What happens to a golf ball when you putt across a curved ridge? This article removes the mystery to give you a clear picture of what happens.
Edge of a Ridge
In Comprehensive Keys to the Green, you learned how the golf ball moves when it travels across a ridge. Perhaps the most counterintuitive situation was a ball moving up to the edge of a ridge, which will appear to break “uphill” as it crosses over the edge.
In that book, straight ridges were displayed to illustrate the principles. But a few weeks ago I was doing some short game work with a friend when I came across a curved ridge. The results I was getting baffled me, at first. Partly, it was because I hadn’t noticed that the ridge was curved. But partly, too, there were a few things about curved ridges that I needed to figure out.
I’m happy to say that enlightenment dawned, in the end. This post shares those understandings.
Here are the types of curves you’ll run into:
- Cup – A ridge that is concave, or “scalloped”.
- Saucer – A ridge that is convex, like the edge of a saucer.
- Bowl – A concave ridge that goes all the way (or mostly all the way) around.
- Knob – A convex ridge that goes all the way (or mostly all the way) around.
Think of a waterfall like Niagra Falls, where the center of the curve is recessed. When putting from the above the cup, the lines of descent tend to converge. So if you’re off a little it doesn’t matter as much — the ball will tend to arrive at the same place.
When you’re putting from below the edge, on the other hand, the lines tend to diverge as they cross the edge, radiating outward away from one another at the edge. So where the ball finishes can change a lot, depending on your line. Small differences in your line make a larger difference in the result, so putting up to the edge of a “cup” can be fairly mysterious. (That was the situation that motivated this post!)
A saucer is the inverse of a cup. It’s rounded like edge of a plate, where the center of the arc is farther forward, and the edges are farther back.
The path of the ball as it passes the edge is the inverse of a cup, as well. When you’re putting to the edge of the saucer from above, the lines of descent tend to diverge at the bottom. When putting to the edge from below, they tend to converge at the top.
Also known as a “collection area”. Balls that go into the bowl tends to collect in the center of the bowl, at the bottom, because all lines of descent into the bowl converge to a single spot, or small area. If the greenskeeper is being friendly, the cup is at the bottom of the bowl, and life is good.
This could be called a “dispersal area”, because a ball going across the top of the knob could wind up just about anywhere. If your ball is actually on the knob, though, it’s the same as putting over the edge of a saucer — and you already know that balls on slightly different lines will tend to diverge, in that situation.
The more interesting situation — and the one that causes the feature to be called a “knob” — is where you are putting across the knob to get to the hole.
The way you approach that situation is by picking the point at which the fall line on the far side of the knob leads to the hole. That is the point your aiming at. If you can get the ball to that point with just enough speed to trickle over the edge, gravity will take the ball in the direction of the hole.
If you’re off, of course, the dispersion factor comes into play. So the farther away the ball is from the ideal location, the far away from the hole it goes.
But the good news is that if you picked that point well, and selected a reasonable line to get there, you can be helped a bit by the fact that the lines converge when they get to the top edge of the know. The trouble, of course, is that they will tend to converge in the center of the knob.
Whether the knob has a slight dome at the crown, or slight depression (small bowl), the lines will tend to converge at the center. But after they reach that point, they will diverge again!
In other words, putting over a knob is tricky! Both line and speed will be critical. So if you wind up far from the hole, don’t beat yourself up too much. Coming close may be just as much a matter of luck, where any errors in your line just happen to be compensated for by errors in speed, and vice versa!
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