forward, there is "rolling resistance" but no "sliding" is occurring. A ball with a combo of forward roll and sidespin is also not "sliding."

[GetMeThere1]

@DrDaveBilliards : OK. There's no need to get stuck on terminology alone. I'm only saying that the moment-by-moment surface interactions between the table and the ball, when the ball is rolling by MY definition (rolling in the most simple, ordinary way) are DIFFERENT from those interactions when a ball is "rolling" with sidespin (or "angled" spin--a combination of topspin and sidespin). Will you admit that? I could be wrong, but if I am I have some REALLY hard thinking to do! more

[GetMeThere1]

@GetMeThere1 : If the ball can exhibit two different ACTIONS in two different trials while moving along the cloth (the simplest rolling vs rolling while also rotating at an axis other than the horizontal), but have exactly the same "micro-interactions" with the cloth, then....well, I simply have a VERY difficult time reconciling that with reality. Tell me that's wrong and I have some SERIOUS head scratching to do!

[GetMeThere1]

@GetMeThere1 : I actually mean "tell me that's RIGHT and I have some serious head scratching to do." IOW, well, I mean I'll be VERY confused if I'm told that, in physics, two describably DIFFERENT phenomena are occurring, but from a physics perspective, they're actually the SAME phenomenon. For example, two identical balls, rolling in identical manners, on identical cloth, at identical initial velocities, would be expected to slow to a stop after the same distance. more

[GetMeThere1]

@GetMeThere1 : But can you assure me--without needing to think about-- that two identical balls, "rolling" on DIFFERENT axes, but with identical forward velocities in space at some measuring point, on identical cloth, would be expected to stop at the same place? I don't think you can. That's all I'm saying--that their different interactions with the cloth will result in different outcomes (that is, I believe their interactions with the cloth are different).

[DrDaveBilliards]

@GetMeThere1

Visualize the "cloth interaction" when a ball is rolling with no sidespin. Then visualize the "cloth interaction" when a ball is spinning in place. When a ball is rolling forward with sidespin, the "cloth interaction" is just a combination of these two effects ... but the ball is still rolling.

[GetMeThere1]

@DrDaveBilliards : Well, as I said, I don't think either of us has an interest in fighting over a word (although I do find it disappointing that the word "roll" is carelessly defined in physics).

Answer this: Imagine that the cloth surface is inked. We know that a "normally" rolling ball will then be inked with a single line parallel with the direction of motion. What will a "rolling" ball with right topspin be inked to look like? Something VASTLY different, I'm sure...more

[GetMeThere1]

judging by your flip video, after the flip, when rolling with top and english, the inked line would be along a DIFFERENT axis than the direction of forward movement of the ball.

Another one: Imagine "motorized tongs" that you could hold and set a ball spinning. Then put that spinning ball down with the axis of spin in any plane but horz. It would roll in a curved path. The same ball hit with a cue, however, goes straight. There must be extra energy used in that conflict of forces.

[DrDaveBilliards]

@GetMeThere1

When a ball is rolling (w/ or w/o sidespin), the trace an inked surface would mark on the ball is a circle. If the ball is rolling with no sidespin, the circle is vertical and goes around the full circumference of the ball. If the ball is rolling with sidespin, the circle is smaller and tilted. With more sidespin and/or less forward speed, the circle is smaller and more tilted.

continued ...

[DrDaveBilliards]

@DrDaveBilliards

A ball with lots of spin and very little forward roll would trace a very small circle.

A ball spinning in place traces a point (the smallest possible circle).

Again, every "rolling" ball traces a circle, and as the spidespin wears off, the circle size and tilt angle change.

[GetMeThere1]

To clarify: I'm talking about the shots between times 0:37 - 1: 10. It SEEMS very clear that, after hitting the rail, the CB is undergoing pure roll (i.e., axis of rotation = direction of translation). HOW does the ball "move" before hitting the rail, though? If it's truly rotating on a 2-10 axis (clockface values), then to travel in a straight line requires "pure" skidding motion in a straight line. How could that really happen/work? more...

[DrDaveBilliards]

@GetMeThere1

A ball rolling with sidespin is not skidding at all ... it is rolling with a tilted axis.

Now, when you hit the CB with a cue, it will slide (and swerve, if there is sidespin) before rolling is established. However, with the examples in the video, where the cue is as level as possible and above-center hits are used, the CB develops roll very quickly (e.g., within 1-2 inches).

[GetMeThere1]

What is the actual axis of rotation of the balls in your cued balls examples at the start of the video? If the balls appear to roll straight, then either the axis of rotation is parallel to the direction of translation (I hope I'm saying that right--you know what I mean), or else the axis of rotation is some OTHER axis (such as the axis you actually hit it on--say about 10 o'clock to 4 o'clock, for left-top english), and then the CB is TOTALLY sliding. Difficult to picture/understand.

[DrDaveBilliards]

@GetMeThere1

When a CB is rolling forward, with no sidespin, the axis of rotation is horizontal.

If a CB is spinning in place, with no forward roll, the axis of rotation is vertical.

When the CB is rolling forward with sidespin, the axis of rotation is at an angle (between vertical and horizontal).

For more info, see "spin axis flip demonstration" under "English" in the FAQ section of my website.

[mrdeathwillkillyou]

How does he make the ball go straight with  side spin? this is my main problem in pool and i cant figure it out.

[stevesp101]

The side spin by itself does not curve the path of the cue ball at all. However, if you hit the ball with a completely level cue and side spin combined with topspin, that actually does curve the cue a little bit. It has sort of the opposite effect as the draw/masse shot--top left makes the ball go left and then curve back right (whereas bottom left makes the ball go right and then masse left). Jack Koehler discusses this phenomenon in his books (specifically the Science of Pocket Billiards).

[DrDaveBilliards]

The focus of the video is a rolling CB. Swerve (masse type curve) occurring while the CB is sliding is a different effect.

BTW, to get reverse swerve, as you describe, the cue actually needs to be tilted below level (with the butt lower than the tip).

Dr. Dave

[stevesp101]

I know that masse is a different effect, I only mentioned it as a point of reference for what I was talking about with reverse swerve as you call it. I've been looking but can't find any literature on this except in Koehler's book. He says that in order for the ball to curve the cue needs to be hit level with top side (p. 76). But I cannot find anything online to corroborate or dispute that. Do you know of anyone else who discusses this? And thanks for taking the time out to respond.

[DrDaveBilliards]

i don't think his statement is correct. The physics shows (e.g., see TP A.19 on my website) that slight upward cue elevation (with the butt on the table and the tip up) is required to create reverse swerve.

I don't think it is mentioned much (e.g., in books), because it is not a practical or useful effect (except maybe in trick or proposition shot).

Regards,

Dr. Dave

[stevesp101]

Alright, I guess the only way to be sure is to try it out then. Thanks for the tips and the videos.

[BartjeOstend]

interesting movie. Thanks

[craigaosborne]

i prefer snooker to pool but hey nice video. it might be worth noting that the slower the cue ball is moving when it his the cusion (bank) then the more reaction is

[signmaint]

Nice video but I have a question. Are graphite cues better than wood cues?

[DrDaveBilliards]

Most pros and good players prefer wood cues.

Dr. Dave

[mongrelsoldier]

Graphite cues are, for lack of a better phrase...complete shit. Stick to wood. Graphite/ Fiberglass cues just get sticky.

[kolaas2006]

It seems to me that backspin plus sidespin does give a curve. Is that true? For tiny swirves I play a ball with draw-sidespin and that usually gives me a 1 or 2 cm curve. I do that with a nearly leveled cue.

[DrDaveBilliards]

That's true; but after the swerve takes place, the ball heads in a straight line with sidespin.

Dr. Dave

[fragkid1]

lol sad

[currants007]

thanks alot

[DrDaveBilliards]

You're welcome a lot.

Dr. Dave

[michealcrehan]

you're videos are really benefical. Thanks from Michael in Ireland. keep posting.

[DrDaveBilliards]

Thanks.

Dr. Dave