Back arm perpendicular- why?

[crosseyedjoe]

But I am. You get the highest cue ball speed with the fastest stick speed. The acceleration at the instant of impact in not significant. This has been discussed extensively before, and you may want to look over Dr. Dave's recent articles on this for the details.

1. and how do you reach faster velocity when distance is constant?
2. what do you mean by cue stick peak velocity after peak acceleration? are you saying that you can can go faster when the acceleration is now being affected by the retarding force of your muscle?

 

[softshot]

We know peak acceleration occurs at the middle of the stroke...

we know that a level cue at the cueball delivers the most accurate impact.

if we force the middle of the stroke to occur at the cueball with a level cue.... (the Set position)

as long as your grip or your shoulder do not alter the path of the cue..

your grip position at impact should be perpendicular.. the middle of the stroke..

peak acceleration plus peak accuracy... equals the right way to do it..

JMO

 

[softshot]

But I am. You get the highest cue ball speed with the fastest stick speed. The acceleration at the instant of impact in not significant. This has been discussed extensively before, and you may want to look over Dr. Dave's recent articles on this for the details.

you will probably blow me out of the water with a bunch of math here but...

given these two choices..

would you rather be on the motorcycle that accelerated to 55 MPH before impact with the wall.???

or the driver of the bike that just barely slowed down to 55 MPH at impact with the wall????

acceleration matters... and acceleration imparts momentum which imparts a consistent force that is unrelated to speed..

human muscles can control acceleration much better that they can control velocity.. from what I have read..

 

[Fatboy]

Here's my dilemma:

I've been told by players much more accomplished than I that I should work on getting my back arm perpendicular at contact. Nearly every book, article, AZB post, etc. that discusses fundamentals seems to agree.

When I play, my arm is usually forward of perpendicular at contact. I wouldn't say dramatically, but very clearly visible to anyone who's looking. I've done this for years, because it's more comfortable, it feels more natural to me, and I seem to get significantly more consistent results.

I've tried several times to "fix" my stroke, by moving my grip hand back, or addressing the ball differently- for months at a time, even - with no appreciable result other than feeling awkward at the table, and playing significantly worse than I know I'm capable. I feel like I have enough "stroke" playing my usual way, to do anything I need to do at the table, but I can't help but wonder if there's a compelling reason to try fixing my mechanics again.

Ultimately, I don't want my game to be limited by something like this, so I thought I'd put the question to the board. What are the benefits, scientific or otherwise, of addressing the cue ball with your back arm perpendicular to the ground?

Thanks!

it took me way too long to get that perpendicular spot at the point of contact, I did and by the time I got it I was a better player-perhaps because it took so long, years later I have watched a zillion players and came to one conclusion-its over rated, Lassiter was WAY choked up on his cue, Davenport was perhaps the closest to 90 degrees as anyone, and I have seen less champions that are open more than 90 degrees,

having said all that, I think its better to be 90 or under, open greater than 90 degree strokes look funny and limited in some ways.

 

[Patrick Johnson]

Bob Jewett:
The acceleration at the instant of impact in not significant.

softshot:
you will probably blow me out of the water with a bunch of math here but...

given these two choices..

would you rather be on the motorcycle that accelerated to 55 MPH before impact with the wall.???

or the driver of the bike that just barely slowed down to 55 MPH at impact with the wall????

No math necessary. Since they're both going the same speed at impact, the effect of the collision is exactly the same. Whether they get to that speed by speeding up or slowing down (or coasting) is irrelevant.

acceleration matters... and acceleration imparts momentum which imparts a consistent force that is unrelated to speed...

Acceleration doesn't "impart momentum" that's unrelated to speed, and it doesn't matter to the amount of force at a given speed.

human muscles can control acceleration much better that they can control velocity.. from what I have read...

I don't know what that means.

pj
chgo

 

[Patrick Johnson]

peak acceleration plus peak accuracy... equals the right way to do it..

I think this should be "peak velocity plus peak accuracy".

Think of driving a car. As long as your foot is pressing the accelerator (gas pedal), the car is accelerating*. You can back off on the gas a little so you're accelerating less, but still accelerating some and still gaining speed (velocity). So peak acceleration can occur before peak velocity - but peak velocity is where you get the most consistency.

pj
chgo

*P.S. Technically, "acceleration" means any time your speed is changing, either speeding up or slowing down. Taking your foot off the gas, or even hitting the brakes, is "accelerating" in technical terms. But for this discussion I think that just confuses things, so I'm using the word "accelerate" the way non-technical people use it: to mean speeding up only.

 

[Cornerman]

We know peak acceleration occurs at the middle of the stroke...

we know that a level cue at the cueball delivers the most accurate impact.

if we force the middle of the stroke to occur at the cueball with a level cue.... (the Set position)

as long as your grip or your shoulder do not alter the path of the cue..

your grip position at impact should be perpendicular.. the middle of the stroke..

peak acceleration plus peak accuracy... equals the right way to do it..

JMO

Ummm.... No.

I think you're confusing acceleration with velocity.

I think peak acceleration (linear acceleration, horizontal to the cueball) is when the hand is about 45 degrees short of perpendicular (wrt horizontal). Peak velocity is when the hand is at perpendicular.

The velocity just before and just after perpendicular is almost the same. So, hitting around perpendicualar is "right" from a constant/consistency point of view. A few degrees from perpendicular still gets you about the same speed. And at perpendicular, you should be at about zero acceleration as others have said.

A good case can be made that says that many (most?) top players are actually decelerating their cues just prior to impact with the cueball. That's okay since it's the velocity that matters, not the acceleration (which is nearly zero at impact anyway).

Fred

 

[Cornerman]

would you rather be on the motorcycle that accelerated to 55 MPH before impact with the wall.???

or the driver of the bike that just barely slowed down to 55 MPH at impact with the wall????

Same impact.

acceleration matters... and acceleration imparts momentum which imparts a consistent force that is unrelated to speed..

Acceleration doesn't impart momentum. Speed does.

human muscles can control acceleration much better that they can control velocity.. from what I have read..

Why would you think that? Even if this was true, what exactly would it matter? Acceleration at impact doesn't mean anything. Velocity does.

Look, if you are standing on a table, you're accelerating towards the earth at gravitational acceleration, even if you're actually not moving. If the table is only 4 feet high, and you jump off, you're not accelerating any more than gravitational acceleration, but your velocity starts to increase. You'll land on the floor with no problem, because you haven't accelerated to any significant speed.

Take the same situation but jump off a 40' building. Do you understand that you'll be accelerating the same regardless of how high you started (terminal velocity and wind resistance dismissed, of course)? But, when you hit the ground, you will have accelerated to a tremendously significant speed. And you'll get pancaked. So, the fact that all three cases the acceleration is exactly the same means nothing. The velocity at impact does.

I hope that sheds more light into the terminologies.

Fred

 

[Bob Jewett]

1. and how do you reach faster velocity when distance is constant?
2. what do you mean by cue stick peak velocity after peak acceleration? are you saying that you can can go faster when the acceleration is now being affected by the retarding force of your muscle?

If the distance over which you are accelerating is constant, and assuming your arm can provide uniform maximum force over that distance, but cannot go instantaneously from no force to maximum force, then the technique to get to maximum stick speed at impact would be to backstroke as quickly as possible, don't have any pause at the end of the back stroke, and have the full maximum force applied from somewhat before the backstroke stops until contact with the cue ball. But I don't think arms work that way, and I don't think that would be a good technique for any shot but a power break.

As for question 2, a definition may help: Acceleration is by definition the rate of change of velocity. If there is (positive) acceleration, the velocity is increasing. If the stick is still accelerating, and you wait a little while, the stick will be going faster, by the definition of acceleration. Also by the definition of acceleration, peak velocity is achieved exactly when the acceleration is zero.

 

[crosseyedjoe]

As for question 2, a definition may help: Acceleration is by definition the rate of change of velocity. If there is (positive) acceleration, the velocity is increasing. If the stick is still accelerating, and you wait a little while, the stick will be going faster, by the definition of acceleration. Also by the definition of acceleration, peak velocity is achieved exactly when the acceleration is zero.

True, only if there in no retarding force associated along the plane of action.

As for question 2, a definition may help: Acceleration is by definition the rate of change of velocity. If there is (positive) acceleration, the velocity is increasing. If the stick is still accelerating, and you wait a little while, the stick will be going faster, by the definition of acceleration. Also by the definition of acceleration, peak velocity is achieved exactly when the acceleration is zero.

What mechanical system is this?

 

[Bob Jewett]

... What mechanical system is this?

My statement was based simply on the definitions of acceleration and velocity. Those definitions apply to all mechanical systems. I looked briefly for some tutorials on the web, and you can find several using the words "velocity acceleration definition" with various levels of technical detail. Here is one with some helpful diagrams:
http://hep.physics.indiana.edu/~rickv/More_Kinematics.html

 

[alstl]

Yes, if you can make your arm a free swinging pendulum. It's not. You are using muscle contraction to mimic the pendulum movement.

Exactly.

..........

 

[Patrick Johnson]

...if you are standing on a table, you're accelerating towards the earth at gravitational acceleration, even if you're actually not moving.

A nit: acceleration means a change in velocity (which wouldn't happen until you step off the table), but I agree with everything else.

pj
chgo

 

[Cornerman]

A nit: acceleration means a change in velocity (which wouldn't happen until you step off the table), but I agree with everything else.

pj
chgo

Well.... your body still must have an acceleration vector towards the earth or else you'd have no weight force. The table just happens to be opposing it.


Fred

 

[Bob Jewett]

Well.... your body still must have an acceleration vector towards the earth or else you'd have no weight force. The table just happens to be opposing it.


Fred

If you base acceleration on net force, which is usually done, then the opposing forces cancel and you have zero net acceleration.

 

[Cornerman]

If you base acceleration on net force, which is usually done, then the opposing forces cancel and you have zero net acceleration.

Well of course. But you'd have a hell of a time trying to calculate that opposing force if you denied yourself the use of an acceleration term. If you do deny yourself this, please don't design any bridges for me.

The gist of my post was that the word acceleration wasn't what defined the impact that's being discussed. Summing up individual forces is okay given this context.

Fred

 

[Patrick Johnson]

A nit: acceleration means a change in velocity (which wouldn't happen until you step off the table), but I agree with everything else.

Well.... your body still must have an acceleration vector towards the earth or else you'd have no weight force. The table just happens to be opposing it.

Oh, I see what you're saying. I'll defer to you and Bob on vectors.

pj
chgo

 

[crosseyedjoe]

I think this should be "peak velocity plus peak accuracy".

Think of driving a car. As long as your foot is pressing the accelerator (gas pedal), the car is accelerating*. You can back off on the gas a little so you're accelerating less, but still accelerating some and still gaining speed (velocity). So peak acceleration can occur before peak velocity - but peak velocity is where you get the most consistency.

pj
chgo

"peak velocity plus peak accuracy" - no argument on that one.

As for the car;
1. It's possible because it involves a wheel system.
2. Letting off on the gas a little is not a retarding force.

 

[crosseyedjoe]

My statement was based simply on the definitions of acceleration and velocity. Those definitions apply to all mechanical systems. I looked briefly for some tutorials on the web, and you can find several using the words "velocity acceleration definition" with various levels of technical detail. Here is one with some helpful diagrams:
http://hep.physics.indiana.edu/~rickv/More_Kinematics.html

This one does not apply to all mechanical system: "Also by the definition of acceleration, peak velocity is achieved exactly when the acceleration is zero."

What you are suggesting mostly concerns classical pendulum mechanical system in which the acceleration acts vertically and the acceleration goes to zero once the pendulum reaches the bottom(at peak velocity) because its direction is now tangent to the direction of the acceleration.

Stroke is not a pendulum system.

 

[crosseyedjoe]

A nit: acceleration means a change in velocity (which wouldn't happen until you step off the table), but I agree with everything else.

pj
chgo

PJ, remember the third law of motion, opposite and equal reaction. You always have an acceleration component even when standing still. It's just that the forces are cancelling out which shouldn't be confused with acceleration cancelling out. That's why you will weigh less on the surface of the moon.