Sidespin on a stopshot

[Tennesseejoe]

I think that depends on how much squirt your stick has. A typical house stick might be parallel.

Thanks for the quick reply. I was trying to edit this to include deflection sending the cueball to the left. If it is deflected tothe left--would it really be a full hit?

 

[Jal]

If the cueball is going straight, i.e. not curving, at the moment of impact then I can't imagine an instance where the ball will move more than an inch. You figure that if the cueball moves an inch then the object ball is going to move by 5 or 6 inches with in a 4-5 foot shot!

Let's imagine that neither the cueball or object ball have any forward speed after the collision. In this case, both balls will move an equal distance sideways before coming to a stop (ignoring spin interaction with the cloth). In reality, with forward speed considered, the object ball will travel farther to the side if it is allowed to move until it comes to rest. This is because the friction force is not acting as directly sideways compared to the cueball, because of the much greater forward speed of the object ball.

Based on the amount of throw that occurs, I believe the 1" - 4" figures are correct, for 100 speed cloth. But I'll admit, I'm feeling a little queasy about it in that I haven't figured out just how much the cueball will curve from its spin.

In your example of a 4-5 foot shot, I don't know how you arrived at the 5-6" movement?

Jim

 

[Bob Jewett]

.. .. If it is deflected tothe left--would it really be a full hit?

Whether it's a full hit or not does not depend on the cue stick. It only depends on the path of the cue ball just before it hits the object ball. The direction of that path must be towards the center of the object ball. That's how we've defined a full hit for this question, I believe.

 

[zeeder]

In your example of a 4-5 foot shot, I don't know how you arrived at the 5-6" movement?

Jim

If the force of the spin/throw is enough to move the cueball 1" then the object ball will be thrown the same amount which would be magnified over 4-5'. This is, of course, assuming that the only source of the lateral movement of the cueball is the friction from the spin.

The basic point I was trying to get across was that if your object ball was a decent distance from the hole and you aimed for the center of the pocket on a straight in shot and the cueball moved 1" laterally due to spin that you'd miss the ball by a lot!

 

[Tennesseejoe]

Whether it's a full hit or not does not depend on the cue stick. It only depends on the path of the cue ball just before it hits the object ball. The direction of that path must be towards the center of the object ball. That's how we've defined a full hit for this question, I believe.

I agree. My thought was that it would not be a full hit and I wrote why it wouldn't and didn't finish the thought.---Sorry.

 

[unknownpro]

I think that for inside english, you are already used to compensating for collision-induced throw so the added (if any) throw from the inside english is smaller.

That makes no sense to me.

In fact, if Marlow and Alciatore are right, and friction decreases with increasing slip speed, inside english could conceivably reduce throw below the amount due to collision-induced throw.

That's what I'm saying. It is a fact that two sliding bodies have less friction between them than two at rest. And it seems to me more spin equals less throw on inside english shots (less than collision induced center ball throw), and more on outside.

As for whether throw is significant on most shots, I think it is. And I think most people adjust for it subconsciously and just do what feels right to put the ball in the pocket.

Yeah, it's significant on a lot of shots. Most people play totally subconsciously, they get in stroke and don't know how they did it because the only way they can do it is by not looking at the wrong things they usually are looking at when they can't make a ball.

unknownpro

 

[Jal]

If the force of the spin/throw is enough to move the cueball 1" then the object ball will be thrown the same amount which would be magnified over 4-5'. This is, of course, assuming that the only source of the lateral movement of the cueball is the friction from the spin.

The basic point I was trying to get across was that if your object ball was a decent distance from the hole and you aimed for the center of the pocket on a straight in shot and the cueball moved 1" laterally due to spin that you'd miss the ball by a lot!

Zeeder, thanks for the explanation.

I arrived at the 1" number with throw values of 2 degrees for a very slow shot (3 mph) and 0.6 degrees for a fast shot (10 - 12 mph). These are from Dr. Dave Alciatore's analysis of throw (same equations) and are for a near maximum tip offset (2/5 R). This is not too much throw as throw goes, which can be up to around 5 degrees under normal circumstances. For the high speed shots, you're unlikely to miss at four feet unless you're aiming at the edge of the pocket to begin with. But certainly two degrees of throw can easily be enough without any adjustment for it.

In other words, the amount the object ball moves sideways after contact doesn't really correlate with the amount of sideways drift of the cueball ball since the object ball either gets pocketed or hits the cushion long before it comes to a rest. The cueball, on the other hand, does roll all the way to a stop. Surprisingly, for this range of speeds (3 - 12 mph) and this tip offset (2/5 R), the cueball always seems to move over by about an inch (if the throw theory is correct and nothing funny happens on the cloth).

Jim

 

[Bob Jewett]

I think that for inside english, you are already used to compensating for collision-induced throw so the added (if any) throw from the inside english is smaller.

That makes no sense to me.

...

Suppose you want to cut the object ball 30 degrees with a center-ball shot (no follow or draw or english). To get that cut angle at medium speed, you have to set up for a fullness of hit of about 33 degrees to compensate for the collision-induced throw (of about 3 degrees). Adding inside english and will not increase the throw much. This makes it seem that inside english is less effective, but at fuller cut angles, it becomes more important.

It is a fact that two sliding bodies have less friction between them than two at rest.

But the effect that Marlow and Alciatore consider goes beyond that. If two surfaces are sliding past each other, there is less friction for faster sliding. On the shot without english above, the surfaces during contact are slipping. If you add inside english, they are just slipping faster. A lot of people would guess exactly the opposite, that you should always get more throw with more side spin, but that seems not to be what the balls really do.

In the simple treatment of sliding friction, the coefficient of friction is assumed to be indepent of both the speed of slipping (as long as there is some slipping) and the force pressing the surfaces together. That's the way I learned it in high school. It seems that both speed and pressure change the coefficient of sliding friction.

 

[pete lafond]

Suppose you want to cut the object ball 30 degrees with a center-ball shot (no follow or draw or english). To get that cut angle at medium speed, you have to set up for a fullness of hit of about 33 degrees to compensate for the collision-induced throw (of about 3 degrees). Adding inside english and will not increase the throw much. This makes it seem that inside english is less effective, but at fuller cut angles, it becomes more important.

But the effect that Marlow and Alciatore consider goes beyond that. If two surfaces are sliding past each other, there is less friction for faster sliding. On the shot without english above, the surfaces during contact are slipping. If you add inside english, they are just slipping faster. A lot of people would guess exactly the opposite, that you should always get more throw with more side spin, but that seems not to be what the balls really do.

In the simple treatment of sliding friction, the coefficient of friction is assumed to be indepent of both the speed of slipping (as long as there is some slipping) and the force pressing the surfaces together. That's the way I learned it in high school. It seems that both speed and pressure change the coefficient of sliding friction.

When I use inside english I am minimizing throw, when I use outsided I am maximizing throw. It just works and the effects are generally based upon feel of playing conditions - how the last shot moved. Speed will also minimize and again this changes by playing conditions as well.

However, most shots we learn to make are the result of experience, not through uinderstanding physics. The cloth, balls and humidity are all important variables that we intuitively adjust to. It all changes except ....

There is one shot that seems to remain consistant which is the medium slow roll, no matter the english. I do not know how to express this shot except that it is the same shot we use when there is an inevitable scratch in the side pocket and we want to drift the CB past it without scratching. It is also the same shot speed we play as seen below where the CB needs to drift sharply to play the 7 ball.

START(
%FO2Z1%GD9R0%HD4Y3%IO4W6%P\5R7%WQ2Y8%X[6S2%[E2[1%\N2Z2%]E7X1
%^N3Z4%eC5a4
)END


Even though this shot is using inside english that would negate throw, I just needed a shot that describes the CB speed and roll I am referring to (clearly we mentally ajust even to this speed based on condtions and felt). If I used OE with this CB speed and drift I will not get any throw, period. This shot does not throw plus the OB and OB/CB deflections are truer. Why does this shot react differently? It is because there is no CB curve?

 

[Cornerman]

Suppose you want to cut the object ball 30 degrees with a center-ball shot (no follow or draw or english). To get that cut angle at medium speed, you have to set up for a fullness of hit of about 33 degrees to compensate for the collision-induced throw (of about 3 degrees). Adding inside english and will not increase the throw much. This makes it seem that inside english is less effective, but at fuller cut angles, it becomes more important.

But the effect that Marlow and Alciatore consider goes beyond that. If two surfaces are sliding past each other, there is less friction for faster sliding. On the shot without english above, the surfaces during contact are slipping. If you add inside english, they are just slipping faster. A lot of people would guess exactly the opposite, that you should always get more throw with more side spin, but that seems not to be what the balls really do.

In the simple treatment of sliding friction, the coefficient of friction is assumed to be indepent of both the speed of slipping (as long as there is some slipping) and the force pressing the surfaces together. That's the way I learned it in high school. It seems that both speed and pressure change the coefficient of sliding friction.

I'm sure I said this in internet career post #3723 (along with its corollary).

Fred

 

[enzo]

36 to 40 a tie?? in sports no, in science, maybe??

ok, just for laughs, i have a silly question for Jewett-Mike and Co.

Is the 36 to 40 vote in this thread statistically significant at a p-value of 0.05?? I could probably figure it out myself if i got one of my old stat-books out, but i refuse to do stats again, lol.

i would think, of course, that it is not significant just by glancing at the numbers. so, effectively, the poll (albiet a very biased one), was a dead heat.

 

[TheConArtist]

using BHE i can make it stop and just spin using PE i can get it to go left a little so i can't vote LOL,

 

[Bob Jewett]

ok, just for laughs, i have a silly question for Jewett-Mike and Co.

Is the 36 to 40 vote in this thread statistically significant at a p-value of 0.05?? I could probably figure it out myself if i got one of my old stat-books out, but i refuse to do stats again, lol.

i would think, of course, that it is not significant just by glancing at the numbers. so, effectively, the poll (albiet a very biased one), was a dead heat.

The sigma for sampling N items of probability p is about sqrt(N*p*(p-1)) or sqrt(76/4) or about 4. It looks like a tie so far.

 

[mikepage]

The sigma for sampling N items of probability p is about sqrt(N*p*(p-1)) or sqrt(76/4) or about 4. It looks like a tie so far.

Let's see. We have a poll with a red choice and a blue choice, and while the red and blue bars are about the same length, blue is slightly longer. By established precedent, that means red won.

Significantly though, if the poll was taken over again with people knowing what they know now, I believe many of the red responders would change ships and choose the blue response, known as "move slightly to the left."

Oh, and I think the same would be true for the "sidespin on a stopshot" poll.

mike page
fargo

 

[enzo]

Same Subject, NEW THOUGHT....

Ok, now that we have determined that the cueball does in fact move slightly on a 100% full hit with english (at least in my mind), I'd like to explore the question that compelled me start this thread.

If you own Freddy's Banking Book, "Banking with the Beard," you'll notice that on MANY occasions he says to make this bank, hit the ball full in the face with one tip of left (or 2 tips or whatever).

Now, does he mean an actual stopshot (ie stopping the cueball; if you haven't read this thread, stopping the cb with english requires you to cut the ball slightly), or does he mean hit it full in the face with one tip of left and a natural occurrence will be for the cueball to move left slightly?

Any clarification appreciated.

 

[unknownpro]

Ok, now that we have determined that the cueball does in fact move slightly on a 100% full hit with english (at least in my mind), I'd like to explore the question that compelled me start this thread.

If you own Freddy's Banking Book, "Banking with the Beard," you'll notice that on MANY occasions he says to make this bank, hit the ball full in the face with one tip of left (or 2 tips or whatever).

Now, does he mean an actual stopshot (ie stopping the cueball; if you haven't read this thread, stopping the cb with english requires you to cut the ball slightly), or does he mean hit it full in the face with one tip of left and a natural occurrence will be for the cueball to move left slightly?

Any clarification appreciated.

I'm sure Fred knows that when you hit it full in the face the cueball will stop dead, lol! I doubt he intends that you cut the ball to the right just so you can throw it further left with english.

unknownpro

 

[mikepage]

Ok, now that we have determined that the cueball does in fact move slightly on a 100% full hit with english (at least in my mind), I'd like to explore the question that compelled me start this thread.

If you own Freddy's Banking Book, "Banking with the Beard," you'll notice that on MANY occasions he says to make this bank, hit the ball full in the face with one tip of left (or 2 tips or whatever).

Now, does he mean an actual stopshot (ie stopping the cueball; if you haven't read this thread, stopping the cb with english requires you to cut the ball slightly), or does he mean hit it full in the face with one tip of left and a natural occurrence will be for the cueball to move left slightly?

Any clarification appreciated.

We've spent a lot of time talking about how the cueball will move slightly to the left on a full hit with left sidespin, and the people who understand this stuff voted for that in the poll. ;-)

But now that I see the reason for your question, I have a practical response. What we talked about is a small and subtle effect. In the context of your question, it's more academic than anything else.

I would say it doesn't really matter what he means. He may not even know or care which of these he means. The much bigger effect and the one of practical concern is that the sidespin will alter the angle of the object ball off the cushion.

mike page
fargo

 

[jjinfla]

Zo,
I think the real question is why on earth we would care??

Because it looks so nice in Bob Byrne's video. Either vol 1 or 2 or maybe both of them had it in the beginning when he was doing tricks in the leader.

If the CB moves left then you did not hit perfectly straight on the 180° line.

Jake

 

[Tennesseejoe]

Because it looks so nice in Bob Byrne's video. Either vol 1 or 2 or maybe both of them had it in the beginning when he was doing tricks in the leader.

If the CB moves left then you did not hit perfectly straight on the 180° line.

Jake

Unless you put left English on the cue ball.If the cue ball hits the object ball in a straight line and the cue ball has left English---the cueball will go left and the object ball will go right.

 

[Banks]

My 39 cents

I'm going out on a limb here, but I don't believe anybody ever mentioned how much force was or could be used for this hit. At a slower hit, or using far left/right english, there is going to be much more grab between the cb and ob. I believe the answer is both, depending on how the cb is struck. Practicing banks with spin from the kitchen I think I've seen both happen.

Maybe the cb movement was too little to notice or maybe the cb was off a little and countered the movement from spin, but I still think both can be done.

My weak theory on the physics would be.. if the cb is struck harder, the contact is very brief and therefor has much less time to grab the effects of the spin, leaving the cb to spin helplessly in place. If you're not very far over left/right, this makes it even more easily done.