So here's my second blog about ball flight, this one having to do with trajectory control with your iron clubs.  I am far from being any kind of expert on this, but I'll at least tell you what I've learned about producing different trajectories.  One of the things that we all need to eventually learn to do is control the trajectory of our shots into the green.  Most of us just swing and hope the ball goes forward in the air somehow (I have those days too).  But if you really put some thought into your trajectory, you can play more effective golf.  I will say again, that my methods here might not work for everybody.  Everyone has their own take on doing things, and this is just my own strategy for hitting high and low shots.  It has proven effective for me, though, so maybe it will work for you too!
 
If you are a beginning golfer, or one who struggles with inconsistent contact most of the time (you hit shots fat or thin much of the time), this blog will probably be detrimental to your game, so don't read it, or if you do, don't think about it.  This is a lot of information that won't necessarily help you hit the ball more solidly, and if you have all of these new thoughts in your head while you're still just trying to learn the swing, you're going to melt down!  Just work on consistently hitting the ball and then come back when you feel the need to adjust your trajectory.  However, if you're a pretty good ballstriker and want to hit it higher or lower, read on.
 
A caveat first:  Modern clubmaking technology has greatly affected ball launch characteristics.  Many game-improvement iron sets (like Adams Idea, Nike Slingshot, Titleist AP1, Callaway Big Bertha, and others like them) are designed to hit the ball higher, even with less loft.  This is due to the lower center of gravity in these clubs, which in effect helps the club get "under" the ball and lift it high in the air.  This low center of gravity is paired with lower lofts on each club, so you get more distance with a higher trajectory.  That's why you might see a 45 degree pitching wedge in many game improvement sets, while a traditional forged pitching wedge has about 48 degrees of loft.  My point here is that game improvement sets are made to get the ball in the air as easily as possible, but that has the negative side effect of lessening your ability to control how high or low you want to hit the shot.  If you want to truly take control over your ball flight, you need to play a forged set, whether they're blades or slight cavity backs.  Sure, they're harder to hit, but if you can find a sweet spot, you can hit them...I promise.
 
Now, I see four main elements that affect a ball's trajectory.  The first is the club's loft.  Obviously, the more loft, the higher it goes.  Keep in mind that any degree of the face being open or closed at impact will in effect greaten or lessen the loft of the club. 
     The second element is the club's path on the vertical plane at impact.  You can either be hitting down on the ball, hitting it level, or hitting slightly upwards on it.  Here's a tip...don't ever hit "up" on a ball with an iron.  It's good with a driver, but with iron clubs you will almost always blade the ball.
     The third element is the amount of backspin imparted on the ball.  Any shot that flies has some degree of backspin.  The greater the backspin, the higher the ball will fly.
     The fourth element is the speed of the ball.  A ball that is traveling faster will undoubtedly rise farther into the air than a slower one, for the simple reason that it's flying faster on its launch angle.
 
I don't think I need to discuss any further on the role of the club's loft in producing higher or lower ball flight...that's fairly self explanatory.  But now let's talk about how to effectively hit a low shot and a high shot.
 
LOW SHOT
 
So if you always hit a really high ball and hate how it gets caught up in the wind (or maybe in the trees you were trying to stay under), you need to learn to hit a lower shot.  I had to do this out of necessity when I moved to Texas, because with the kind of wind we get here north of Dallas, you can't play golf with a high ball, period.
     I'm sure most of us could hit a low ball if we really wanted to, by hitting a punch shot with a 4 iron or something.  But how do you get, say, a full shot with a 7 iron to stay lower without ballooning?  Well, the answer is backspin, believe it or not.  But didn't I say that backspin makes a ball go higher?  Yes, I did.  But our goal here is to actually make the backspin do most of the work of getting the ball in the air, without any added help from the club's loft.  To do that, we need to hit down on the ball.
     What does hitting down on the ball do?  Two things:  First, you're delofting the club.  If you're hitting a 7 iron, by hitting down on the ball and leading the club slightly with your hands, you've turned the club into a 6 iron.  The second thing it does is compress the ball against the ground, which puts more backspin on the ball (the ball stays on the clubface a little longer), and this sends the ball flying.  In this way, the backspin is doing more of the work of getting the ball in the air, because by delofting the club you're obviously not helping the ball get airborne.
     Okay, so how do you hit down on the ball?  I do three things.  First, I play the ball back about an inch farther than normal in my stance.  This helps ensure that I catch it on the way down.  Second, I slow down my swing.  Remember that the faster you hit the ball, the higher it's going to fly simply because of its sheer speed.  Slowing down will make the ball "cool it" and stay lower.  Thirdly, I keep my hands low through the hitting area.  You don't want to finish your swing early here, because if you pull up on the club you're going to inadvertently pull the ball up with it, and you're back to a high shot.  So keep your hands low, and extend through toward the target after impact, rather than up.  You want to take about a dollar-bill-sized divot here.  For a great example, here is a link to a Ben Hogan clip on YouTube: http://www.youtube.com/watch?v=Fsl7aozegEM&feature=related  ...when it switches to the face-on view, notice how he keeps his hands low after impact.  Ben loved to play a low fade most of the time.
 
HIGH SHOT
 
Okay, maybe you want to hit the ball higher.  This can be useful when you're playing with a following breeze, need to carry obstacles, or other similar situations.  Or how about hitting those long irons?  Ever wonder how Jack could hit a 1 iron higher than most of us can hit a pitching wedge?  Having the ability to hit high long irons when needed is a tremendous asset.  Here's how I hit it higher.
     To hit a high shot, we need to contact the ball on a more level path, rather than hitting down on it.  This will put the maximum amount of loft on the club.  To do this, I do a couple of things:  First, I play the ball forward about an inch farther than normal in my stance.  This helps keep me from hitting the ball on the way down, which would deloft the club.  Second, I speed up my swing.  Whenever I say speed up my swing, I don't mean to assault the ball.  I simply make a slightly faster turn through in an effort to get the ball flying just a little faster and higher.  Third, I extend to a high finish.  THIS is the big one here.  By finishing high, you are going to effectively pull the ball up more.  You also don't want to take much of a divot, if at all...you just want to shave off the top layer of grass.  For an example, here is Jack Nicklaus during his fantastic '86 Masters Sunday round.  He's hitting a 3 iron, if I recall, and notice first his high finish, and then also the absence of a divot...you can see he's only made a friction mark on the ground: http://www.youtube.com/watch?v=w81j8dXzHQI&feature=related
 
I wrote about another way to lower your ball flight in my previous blog about playing into the wind.  It's a different approach that produces a different type of shot, but let me talk about it quickly here.  If you are in need of a low shot with little backspin that will hit in front of the green and roll up, then go two clubs up (if it's a normal 7 iron shot, use your 5 iron) and choke all the way down.  This actually makes your 5 iron the length of a 9 iron, so you are going to automatically have less clubhead speed (remember how I said that less clubhead speed equals lower flight).  The lower loft of the 5 iron will even out the distance differential, and give you about a 7 iron distance...but the shot will land in front and roll on, rather than carrying all the way to the green.  Try not to hit down on this shot either--we don't want excess backspin here.  Follow the steps for hitting a high shot...the low loft and short shaft will take care of keeping the ball down.
 
Whew!  What a lengthy subject!  Let me know if you have questions.