stroke Dr. Dave's answers to frequently-asked questions
(FAQs),
mostly from the BD
CCB and AZB
discussion forums
maintained for the book: The
Illustrated Principles of Pool and Billiards
and the monthly Billiards
Digest "Illustrated Principles"
instructional articles
for more information, see Section 2.05 in The Illustrated Principles of Pool and Billiards
How does the acceleration of the cue vary during a typical stroke?
Accelerometer measurements and description of cue stick reactions during strokes and object ball impacts can be found in TP A.9. The blue curves in the top three plots (red curves in the bottom two plots) represent forward acceleration. A positive acceleration implies slowing in the backward direction (e.g., at the end of the back swing) and/or speeding up in the forward direction (e.g., during most of the pre-impact portion of the forward stroke). A negative acceleration implies slowing in the forward direction (e.g., in the later part of the forward warm up strokes) and/or speeding up in the backward direction (e.g., at the beginning of the backstroke).
I think the relatively flat portion of Andreas' curve, before impact, corresponds to the second half of his back-swing. Notice how it is nearly identical to the shapes in the warm-up strokes (which I think are fairly firm). I think the entire forward stroke, before impact, is represented by the tall peak. The final forward stroke is much faster and more forceful than the warm-up strokes. After the peak, and before impact, the acceleration appears to go negative a little, implying he was actually decelerating a little before impact (if you trust the sensor, its calibration, and the data acquisition). At impact, the signals go wild due to shock waves and vibration.
In the first two plots (softer strokes), the acceleration is still positive at impact, implying that the cue stick is speeding up during the entire forward stroke (e.g., he is accelerating into the ball). Both of Pizutto's plots show slight slowing (negative acceleration) just before impact.
Andreas does not appear to have a distinct pause at the transition between the back and forward stroke because the acceleration curve would be flat (at zero) if there were a deliberate pause.
The spike before impact represents the entire forward stroke, not any weird wrist action. Note that the time scales are very different between the two sets of plots. Pizutto's plots are just showing the final forward stroke and the resulting shock and vibration immediately after impact. Andreas' plots show a much large time interval, including warm-up strokes.
Are there any plots from high-speed video showing how a stroke's speed typically varies with distance?
Yes. Bob Jewett has an article with a good example plot
(see page 9 here).
What are considered the "best practices" for stroke mechanics?
My stroke "best practices" document summarizes the generally-accepted technique advice. My fundamentals "best practices" check-sheet is also useful to help diagnose possible problems with mechanics. These and other useful documents can be found in the Instructor and Student Resources section of my website.
What are considered "best practices" for the stance?
from
av84fun:
There is no such thing as an "ideal stance" for everyone.
There is what I would call a "classic" stance...that which is recommended
in most texts dealing with the subject which are, in turn, based on the stances
used by a large number of top players.
That "classic stance" might be described as:
1. Placing the back foot on the extended line on which the CB will be directed toward the OB.
2. Place the front foot at about a 45 degree angle to that line.
3. Bend forward with a RELATIVELY straight back leg onto a bent forward leg.
4. Place the cue directly under the chin.
5. In the SET position, with the tip very close to the OB, the forearm should be at a right angle to the CUE.
The variations from "classic" are nearly endless but frequently would include.
1. Instead of a nearly straight rear leg, both legs are bent in a partial "squat" type of stance...watch Strickland who does this.
2. The Brits tend to adopt more of a snooker stance where the forward let is placed at a wider than 45 degree angle which, in turn, "squares up" the chest toward a more perpendicular orientation to the line toward the OB.
3. The chin is moved to various positions to the outside (away from the body) of centered under the chin.
Finally, various chin heights (above the cue) are used. Back in the day, the chin was help several inches above the cue but today, many pros have moved the chin much lower...Allison's cue rubs back and forth ON her chin.
from dr_dave:
The amount of leg spread
also varies a lot from one person to the next based on the person's height, flexibility,
chin height above the cue, body shape and anatomy, and comfort level. The photos
in my document are of a top regional player. I also prefer a wide foot stance
because of my height (6' 3") and desire to get my head low without too much
strain on my lower back and neck. As with most stance, grip, and bridge related
issues, individual comfort is a primary consideration.
Is it recommended to drop one's elbow during the stroke?
I think there is a lot of misunderstanding and misrepresentation in the "elbow drop" arena. But it is my understanding that the general "don't drop the elbow" advice is not as rigid as some people think. Obviously, for an extreme power shot, the elbow will want to drop naturally during the follow through (due to the momentum of the arm and stick). The problem lies with dropping the elbow when it is not intended, especially if the elbow is dropped before cue ball contact. For most (almost all) shots, and for most people (especially beginners), accuracy and consistency will be better if the elbow is not dropped before (or after) cue ball contact. The problem with dropping the elbow after cue ball contact (e.g., when it is not required based on shot power) is that if one's timing is a little off, the elbow might drop a little before contact, which can affect CB contact point accuracy. I think that is the main point the non-elbow-drop instructors try to make. Hopefully, they will correct me if I have misrepresented their philosophy.
Here's a good
video
demonstration of a non-elbow-drop stroke.
from Bob_Jewett:
...the
vast majority of players drop their elbows some on power shots. When talking "elbow
drop" you need to be clear about how much. Many players drop their elbows
only about the thickness of their upper arm on most power shots.
Two articles
that discuss elbows and the strange things people do with them are:
http://www.sfbilliards.com/articles/2004-02.pdf
http://www.sfbilliards.com/articles/2004-03.pdf
For most of the players I've checked, there are some shots for which their elbows do not move.
from pooltchr:
...the vast majority of students who
come to me are looking for consistency. The best way to achieve this is SPF and
no elbow drop. There are select shots where dropping the elbow may allow more
power, but that same majority would be giving up a lot of accuracy to gain the
power. In my opinion, accuracy is more critical than power. There are always going
to be players at the top of the game who can control a full arm stroke with accuracy
and consistency. They would be in the minority.
I have had very good success helping students improve their control by using the pendulum stroke. As an instructor, I have to consider each student as an individual, so I can't say I would ever say that a student MUST not drop their elbow. But so far, whenever I have had a student try the pendulum stroke, they have shown very quick improvement in accuracy. I have one student who uses this stroke on his break! He regularly makes something (often multiple balls) and almost always lands the cue ball in the center of the table. I don't see any reason to introduce a full arm swing to a player who would be better served from an accuracy standpoint by developing a simpler motion. When the student comes to me who can consistently make controlled contact with a full arm stroke, I don't think I would suggest any changes. Until that student appears, I think this is the best method to teach. There are going to be exceptions, but I suspect they are few and far between.
Does an extended follow-through add power to a shot?
I think this is a question of cause and effect. A follow-through strictly has no influence on the cue ball because the cue tip is in contact with the cue ball for only a very short amount of time (approximately 0.001 seconds). The only things that significantly affect the breaking power for a given cue stick are cue stick speed at impact and tip offset (distance away from a center ball hit). However, if a powerful stroke does not exhibit a big follow-through, it is either not very powerful, or effort is being made to limit the follow-through. If one tries to constrain the follow-through, one will probably not achieve maximum speed at impact. Many authors and instructors recommend trying to "accelerate through the ball" for power shots. This thinking often helps one create good power, and it results in significant follow-through.
Follow-through can also be important in achieving good action on draw shots (although, not always for the reasons people think). For more info, see my May'06 instructional article. In particular, see item "b" under "other advice" and item "5" under "stroke best practices." I think these points apply equally well to both a power break and a power draw.
All
the cue ball cares about is tip contact point, cue speed, and cue elevation at
the moment of impact. Follow-through is just a symptom of your stroke and has
no direct affect on the action of the shot. Now, when you follow through, maybe
you are doing something different with your stroke to get a different cue speed
or a different tip contact point, or maybe your stroke is straighter. You might
want to videotape your stroke changes and look at the chalk mark on the CB. It
helps to use a ball with markings (e.g., a striped ball or a Jim Rempe ball) when
checking the chalk mark. If two shots have the same cue speed and tip contact
point, but have different amounts of follow through, the action of the shots should
still be the same. If you are getting different action, you are not hitting the
CB with the same speed, tip-contact point, or aiming line.
What is SPF or SPFF?
from Scott_Lee:
The "set" position
occurs at the CB, after your warmup cycle is finished. It's the last conscious
thought about, "Well? Are you ready or not?" With the tip at the CB,
the "set" position is used to verify earlier decisions on angle, speed
and spin. If it is a go, there are no more warmups, and the final backswing begins.
The "pause" happens as we come to the end of the natural backward motion
of the cue, so we can make a smooth transition to the forward swing. All strokes
start from zero, and accelerate to whatever speed you're hitting the shot with.
The "finish" is exactly how you described it. The grip hand ends up
in the armpit area, close to the chest; and the tip is on or close to the cloth,
some distance past where the CB was sitting. The "freeze" is an opportunity
for self-evaluation, that happens after the stroke is over, and you have remained
motionless, except for your forearm. The freeze allows you to check components
of your stroke, including the grip finish, tip finish, and speed control.
When do muscle transitions occur during the stroke?
from Spiderman:
if
the real reason for a "pause" is to allow the "backswing"
muscles to stop working before the "forward swing" muscles take over,
then there is absolutely no need for a pause in MOTION, only a pause in acceleration.
When the "backswing" muscles relax, the stick is still moving backwards. There can be a finite period of relaxation before the "forward swing" muscles contract and apply force. AT THIS POINT, AND FOR A FINITE TIME AFTERWARD, THE STICK IS STILL MOVING BACKWARDS. It takes some finite time for the "forward swing" muscles to accelerate the stick to zero velocity. There will then be no finite time at zero velocity because the acceleration is continuous, so the stick progresses smoothly (semi-sinusoidally) from backward to forward velocity.
For this example, the "pause" was in acceleration, not velocity. This relaxation of backswing muscles and subsequent resumption of opposite force occurred entirely before the backwards motion ended.
What is the definition of "pause"?
Strictly, the word "pause" does imply stopping for more than an "instant." When a player has an obvious "pause" between the end of their back-swing and the beginning of their forward-swing, I like to refer to it as a "deliberate pause" or a "distinct pause." Here, the implication is clear: the cue is held stationary (stopped) for more than an instant.
Strictly speaking, if the cue stops only for an "instant," there is no "pause." An "instant" does not involve any passage of time. A "pause" does imply a "stop" (zero speed) for a distinct amount of time. For example, when a free-swinging pendulum changes direction at is highest point, it does "stop" for an "instant," but it does not "pause." The speed gradually and smoothly changes from negative (in the backward direction) to positive (in the forward direction), through zero. The speed does not stay at zero for any amount of time. At the tiniest fraction of a second before the speed is zero, the pendulum is moving slowly in one direction (negative speed); and at the tiniest fraction of a second after the speed is zero, the pendulum is moving slowly in the other direction (positive speed). The speed is zero only for an "instant." Not even the smallest fraction of time passes during that instant.
Now, having said all of that, I don't think it really matters that much. People will interpret the word "pause" in different ways; but as long as you are clear and consistent and people know what you mean, nothing else really matters. Again, I like to use the phrase "deliberate pause" when there is a distinct "pause" in the action (i.e., the stop occurs for more than just an "instant"). For example, both Allison Fisher and Buddy Hall (and others) obviously have a "deliberate pause" before their final forward stroke. I think the phrase "pause for only an instant" is also OK when there is no "deliberate pause"; although, it is strictly not proper. When somebody rushes or jerks the transition between back and forward motion, there still is a "stop for an instant" (because the cue still changes direction and has zero speed for an instant). I would call this a "pauseless and rushed" transition.
Why should I "pause"?
See item 4 in the stroke "best practices" document.
Stretch wrote:
Because
when there is a mechanical error in the stroke it usually happens in the transition
from back stroke to forward stroke. Simply put, the end of your backstroke is
the start of your forward stroke. So if the backstroke does not come back right,
the forward stroke is adversely affected. A slow drawback, and slight pause eliminates
this problem. Also the pause is when you re-focus on the ob's contact point. Yes
"re-focus". During the practice strokes your eyes are scanning back
and forth. When you are ready a back stroke and transition can for a split second
distract your focus, even if you don't take your eye off the ball! A slight pause
allows you to re-focus, or burn with intensity that vital little bit. It makes
one simply react to the target from the trigger position without the distraction
of having any moving parts going on at the same time.
Rod wrote:
Players
with less experience get in a hurry to shoot a shot. Doing so they snatch the
cue back. I have a phrase I like to use. "Finish Your Backswing".
"Gradually" bring the cue tip to the C/B and pause, let your focus go from tip placement to the O/B during this pause, "Gradually" start the cue back, (this is important because a snatch will make your backswing short) slight pause, then slowly start forward, no matter the power needed. This is the transition area. If you start forward fast, you just wasted the preparation needed to make a smooth stroke.
What you'll find, once you learn to slow down your stroke, you'll
hit the cueball exactly where intended. The reason pool players never excel is
they don't grasp the importance of these fundamental movements. You have to be
accurate and quick movements will surely make you loose your focus.
What is a slip stroke and why is it used?
Bob_Jewett wrote:
Here is an article from
Billiards Digest that describes several kinds of stroke including the slip stroke:
http://www.sfbilliards.com/articles/2005-10.pdf
And here is one that describes some other strokes: http://www.sfbilliards.com/articles/2005-11.pdf