When working with Ground Reaction Forces, we tend to focus on the basic concepts of magnitude of force, timing, and point of application. These concepts are very important to optimizing the use of the ground. However, when we start to look deeper at how these forces interact to help the golfer create a powerful golf swing, there are many more concepts at play. One of these concepts relates to creating rotational torque between the center of gravity of the player’s body and the golf club. We call this concept a Moment Arm.
In Physics, a moment arm is simply the distance between the center of gravity of an object and its center of rotation. The larger this distance, the greater the amount of torque that is produced. Think about the last time you had a flat tire and needed to remove the hubcaps from the wheel on your car.
Obviously it is very hard to turn the bolt with your hand. However, the larger the tire iron you are using, the easier it is to remove the bolt. This is because you can apply more torque to the bolt by applying force further away from the axis of rotation. You have created a larger moment arm.
The equation here is pretty simple
Torque = Force X Moment Arm
Torque is represented by a unit called Foot-Pounds. So, if you have a wrench trying to turn a bolt, we can calculate how much torque is produced by knowing the amount of force applied and multiplying it by the length of the moment arm.
In this example, we have a wrench that is 6” long and are going to apply 10 Lbs of Force.
.5 Feet X 10 Lbs = 5 Foot-Pounds of Torque.
Now, let’s see what happens when we apply a greater amount of force.
.5 Feet X 20 Lbs = 10 Foot-Pounds of Torque.
Now, instead of applying more force, let’s increase the length of the moment arm. Let’s use a long wrench that is a total of 2 feet in length.
2 Feet X 10 Lbs = 20 Foot-Pounds of Torque.
This is important for the golf swing because it is often difficult to apply a significantly larger amount of force. However, it is often very possible to create a much longer moment arm.
Let’s take a look at a point in the golf swing where this comes into play in a major way. This occurs during the transition of the swing, when we are trying to make the golf club change direction. In order to do this, we have to apply force to the golf club making it slow down and then accelerate the opposite way. I am going to illustrate this with 2D images below. Please note that this is a 3D characteristic and you need to imagine the distance from the CoG in a 3D space.
Let’s look at two players: Cody Blick who plays on the Korn Ferry Tour and Cheyenne Knight who plays on the LPGA Tour.
In many ways, both of these players have nice looking positions at the top of the backswing. When we overlay their ground forces, create the resultant force vectors and relate this to their CoG, we can see a very different scenario.
Again, I will remind you that it is important to think of this in a 3D space. However, as you can easily see, the small black line (moment arm) is much longer in Cody’s swing than in Cheyenne’s. She is using a much smaller wrench to get the golf club changing direction. When you ask players who have a tiny moment arm, they typically will tell you that they are “trying very hard to make the club change direction” or even feel that they are trying to swing the club as fast as possible.
So how do you increase the length of your moment arm during transition? The answer is really not as hard as it would seem in most cases. The primary issue we see tends to deal mostly with lateral force production in the trail leg leading up to the transition. If you don’t create enough lateral force, the overall resultant force vector does not push enough toward the target. This tends to create a small moment arm. Obviously greater magnitude and earlier timing of vertical force on the lead leg can also be a big contributing factor. The moral of this story is that if it feels like you are swinging as hard as you can and you still aren’t creating a lot of swing speed, learn how to get a bigger wrench!