throw

• answers to questions about CIT, SIT, and OE
• cling
• draw and follow effects
• examples
• "hold" or "kill" shot to limit cue ball drift
• maximum throw
• physics details and results
• spin transfer
• stop shot with English
• using outside English to prevent throw and cling

for more information, see Section 4.04 in The Illustrated Principles of Pool and Billiards

answers to questions about CIT, SIT, and OE

How do you know which way the object ball will throw for different types of shots?

Throw direction depends on the direction of the relative motion of the surface of the cue ball in contact with the object ball. This direction is affected by both cut angle and spin. I think my January '07 and February '07 articles illustrate the different possibilities quite well.

See also:

• squirt, swerve, and throw confusion
• HSV B.18 - spin-induced throw speed and English effects
• HSV B.30 - cut-induced and spin-induced throw and spin transfer
• HSV B.33 - outside English gearing, and cut and spin-induced throw
  

Do CIT and SIT add or subtract as independent factors?

Object ball throw depends on cut angle, shot speed, type and amount of English, and the amount of vertical plane spin (draw, follow, stun). My series of twelve articles on throw elaborate on all of these factors. Collision-induced throw (CIT) and spin-induced throw (SIT) are just different names for throw, depending upon the primary cause of the throw, but the effects don't really combine as separate factors.

Outside English (OE) can diminish, eliminate, or even reverse the direction of throw. But at larger cut angles, a small amount of OE can actually increase the amount of throw (e.g., see Diagram 1 in my February '07 article). Again, the reason has to do with the relative surface speed between the balls. Sliding friction (and therefore throw) is greater at slower relative surface speeds. With larger cut angles, inside English (IE) increases the relative surface speed between the balls and reduces the amount of friction and the amount of throw (see the diagram). For a large cut angle, a small amount of OE can reduce (but not reverse) the surface speed some resulting in more friction and more throw.

With "gearing outside English" (gOE) there is no sideways force whatsoever. That's why there is no throw. The OB heads exactly in the impact-line direction (i.e., in the ghost-ball line-of-centers direction). There can be throw only when there is a sliding force between the CB and OB. With gOE there is no sliding between the balls during contact (see my January '07 article). With less-than-gearing OE, throw is in one direction (the CIT direction); and with more-than-gearing OE, throw is in the other direction (the SIT direction). There either is throw or there is not, and it can be in one direction or the other. GOE completely eliminates throw and cling. It's just tough judging the exact "gearing" amount of OE you need for each cut angle.

cling

What is cling?

With new, clean, and smooth balls, the amount of throw will be less as compared to other ball conditions. An exception is when a chalk smudge happens to appear exactly at the contact point between the CB and OB. In this case, the amount of throw will be much greater than normal. This effect is called “cling” (AKA “kick” or “skid”). The frequency of cling (excessive throw) will usually be worse with old, dirty, and/or rough balls. Also, on cloth that is new, thin, and slick, cling might occur more often, because chalk smudges on the CB might tend to wear off less easily. What might make this effect even more noticeable is if the balls also happen to be new, clean, and/or polished (e.g., which might often be the case with televised tournament conditions). Because the amount of throw is less with these ball conditions, when cling does occur, it can be strikingly noticeable. Anytime you see chalk smudges on the CB, you should wipe them off (or ask for a referee to wipe them off if you are in the middle of a tournament game). We have enough reasons to miss shots as it is without having to worry about excessive and unpredictable throw due to cling."

draw and follow effects

Do shots with draw and follow throw as much as shots with stun?

Stun shots exhibit the most cut-induced throw (see my September '06 article) and spin-induced throw (see my November '06 article). Draw and follow shots exhibit less throw (see my October '06 article); and if they have the same amount of bottom or top spin, the amount of throw is the same (and less than the amount of stun throw). See my October '06 article to see how stun, follow, and draw shot throws compare. Because bottom spin wears off due to "drag" action, many draw shots will have less spin, and more throw, than typical follow shots.

Now, object ball (OB) swerve does have a slight effect on throw with follow and draw, but the effect is very small (see the end of TP A.24 for example numbers). Strictly, a follow shot will have slight OB swerve in the throw direction, effectively increasing the effective throw a tiny amount; but for all practical purposes, follow and draw shots with equal amounts of spin throw the same amount. Now, if a draw shot has more backspin than a follow shot has topspin, then the draw shot will definitely have less throw than the follow shot. The closer a shot is to stun, the more throw it will have.

examples

What are some example shots where throw and spin transfer can be used or must be accounted for?

Here are some:

• NV 4.15 - Using throw to make a partially blocked shot
• NV 4.16 - Over-cutting a cut shot to compensate for throw
• NV 7.5 - Frozen ball throw
• NV 7.6 - Frozen cue ball throw
• NV A.18 - Colin Colenso's throw test video (effects of speed and English)
• NV A.21 - Bank shot using throw and spin transfer

I also show and describe examples in my series of 12 articles on throw.

"hold" or "kill" shot to limit cue ball drift

Can throw be used to "kill" cue ball motion on a cut shot?

(TP A.29) presents a full analysis, with illustrations and plots, that explains one of the reasons why cue-ball-to-object-ball distance makes a big difference in the ability to kill cue-ball motion on a cut shot. Other reasons related to drag control and swerve are also described in my July '07 instructional article.

I hope some of the throw non-believers out there will try Bob's test. At small distances with slow-speed stun, with about 50% English, the effect of throw is irrefutable and dramatic.

maxiumum throw

How can I achieve maximum throw using English?

See HSV B.18. Maximum spin-induced throw (SIT) occurs with slow speed and about 50% English. See my December '06 article for more information.

Maximum collision-induced throw (CIT), with no English, occurs at about a 1/2-ball hit. See my September '06 article for more information.

physics details and results

What are all of the factors that affect how much throw a shot will have?

TP A.14 contains a thorough analysis, and TP A.28 contains graphs for all types of shots. Let me warn you ahead of time: TP A.14 is full of lots of complicated math and physics, so you might not want to look at the whole thing, but the results in TP A.28 might still be of interest. If not, or at least look at some of the conclusions summarized below. Plots in TP A.14 compare well to experimental, theoretical, and qualitative results presented by Marlow, Sheppard, Koehler, and Jewett. The analysis and results cover both collision-induced throw (CIT) and spin-induced throw (SIT). The effects of cut angle, speed, and spin are also considered.

The model of friction I use is more complete and accurate than any other I have seen presented before. First, I include the effect of speed on friction, based on experimental data from Marlow. And more importantly, I correct an error that appears in many analyses of collisions with friction (e.g., in Shepard's work). The error involves not taking into account the potential loss of relative sliding motion between the CB and OB during impact. I have accounted for this effect, and it significantly affects the results.

Here are some of the conclusions resulting from the mathematical analysis (which agree with what most people understand about throw effects)

• Both CIT and SIT are larger at slower speeds.
• CIT increases with cut angle, but levels off at higher cut angles.
  
• CIT is larger for stun shots.
• CIT is larger for stun shots close to a 1/2-ball hit (30-degree cut angle), per the plot on page 6.
• SIT is maximum for stun and a medium amount of sidespin, per the plot on page 7. "Medium" corresponds to 50% English. Additional sidespin does not result in more throw; in fact, the model predicts a loss in throw with excess sidespin, because friction is less for higher relative speeds between the balls.
  
• SIT is larger, and most sensitive to sidespin, with stun shots. But SIT is not nearly as sensitive to small amounts of sidespin as some people think. The more accurate model of friction affected these results significantly.
• Inside English increases CIT, especially at small cut angles.
• Outside English can create SIT that overcomes CIT.
• Outside English creates maximum SIT at small cut angles.
• "Gearing" outside English results in absolutely no throw.
• The theoretical plot of throw vs. cut angle for stun shots matches up with Bob Jewett's experimental data very well (see my September '06 article).
• For a stun shot, the amount of CIT is independent of speed at small cut angles.
• For a stun shot, CIT is largest in the half-ball hit range (30-degree cut angle range).
• For a stun shot, at larger cut angles, CIT is larger for slower speeds.
• For a half-ball hit, throw is greatest for a stun shot with no sidespin or with 10% outside English. For 50% outside English with a half-ball hit, there is no throw.

spin transfer

Can you prove to me that spin can be transfered from the cue ball to an object ball?

For the non-believers out there, I now have several resources available to prove that spin transfer exists. HSV A.66 provides a high-speed video demonstration of the effect. NV A.21 and NV B.20 provide demonstrations of a bank shots not possible without spin transfer. And for the physics nerds out there, TP A.27 provides a mathematical proof.

HSV A.143-A.146 illustrate spin transfer and "vertical throw" (ball hop) resulting from follow and draw. Notice how the effects are much greater when chalk is added to the object ball surface. Remember: keep those balls clean.

If the non-believers in the congregation are still skeptical, the only thing else I can do is ask you to just have faith. Spin transfer does exist, and it can affect pool shots.

For more information, see HSV B.30 and my March '07 article. Whenever there is throw, there is spin tranfer; and the more throw you have, the more spin transfer you have.

from Bob_Jewett:
...we have been discussing two impossible shots, a cross-side bank shot and a rather tough spot shot.

In the bank, the cue ball is frozen to the side cushion on the line, and the object ball is frozen to the same side cushion just the other side of the side pocket. The shot is to bank the object ball one-cushion cross-side.

In the cut shot, the object ball is on the spot. The cue ball is near one foot pocket. The shot is to cut the object ball into the other foot pocket. The cut angle is more than 90 degrees.

[Here's the] Vernon Elliott's bank shot: http://www.youtube.com/watch?v=vEyCQSN8qU0

[Here's the] impossible cut shot: http://www.youtube.com/watch?v=uHf3o6FtNnQ

stop shot with English

How do you account for throw with a stop shot with English?

To stop the cue ball using side English, there must be a cut angle. In other words, the cue ball must hit the object ball slightly off center as if you were going to "cheat" the pocket (e.g., see NV 5.7). If you are aiming the shot straight-on, cue ball deflection (squirt) will automatically create the cut angle (see NV 4.13 for a description and illustration of squirt). With a cut angle, if there was no English the object ball would cheat the pocket and the cue ball would drift along the tangent line. With left English, squirt causes the cue ball to deflect to the right, creating a cut angle to the left. However, the object ball would be thrown back to the right (due to the left English) towards the center of the pocket. Because the cue ball throws the object ball right, the object ball pushes back on the cue ball to the left, counteracting the expected tangent line motion to the right. Therefore, the cue ball stops in place. My May '05 instructional article doesn't address this issue directly, but the information is relevant. Check it out.