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Thursday, December 16, 2010

Understanding the Angles in the "New Ball Flight Laws"

(UPDATE: At the end of this post, I've added a copy of TrackMan's diagram showing the angles involved in this discussion.)

If you're like Court (and me, when I first started looking at this), you think these "new ball flight laws" are just crazy. I certainly understand. As I said in the comments on yesterday's post, one of the reasons I waited to do these posts was because it was hard to get my mind around them. They seem contradictory.

The breakthrough for me was realizing that the original concepts we were taught are a mixture of these so-called "new rules" and some things that, if you stop and think about them, don't make sense anyway. Today I want to try and show you what you already know that conforms to these "new rules." I think you'll be surprised how much sense they actually make. I'm going to use Court's comments as a jumping-off point -- for the simple reason that originally I would have given the same sort of objections, but Court states them more clearly.

The big point of contention is that, according to the "new rules" the ball doesn't come straight off the face in the direction of the club path; rather, it shoots off in roughly the direction the club face is pointed. Court raised a valid objection when he commented:
The same physics apply to bowling when you see a pro throw a ball that goes out straight and breaks late. You also see it with baseball pitchers who can make the ball break closer to the plate.
I would have given similar examples, and he's completely right. This is something we observe every day of our lives. It really is "simple physics," as he repeatedly put it.

Unfortunately -- and this is why it took me so long to catch on -- it's the wrong simple physics. The laws that regulate how a ball behaves when it is being held and directly launched in a given direction with a given amount of spin are slightly different from a ball that is not being held, but being hit and receiving its direction and spin through that contact. It's the difference in control that the pitcher has versus the control the batter has. The batter has to deal with laws of physics that don't affect the pitcher.

Specifically, the batter has to deal with this law: The angle of incidence equals the angle of reflection. Here's a visual explanation from

Angle of incidence diagram

Simply put, when a ball bounces off a surface at an angle -- the way a golf ball does when the face is open or closed relative to the swing path -- it doesn't bounce back on the original line. If the surface with the point of contact in our diagram was the club face and the line representing the angle of incidence was the ball's contact along the swing path (the actual swing path would be coming from the lower right of the diagram, along the same line of incidence), the traditional way of shotmaking says that the ball would contact the club face and then travel directly back along that line. (There are golf-specific diagrams later. If that wasn't quite clear, just hang with me.)

The traditional "rule" doesn't make sense when it's put that way, does it? Ironically, Court agreed with the new rule unintentionally:
Again - it's basic physics that work when you can hit the ball hard enough with enough spin that the fade or draw spin can't take over until the ball loses enough velocity for the air pressure to affect the ball. Most of us can't do it because we don't hit the ball hard enough.
If we can't hit the ball hard enough to delay the effect of the spin... doesn't that mean the ball should head off-line immediately for most players? I would agree with him entirely -- it's the most sensible application of the traditional rules -- but that logic agrees with the new rules! Court instinctively realizes that the new rule is correct, yet believes that the old rule makes more sense... probably because he was taught that way by teachers he respects (who were taught by teachers they respected, etc.). And I would be the first to say that's a good reason to be skeptical of any so-called "new rules." But when even the logic of the traditional way seems to agree with the new rules, perhaps it's time to reconsider. (Tomorrow I'll look at some classic teaching that seems to back up this new understanding.)

According to Dave Pelz (and the other "new rules" guys), the face angle is apparently responsible for 5/6 of that total angle between the incidence and reflection lines in the diagram. The remaining 1/6 is determined by the swing path, so it looks like the speed of the club does have an effect... but not as much as we thought. Even the big hitters have to deal with this "angle of reflection" stuff.

I can think of two ways that you already use this knowledge in your swing. One I mentioned in yesterday's comments -- shanks. When you hit a hosel rocket, the ball doesn't start straight toward the target, then curve away; it shoots straight off to the side. This is what the new rules predict. The only way the hosel rocket goes toward the target is if you hit it square on the front of the hosel. And you expect this -- that's why you're so embarrassed. ;-)

Hitting down with an iron diagramA less obvious example involves hitting down on iron shots. Take the diagram at left. The club face is coming down at an angle from the upper right, which means (in effect) that the ball is coming up from the bottom left. Where the ball contacts the club face, it rolls up the face -- giving it backspin -- and causing it to go up, as the arrow pointing from the club face to the upper left corner shows. "Hit down to go up" is classic teaching about iron play. None of us really expect to drive the ball down into the ground, do we? In fact, if we don't pinch the ball against the ground -- a real possibility if the ball is in thick rough -- the ball will actually fly even higher!

Hitting a push-draw diagramSo I take that same diagram, flip it upside-down and gray it out, then draw over it to diagram a right-hander's push-draw. Now instead of hitting down to make backspin, we're hitting from the side to create sidespin. Now tell me... does it make sense that the club face, which is closed and coming from the lower right corner of our diagram, is going to start the ball toward the upper left corner, along the swing path? Logically, the ball should head toward the lower left corner as the ball "reflects" off the face and gathers sidespin. It's going to head to the lower left and curve even farther left!

It's the exact same physics, just viewed from a different angle. But while the downward hit with the iron is traditional teaching, the hit from the side isn't. Yet in both cases the ball receives its direction and spin by being hit. Since the traditional model predicts the first example, it should also predict the second example because the physics are the same... but it doesn't. And that means the traditional model of the second example is wrong.

Or, as the TrackMan folks put it:

TrackMan diagram of ball flight

Do you have a headache yet? Me too... so let's call it for today. Reread this as many times as necessary -- in really small chunks if necessary -- until you can see what's happening. (Look, it took me a few weeks to get a good handle on it. I don't expect you to put it all together overnight.) Tomorrow we'll look at what this really means in terms of how we play golf. Fortunately, the application is much simpler than the theory.


  1. No headache...except from seeing that these laws are wrong for one really simple reason. They start from the wrong place.

    A golf ball does react to, using your term, laws of a held ball. When a golf ball compresses, it is controlled (for the most part) by the contact of a clubface with grooves and angles and texture, and the amount of compression and expansion of the ball - plus the grooves, of course.

    Your diagrams should be the first clue that these new "laws" are incorrect explanations of what is going on. The ball isn't deflecting - the ball is sitting still.

    You're starting from the wrong point.

  2. "Every action has an equal and opposite reaction."

    This is basic physics. When two objects are involved, each exerts force on the other. When the club exerts force on the ball, the ball exerts an equal and opposite force on the club. Whether the ball is moving or not doesn't matter -- the forces are the same.

    I understand your reluctance, Court. Fortunately, there's a simple way for you to test this. Simply go to the driving range -- or your backyard, if you have room -- and duplicate the setup in the last picture. Close the face of your club and make an inside-out swing at the ball. See if the ball actually travels out in the direction you're swinging the club.

    In fact, make it even simpler. Set up so you can make a straight swing toward your target, but close the club 30° or so relative to your aim line... then hit the ball. See if it flies straight for a while then curves, or shoots off at an angle to your aim line. If you can hit the shot you expect, make a video of it and send it to me. I'll be more than happy to post it.

    But bear in mind that what I said in this post is what the TrackMan people say they actually measure. (I added their diagram to the post above, so you can see it.) If you're saying that TrackMan is incapable of measuring these things, you're gonna have to prove that the major scientific measuring tool used in golf flight research is unreliable. I'll be real interested to see you do that. ;-)

  3. Now you're back to talking about putting again - and putting is along the ground, which takes spin out of the equation almost immediately after the strike, and adds friction of ground contact.

    The physics of flight and the physics of roll aren't the same.

    Telling people that if you move your club along a line with the face open or closed, the ball isn't going to roll towards the hole doesn't require a physics demonstration or any kind of drawing. (and if you really want to mess with someone's head, show them Billy Mayfair's old putting stroke with the big loop) :-D

    Here's what I see with your first three diagrams. Two of them show the ball in motion at impact - which we know is incorrect - so they have to go. The third one is basically correct except that it shows a ricochet motion instead of what happens on a golf shot - which is the ball compressing against the club face and climbing the clubface, which is where we get the spin. The more spin, the higher the ball will climb - less spin gives us the lower trajectory.

    The bottom diagram is simple geometry - but at least the ball isn't moving before impact.

  4. I'm not going to debate you on this any more, Court. Usually you make me think, but now you're not even listening to what I said. As a simple example, I never mentioned putting in my last comment; in fact, I specifically mentioned "flight." You've just decided this is wrong and you're going to argue until you're blue in the face.

    So be it. I've just posted a slo-mo video showing actual ball contact with various irons... and lines showing the swing path, face angle, and resulting ball path. This is visual evidence of what TrackMan documents. If you don't want to believe it, that's your right... but don't blame me if you keep hitting trees when you mean to hit around them.

  5. That's not a putter in the bottom diagram ?

    And if I want to get blue in the face, I'll just go stand outside for 10 minutes. :-D

  6. Nope, it's not a putter. I didn't have a lot of time to make that last diagram (the one with the iron was one I made some time back), so I just sketched in a block to show the position of the club face. Even if I had rounded out the back, I think it would have looked like a mallet putter.

    It must be warm down there in Atlanta. It wouldn't take 10 minutes to turn blue up here. ;-)

  7. Whoah! I was interested in discussion on this subject but it appears to have turned into a Galileo "Earth revolves around the Sun"-type heresy for some people. I've struggled with these 'laws' (ball flight not astrophysics) but the evidence was out there I just couldn't interpret the information. 8" diameter tree on target line, body aligned left of tree, clubface aligned at target, bingo - I hit skinny tree.

    I always believed it was my poor golf that was the source of the problem but in fact the problem was using 'golf physics' instead of mechanical physics.

    It is always interesting how people react when you challenge long-held beliefs and provide them with both proof and evidence. At first I didn't want to believe what I was seeing either thinking that as an amateur golfer what do I know? But as with everything only with knowledge comes true understanding.

    My parting shot is you call tell how correct a person's argument is by the number of people telling them they're wrong.

  8. Jonny, anytime you challenge long-standing beliefs in anything, people are going to be uncomfortable. Like I said, it took me quite a while to get my head around these "new rules," and it's going to take readers a while as well.

    Plus, anything can make it more difficult... like Court mistaking my final drawing as a putter when I didn't mean it to be so. It does look the way I generally draw putters in diagrams, and I didn't realize it when I drew it. That may have had as much to do with the confusion as anything.

    I think most of us instinctively know there's something wrong here, but we can't put our fingers on it. That makes it hard to trust new information -- if you aren't sure exactly what's wrong to begin with, how can you be sure this odd-sounding new approach is any better?

    That's what's nice about a blog. You can get feedback and try to answer it -- I would never have thought about how that last picture looked otherwise -- plus you can leave it all up so people can take their time and mull over it until it make sense.