What is the Centre of Gravity and Moment of Inertia on a Golf Club?
Thanks to modern technology, golf shots don’t have to be struck in the dead-center of the clubface to produce a decent result. Even the best ball strikers in the world mis-hit their clubs every once in awhile, and they appreciate the extra forgiveness as much as every other golfer.
Perhaps you have wondered: Where exactly does this forgiveness come from? Are certain clubs designed to be more forgiving, and if so, what factors decide that? Do you have to give up other benefits from your golf clubs if you want to minimize the penalty for off-center shots?
To understand these questions better, the most important concepts to grasp are the Center of Gravity (COG) and the Moment of Inertia (MOI), and how they’re utilized in golf club manufacturing.
Centre of Gravity in Golf Clubs
According to the NASA Glenn Research Center website, COG is, “…the average location of the weight of an object.” As it relates to a golf club, the average point of where the weight is located determines the center of gravity. Manufacturers are constantly tinkering with various metals, alloys, and weight placement in club heads, as well as working on different clubhead designs, in order to manipulate the center of gravity, typically trying to move it lower and farther behind the clubface.
Why? Most golfers have trouble getting their ball airborne, and moving the center of gravity farther back and lower promotes a higher ball flight. This is a major reason why you see more emphasis on adding weights on the bottom of woods; in fact, the benefits are twofold. Not only does having the COG farther back help launch the ball higher, it also does so with less spin, which are ideal conditions for increasing distance off the tee.
The size of clubheads also determines COG; not only do they create larger effective hitting areas (sweet spots), they also allow more room to lower and deepen the COG, which will create those distance-producing factors.
The Scientific Design
COG also influences the accuracy of shots as well. The horizontal COG is the determining factor in how much the club will want to stay open. The closer the horizontal COG is to the shaft, the more tendency the club will have to stay more square, and possibly even produce a draw, which most players struggle with.
If you ever look closely at most irons that boast being more forgiving, they will always tend to be bulkier toward the heel than more traditional blade-style irons. Another factor that correlates with golf club design and the accuracy/forgiveness of shots is in the MOI.
Moment of Inertia
In physics, the Moment of Inertia is, in simple terms, a body of a mass resistance to rotation. In simpler terms that apply to golf, when you hit a shot that is off-center, MOI determines how much your club stays stable at impact; the higher the MOI, the less distance and accuracy you will lose compared to square contact.
How is MOI implemented in the design of golf clubs, and how does it relate to the COG? The position of the COG has an inverse correlation with the MOI. While moving the COG closer to the heel will increase the ability to keep the face square, it also creates less MOI, which essentially means less distance, as the club will still tend to twist on off-center twists.
Going back to our example of forgiving irons, notice how there always tends to be more weight distributed away from the center. This is known as perimeter weighting, and is the main way manufacturers seek to increase the MOI of a golf club. With a traditional blade, which have smaller heads, less weight overall, and thinner soles, your chances of getting much help on off-center hits will increase.
How to Choose the Right Club
With all this information, what golf clubs are right for you? It really depends on what your handicap is and what your goals are. For anyone who is not a single-digit handicapper, perimeter weighted golf clubs will make the game more fun by giving you a better chance to hit longer drives and higher iron shots without having to make great contact every time.
For more experienced players, or players looking for the ability to shape the ball easier (which is tougher with clubs designed to stay more stable through impact), traditional cavity-back and muscle-back irons are better suited for your game.
Think About Your Location
There are exceptions to these general rules of thumb. For example, say you live in a predominantly windy area, where your good shots get eaten up by the wind, either into or in crosswinds. In these types of conditions, it’s better to have clubs with higher COG, which will lower the dynamic loft and keep your ball from getting gobbled up by windy conditions.
This also holds true for golf courses that are tight and narrow, with lots of overhanging tree branches.
The Final Word
Physics may not be fun for everyone, but a little bit of knowledge can be useful to make wise decisions when it comes to purchasing golf equipment. Finding the right one for you might take some looking around, but if you follow the advice, and remember the science behind it all, I’m sure you’ll find the clubs of your dreams. Having the right clubs in your bag will make your next round more enjoyable.