Aug 06 2009
Brief Explanation of Moment of Inertia (MOI)
Every now-and-then people ask me to explain Moment of Inertia, or MOI, because they see it in some of our equipment reviews on drivers. I figured if a few people have asked me about it, a lot of people probably have questions about it. So, here’s a quick explanation.
Moment of Inertia, or MOI, is a property of physics that tells you how easy or hard it would be to spin an object around a specific axis (think spinning a basketball on your finger). The harder it is to make an object spin on an axis, the higher the moment of inertia.
Pertaining to golf, all you really need to know is that clubs with high MOI do not twist as much on off-center hits. If you don’t hit the ball in the center of the club face, the club head wants to rotate around its center of gravity, or CG. So, if you hit the ball off the toe or heel of the club and your driver has high MOI, it will be more forgiving and give you better results.
Since golf companies like Nike, Callaway, and TaylorMade have lots of drivers with 460cc club heads, they have plenty of room to move the center of gravity lower and more rearward on the club head, which results in higher MOI.
MOI is also what make hybrids and rescue clubs work. They’re much easier to hit than a low iron because they have a club head like a driver or fairway wood giving the club higher MOI. If you take a 3-iron and a 3-hybrid, the club faces are set at the exact same degrees, but the hybrid will be easier to hit and much more forgiving on off-center hits. The CG of a 3-iron is just behind the club face, but on the hybrid the CG is further back and lower, making it more forgiving.
So, there’s a quick explanation. If you have deeper questions, please don’t hesitate to drop a comment below. I’ll answer you as soon as I can (which is usually immediately because I have no life).
