Taking a moment

I'm no physicist, but sometimes something about physics resonates. This time it's the science of kinetic energy. I'm not going to define this (look it up), but instead focus on one area of kinetics that has interesting implications for the golf swing - Moment of Inertia (MOI).

MOI is, broadly speaking, a quantity representing a body's resistance to acceleration, which is essentially mass times the square of the distance from the body's rotational axis. It relates to golf because mass, rotation, acceleration, resistance, distance from an axis are all relevant elements.

As I said, I don't really understand the physics all that well, but I don't need to get beyond some observations that are readily accessible to the lay person. Except in super slow motion, the golf swing is quicker and harder to observe that some other sporting activities, so let's look at ice-skating.

Out on the ice, the skater pirouettes slowly with arms out wide and then slowly but surely brings their arms in closer to their body. As they do this, the speed of their rotation increases until with their arms tucked in close to their body their rotation becomes a blur. This is a clear illustration of MOI.

With their arms out wide the mass of the skater is more widely distributed than it is when their arms are tucked in close to their body. By moving their arms in closer as they rotate they are moving their mass closer to the axis of their spin and reducing the inertia to their angular rotation.

In golf, if the downswing is wide, where the mass of the golfer is spread wider, the inertia (resistance to acceleration) is increased. A tighter downswing, where the mass is closer to the axis of the rotating golfer, the inertia (resistance) is reduced. This goes against many simplistic statement about 'keep width in the swing' and 'accelerate the clubhead'. Unfortunately, many good golfers, even teaching pros, do not understand what they are in fact doing to generate high clubhead speeds.

Concepts like 'holding the lag' and 'swing inside to out' are at best marginally relevant, and at times actually harmful to good golf. It's fortunate that the instincts which good golfers have about a good downswing usually coincide with the physics of what happens. Taking that club back wide and then rotating with the arms progressively closer to the body as the clubhead approaches impact is very effective in maintaining the acceleration that occurs prior to impact.

Average golfers, many of whom swing 'over the top' with a wide downswing, are limiting their potential, their capacity to generate such high clubhead speeds. You can drive a ball 200 yards with an 80mph or so driver clubhead speed, but you need 100mph plus for 250 yards or more. Visually, there is not a huge difference in those swings, but listen to the sound of the ball on club and watch the ball flight, the difference is huge.

There are other factors in play, of course, some golfers are stronger, younger, more coordinated, have better timing, more accurate swing planes, whatever, but qualities like strength only take you so far. Just like the ball doesn't know who is hitting it, the clubhead only understands physics.

And this physics is why many small women can outdrive big strong football players; not just because of much vaunted technique and timing, but because physics is working for them. So take a moment and think about that.