How Club Path and Face Angle Determines Ball Flight

[Ringer]

Ok.. one last attempt.

Instead of thinking the club is in motion, imagine that it is stationary. Lets move the ball instead on a directly line straight at the middle of the clubface, but angle the clubface with a loft of 20 degrees and angled 5 degrees open.

When the ball hits the clubface, what direction do you think the ball will go?

Same in pool. When you bounce the ball off the rail at an angle, where does the ball go even though the rail is cussioning some of the impact?

[laconic517]

Ok.. one last attempt.

It doesnt work that way at all though. Youd never be able to shape the ball at all, the whole idea of the golf swing would go out the window. If what you say is correct how do you expect to shape the ball at all? If the club face is open or closed it will go straight right or left which obviously doesnt happen unless its an extremely open or closed face such as a duck hook or banana slice.

[greenail]

Ok, I think this is bullet proof,

Referencing this page for the diagram http://www.brainycreatures.org/physics/collision.asp



If you look at the angle of the deflection it is 90 degrees not accounting for friction and cannot be less than 90 degrees unless the club face is spinning or the ball is spinning on the ground. We all know that the club face is spinning to some extent depending on your swing, but that gear action is almost always going to be in one direction, and if it had enough of an impact you'd never see the opposite spin (hook spin).

Now if we accept that the deflection is not acute, then we need to look at how much the club path vs the open/closed face has an impact, and I think you can see that if the club is square it will only go on a tangent line. As you open the club face more and more the ball moves off target more and more.

The problem with the argument.

Which has more impact on the initial direction of the ball, face or path?

Well if your path is 20 degrees open to the target line and the face is square then the path has more influence on the initial direction.

If your path is on tangent with the target line and your club face is 20 degrees open the club face is the culprit.

If your path is 20 degrees open and your face is 20 degrees open they both will combine for a spectacular banana slice into some poor schmo's house.

So what is the right answer?

[Ringer]

It doesnt work that way at all though. Youd never be able to shape the ball at all, the whole idea of the golf swing would go out the window. If what you say is correct how do you expect to shape the ball at all? If the club face is open or closed it will go straight right or left which obviously doesnt happen unless its an extremely open or closed face such as a duck hook or banana slice.

You can still shape the ball... but certain things you THINK cause the ball to move aren't as accurate as you thought and often lead to over-corrections.

For example: Common thought is that a pull hook is where the clubface is closed to the target and the clubhead is traveling on an outside in path. In reality the path is actually square to the target* or even a little inside out, but the clubface is closed. So the result is that someone swings even MORE inside out thinking they need to swing further right. All that does is cause the ball to have MORE spin and go even FURTHER left. *Square here meaning on a perfect tangent toward the target from the arc of the swing where contact is made.

[Big Lex]

More great posts on this topic...

Anyway, as promised, the things I've read.

Cochran and Stobbs "The Search for the Perfect Swing" is a 40 year old volume, but has considerably detailed data collection, with high speed cameras, etc. Data collection is clearly much more sophisticated today, but the physics haven't changed, and the book is very well researched and written, so you have to be very careful about simply discarding what they say. However, the book isn't referenced like a textbook, so you can't independently verify anything they say. For what it's worth, on page 124:

"Which is more important in determining the direction the ball starts off on: the direction in which the clubface is pointing, or the direction of clubhead travel? A ball will always leave a clubface somewhere between these directions; but usually nearer the direction along which the clubface is pointing than tha along which it is being swung. In the case illustrated, the angle between these two is 20*, and in a full shot an average golf ball would go off at perhaps 7* to the right of the perpendicular to the clubface. (If the face of the club were perfectly smooth it would leave exactly at right angles to the clubface; in a putt the angle would be 4* or 5*."

The second book I mentioned, The Physics of Golf, by Theodore Jorgensen, also describes the ballistics of impact and initial ball flight. The discussion is a comprehensive prediction/modeling of the event, based on known laws of physics and certain estimations of friction, elasticity, etc. He doesn't specifically address the question in this post, but his scale diagrams clearly indicate that he predicts the initial flight would be closer to the face angle than the club head path. The discussion is on pages 123-131 in the technical appendix. He mentions that determining the precise conditions of impact and initial flight are extremely difficult to both predict and measure, and that many factors, including such things as the mass distribution of the ball, would affect the results. Also, any predictions and determinations are generally based on the hypothetical perfect, sweet spot hit, in which there is absolutely zero roll of the clubface on impact.

As a last part of my contribution to the thread, I am doing some additional research on launch monitors...it may be a while before I have anything to say.

From reading what we have so far, it's agreed that both factors influence the starting direction of the ball. It's unclear which has a greater effect, and by how much. It's also been suggested that the relative contribution of each factor may vary depending on exactly how much the face and path differ, the loft of the club in question, the velocity of the club, etc.

Can we get any geekier?

[Big Lex]

Just an aside...greenail, where did you get that lovely golf-themed photo used in your posts?

[greenail]

google image search.

[Ringer]

More great posts on this topic...

Good post. Thank you for all of that research I know you had to do...not to mention the typing.

[iacas]

I'm back, which I suppose makes me a liar since I said I was done. So be it... I'm a bit of a geek and I find this discussion interesting. But hey, I'm going to avoid talking about expensive launch monitors this time.

Thanks JP and Ringer for their thoughts... I have some quick questions.

If you look at the angle of the deflection it is 90 degrees not accounting for friction

Perhaps I'm misunderstanding what you're saying, but we can't "not account for friction." It's the "sticking to the clubface" that accounts for the ball being "dragged" in the direction of the club's path.

If there were no friction, agreed, the ball would have to rebound perpendicular to the clubface. That's (literally) Physics 101. So unless I've misunderstood your post, I don't quite get what you're saying. A golf ball being hit by a driver is not a frictionless setup.

You can still shape the ball... but certain things you THINK cause the ball to move aren't as accurate as you thought and often lead to over-corrections.

My initial reaction to what you wrote was the same as the guy who said "Youd never be able to shape the ball at all." And please, let's not get into pool. I can make a pool ball do a lot of things off the rail - go left, right, etc. Even without sidespin a pool ball rarely reflects back at the same angle as the incident angle. Add in topspin ("follow" or "roll") or backspin (which in pool is "draw" spin) and things get even more freaky. Please, let's not use pool balls off rails as an example: I don't think it's an analogous system.

In reality the path is actually square to the target* or even a little inside out, but the clubface is closed.

I don't know if this qualifies as a tautological argument, Steve, but you can't just say "in reality" and expect us to accept it as fact.

If a true pull-hook was actually caused the way you've described, I'd be wrong and you'd be right: it's more about club face angle. But that's the very topic we're discussing... you see?

From reading what we have so far, it's agreed that both factors influence the starting direction of the ball. It's unclear which has a greater effect, and by how much. It's also been suggested that the relative contribution of each factor may vary depending on exactly how much the face and path differ, the loft of the club in question, the velocity of the club, etc.

Very much in agreement with that. We're really arguing/discussing some pretty nitty gritty stuff. We're basically sweating over 20% or so - whether it's 60/40 or 40/60. And it's not even a constant: under one set of conditions it may be 70/30 and under another 55/45.

Can we get any geekier?

Sure! How many chapters do the two recently published golf/physics books have. We could start 10 threads per chapter of The Golfing Machine alone.

[Ringer]

Perhaps I'm misunderstanding what you're saying, but we can't "not account for friction." It's the "sticking to the clubface" that accounts for the ball being "dragged" in the direction of the club's path.

Friction will not cause a ball to travel parallel to the direction of the moving body at oblique angles. What is instead does is cause the spin.

Think about this. Take a beach ball and toss it up in the air. Karate chop it on one side. Now, the friction of your hand to the plastic will make it spin, but the direction will be at an off angle to where your hand hit it relative to the center of the beach ball. It won't be EXACTLY 90 degress but it will be more in that direction than the direction your hand traveled...and I can guarantee there is WAY more friction between your hand and the beach ball than there is between the golf ball and face. The further off to the side of the beach ball you hit it, the more at an off angle it will go AND the more spin it will have.

My initial reaction to what you wrote was the same as the guy who said "Youd never be able to shape the ball at all." And please, let's not get into pool. I can make a pool ball do a lot of things off the rail - go left, right, etc. Even without sidespin a pool ball rarely reflects back at the same angle as the incident angle. Add in topspin ("follow" or "roll") or backspin (which in pool is "draw" spin) and things get even more freaky. Please, let's not use pool balls off rails as an example: I don't think it's an analogous system.

Just because it doesn't match the EXACT conditions of golf impact doesn't make it a useless tool for understanding. If you keep limiting the examples to what you only wish to see then you have pretty much matched the definition of "narrow minded". Think about it, if i kept tossing out every explination you gave and repeated over and over my mantra, you'd claim me to be narrow minded.

I don't know if this qualifies as a tautological argument, Steve, but you can't just say "in reality" and expect us to accept it as fact. If a true pull-hook was actually caused the way you've described, I'd be wrong and you'd be right: it's more about club face angle. But that's the very topic we're discussing... you see?

It wasn't meant to be an argumentative statement but rather an example of how people mis-diagnose.

Very much in agreement with that. We're really arguing/discussing some pretty nitty gritty stuff. We're basically sweating over 20% or so - whether it's 60/40 or 40/60. And it's not even a constant: under one set of conditions it may be 70/30 and under another 55/45.

The variables have been accounted for but there is a reason the club manufacturers do not release much information about this. The PGA manual still says that path is the determining factor. They would basically be going up against decades of teaching and ruin more than the PGA's share of instructors brains. It would be as if I had proof that recycling was more harmful to the earth than not recycling. People would get angry and near violent. Plus all the people that would have their jobs in jeaopardy. You would bet all the numbers and data would be hidden from the public as best as possible.

[iacas]

Friction will not cause a ball to travel parallel to the direction of the moving body at oblique angles. What is instead does is cause the spin.

That wasn't your comment, Steve, but I'll respond anyway:

a) I never said it would travel parallel. Let's avoid the straw men and putting words in people's mouths. b) It results in spin AND affects the ball's initial direction. Even Dave Pelz notes that path has some (minimal) impact on putts, and the ball doesn't "stick" to the clubface nearly as long on putts as it does with a driver.

Take a beach ball and toss it up in the air. Karate chop it on one side. Now, the friction of your hand to the plastic will make it spin, but the direction will be at an off angle to where your hand hit it relative to the center of the beach ball. It won't be EXACTLY 90 degress but it will be more in that direction than the direction your hand traveled...and I can guarantee there is WAY more friction between your hand and the beach ball than there is between the golf ball and face.

I borrowed my kid's beach ball. It's inflated a decent amount, though it's not super-inflated.

I tossed the ball in the air. As it was coming down, I slid my hand horizontally (a horizontal karate chop) across the bottom of the ball. The ball traveled about 15 degrees above horizontal in the direction my hand moved and with a little backspin. This was with me nipping the bottom of the beach ball. If I hit the center of the beach ball, it was obviously perfectly horizontal. The closest I could get to 45 degrees was when I hit the ball midway between the equator and pole (45 degrees on the ball, or "southeast" on a compass). Even then, "launch" was about 30 degrees. Obviously that's completely unscientific, and I don't care to make it more so by measuring the size of the beach ball (about two feet in diameter) or the PSI of the air inside it or constructing something that can hit the ball at a precise speed. My simple experience, though, is different than you postulate it would be. Interestingly, I could also change the angle the ball comes off my hand by changing the amount of air inside it. With less air, the ball rebounded closer to horizontal. With an incredibly firm ball (i.e. approaching "frictionless"), the rebound angle moved away from horizontal and more closely to the angle at which my hand struck the ball (and through the center of the ball). Backspin was also reduced with the firmer ball, of course.

If you keep limiting the examples to what you only wish to see then you have pretty much matched the definition of "narrow minded".

Steve, with all due respect, I feel I'm trying to point out the flaws in the examples. That's not quite the same as just randomly throwing out examples simply because the people proposing them disagree with me.

In fact, I'd go so far as to say I believe JP would agree that they're poor examples. Pool balls off rails behave very differently depending on how much spin the ball has (in the vertical AND horizontal axis). It also depends on the speed of the ball (how much the rail compresses), the angle at which the ball hits the rail, the composition of the rail (some rails rebound shorter or longer than others, and rails can firm up over time). The rail also isn't flat nor does it contact the equator of the ball - it's slightly higher than the center of the ball. We can't ignore friction. No "frictionless" worlds work here. I'll gladly agree that without friction a golf ball will rebound perpendicular to the angle of the face. It also won't spin. Again, that's simple physics. And I don't think your beach ball example works either. It certainly doesn't jive with my experiences.

The PGA manual still says that path is the determining factor.

Okay... so isn't that the opposite of what you're saying?

People would get angry and near violent. Plus all the people that would have their jobs in jeaopardy. You would bet all the numbers and data would be hidden from the public as best as possible.

So now it's just a big conspiracy, Steve? I don't understand. Are you saying that:

a) the PGA manual says path is the determining factor b) the PGA knows that to be wrong c) they're not releasing that "it's wrong" information or updating their "manual" because people would get angry and violent?

[greenail]

Pool balls off rails behave very differently depending on how much spin the ball has (in the vertical AND horizontal axis). It also depends on the speed of the ball (how much the rail compresses), the angle at which the ball hits the rail, the composition of the rail (some rails rebound shorter or longer than others, and rails can firm up over time). The rail also isn't flat nor does it contact the equator of the ball - it's slightly higher than the center of the ball.

A Pool ball with spin hitting a rail has different things happening than a golf swing, however a pool ball striking another pool with no spin is a great analogy. I do find it odd that I cannot find anything using friction as a variable in equations describing elastic collisions in 2 dimensions.

[Big Lex]

greenail:

Buy "The Physics of Golf" by Ted Jorgensen. Look in the technical appendix, and he gives you his formulae for determining the starting vector of a golf shot, complete with the allowance/estimation for the coefficient of friction of the club/ball system.

http://www.amazon.com/Physics-Golf-T...7364165&sr;=8-1

And where's the link to your photo?

[Leek]

Anyone interested should try this little test and then report your findings:

do this little test:

Make a chip with a clubface that is 5* closed and a clubpath that is 5* inside/out. If you do it honest and don't fudge the ball is going to START LEFT, not right, but left.

Do the same for 5* open face and 5* outside/in. Ball will start RIGHT.

[iacas]

however a pool ball striking another pool with no spin is a great analogy.

No, it doesn't, and again I think even JP would agree with that. A golf ball being hit by a driver compresses. Pool balls don't (well, they do, but orders of magnitude less than a golf ball).

I do find it odd that I cannot find anything using friction as a variable in equations describing elastic collisions in 2 dimensions.

A golf ball hitting a driver isn't an elastic collision. It's inelastic - energy is lost (in compressing the golf ball).

Pool balls aren't even perfectly elastic, though they're about as close as we really come in "real world" examples. And even then there are plenty of examples when friction plays a role in pool: to be a good pool player you've got to understand how balls behave when they're "frozen" to each other and how "english" (spin) can affect a ball's path. In pool it's called "throw." Here's an example or three: http://www.easypooltutor.com/article251.html http://www.billiardworld.com/frozball.html

[greenail]

Well I've tried my best to digest some of what is written in here:


http://books.google.com/books?id=nHg...r2JtO54xzcJ6FM

It says that there is a curve on which the more open your club face is the more "slip" you will have and the less the effect friction will have on the ball as well as the smaller the "stick" time is. We need to know the coefficient of friction for a modern golf ball to plug into a formula to see what that curve looks like to give us the answer, but i'm afraid the question is more complex than I thought.

BTW i found this by searching on "oblique impact" and friction. Oblique impact is more of what we are discussing, where one object is stationary.