While “moment arm” may sound like an advanced physics term, it’s actually a simple and powerful principle that helps explain how golfers create torque, and ultimately speed in their swing.
In biomechanics, the moment arm is the perpendicular distance between the line of action of a force and the axis of rotation. In practical terms, it’s the leverage you get when applying force to rotate a joint or an object.
Think about using a wrench to turn a bolt: the longer the wrench, the greater the moment arm, and the less effort you need to apply to produce rotation. The same principle applies in the golf swing.
In response to one of the most asked questions on our YouTube channel, Dr. Greg Rose defines moment arm and demonstrates how a golfer might be able to increase it in their swing.
For another example of “moment arm” in golf, check out this article on Jose Ballester’s unique kinetic data: https://www.mytpi.com/articles/biomechanics/what-you-can-learn-from-the-unique-kinetic-and-kinematic-data-of-the-2023-european-amateur-champ
48 Comments
Or, you just hit it harder!
my favorite part about this guy is he is always out of breath by the end of the video, so you know he does it in 1 take and he gets very active during demonstration
Thanks Greg, one of the best channels out there for sure👍🍻
I would have had better grades if my engineering professor used examples I can relate to 😂
Everything he said is right except for what he said at the very end there. At the TOP of the swing with great players, the spine IS leaning 1 or 2 degrees towards the target, as pressure starts to settle into the left foot. (And the center of mass is not the head). At this point, the force vector is a million miles ahead of the center of mass, and getting farther ahead. THEN, when the left foot pushes into the ground, that is when the spine leaning back away from the target. During the transition, the spine is straight up and down or slight toward the target.
Zero distance=zero moment. The longer the distance the greater the moment. Force doesn’t have to change to increase total moment.
Can't believe I get this content/knowledge for free, thanks Greg🫡
I’m never convinced by this dude.
Thanks for the education, I now understand torque much better. Appreciate you sharing this knowledge. Cheers.
very informative
Been waiting for this
I think I had a moment right now. Excellent teaching
😮😮
Can't argue with any of that, But what about Shear Force? If I were on a Slippery Surface give way to Angular Force. Shouldn't we learn how to Harness this Shear Force in order to assist with the Moment Arm?
Awesome!!!
Wow. My Brain just exploded. So good!
OUTSTANDING EXPLANATION!!! Dr Kwon explains this with 2D software. However, you show it it 3D with the pole. I think your 3D is easier to communicate.
Would like to have a better description of how to apply the theory.
Good morning Dr. Rose. I am following all your content since quite a while and out of this, always understood and thought, that the left food is pushing way more than the right foot. Now seeing the „big hitter“ in your video, he is pushing a lot with the right foot (unfortunately just like me!). did I took the wrong idea out of this study? Regards and please, keep up this work. Edmundus from Romania
still waiting for somebody, anybody to show me how the ground pushes back. The ground never moves and just stays there.
Back in 1933 Abe Mitchell, British Golf Pro wrote a book called “Down To Scratch” and coined the phrase “Swinging into resistance” which is how a TORSION BAR and a rubber band powered balsa wood airplane works and the front suspension on a 1960 Dodge Lancer — our family car — my mechanical engineer father bought because it used torsion bars instead of springs.
Torque is create in a golf swing by squaring the back foot like Ben Hogan taught me to do | which causes STRETCHING RESISTANCE in the muscles of the back leg and buttocks which is what powered his hip turn on the way down BY RELEASING TORQUE create by causing his hips to stop in EXACTLY THE SAME angle every swing via minor adjustment to the flair of his back foot, a cause and effect I discovered back in 2008 when I decided to reboot my Nicklaus modeled swing with his by reading Five Lessons and doing everything he suggested until I got the same result he did, also making screen captures of videos of him and analyzing where his body mass, arm mass, hands and club head mass moved frame by 1/30th sec frame to understand when those masses accelerated and at critical point decelerated.
I was familiar with how centrifugal governors worked on steam engines and how figure skaters control their rate of spin — and balance — in the same way by extending mass of arms equally on opposite sides to slow down and pulling them in an crossing over chest to speed up. The key to staying in balance doing that? Equal mass spinning at the same rate.
But in a golf swing, like the Hammer Toss in the Scottish Game the golf swing is based, the swinging mass on one side must be BALANCED by equal and opposite FORCE — Kinetic Energy. The counter intuitive part is that Kinetic Energy increases with the Square of the Velocity not linearly. What that means is a golf swing is that increasing club head Velocity (V) 2x increases its KINETIC ENERGY (KE) 4x, 3x V = 9x KE, 4x V = 16x KE, 5x V = 25 KE. The same increase in KE occurs moving the body and arms but because their masses are greater then to not need to move as fast to balance the force of the club to keep the balance of the golfer stable, which is critical for accurate ball striking.
In 2008 I was 56 and had retired after a 25 year career in the Foreign Service and taken a part time job as a starter at public nine hole par 25 course where I realizes golfers with perfect swing technique from toes to top of head were being pulled off balance on their toes in their downswings by the HUGE SPIKE in KE which occurs when the lag is released. Getting pulled on their toes tilted the plane of their swings, causing the club head path to move outside the target line and their SUBCONSCIOUS BRAIN reacting by curling their toes down and trying to STEERING THE FACE back to the ball with their HAND EYE COORDINATION saving the shot or not depending how good that way. I realized I was doing the same thing when Sliced or Pull Hooked the ball.
How MOI of the arm +club system relates to this in the downswing is that like the figure skater a golfer can fire the hip with more acceleration and velocity with the club shaft vertical | / and close to the center or rotation than if extended like in the Olympic Hammer Toss. A slight lateral shift of body mass / > / | is sufficient to balance the increasing KE in the mass of the lead arm being pulled down by Gravity the most constant force in nature and keeping the club lagged 👍 and vertical with club head mass close as possible to the center or rotation prevent it from becoming an unbalancing force requiring more forward movement ==> of body mass to counter it.
The problem when beginners ‘cast’ or release lag too soon the club head mass does become and unbalancing force the subconscious brain reacts to by swing it ‘over the top’ which solves the immediate balance problem but creates a new one, the same incorrect outside in path as the pro golfer with perfect swing mechanics who let himself get pulled on his toes in the down swing tilting the entire swing plane like a crashing helicopter 🚁 I did that a lot with my RC model helicopters I was flying there up and down the fairway, how I ‘connected the dots’ of what I was observing intuitively as an INTP temperament.
The point where the MOI of the arm+club changes is the point where 👍 that changes to this 👉: radial to ulnar deviation in the wrists, the same action that snaps the tip of a bull whip past the 700mph sound barrier and tries to accelerate the club head the same way. Turn the club around and whip it and will it move faster and go ‘whosh’ ? Yes because there is less mass to accelerate. But that’s also the point where KE spikes FASTER THAN THE REFLEXES CAN REACT and 99.99999% of golfers get pulled off balance in some swings, more on the course on even lies that on the mats on the range which is why you shouldn’t waste money on range balls, instead find somewhere cheap to play or do like I did, get a job at a course that allows employees to play for free.
Once I CONSCIOUSLY realized it was my reflexes not reacting to the spike in KE as I release the club and getting pulled on my toes at impact the problem was easy to correct. My toes became the ‘canary in the coal mine’ for detecting a lose in balance my brain did not CONSCIOUSLY until I did not finish the swing in balance.
The way I learned to stay in balance was to delay release of lag — keeping the MOI of the arm+clubhead mass low as possible — until when I did release it the FORCE VECTOR of the KE increasing in the club head mass / vvv stayed between my feet — the anchors for balance — and POINTING AT THE GROUND and aimed a few inches ahead of the ball. Releasing the club head that way with a ‘vvvv’ downward KE vector increases stability because it PULLS BODY MASS DOWN at the same time the leg action is lifting the AXIS OF ROTATION of lead arm mass and mass of lead arm also is swinging up and left creating UNBALANCING KE vectors which is why a loss of balance occurs after impact.
Once technique is consistent it’s getting pulled off balance by the KE of the club head mass going somewhere other than at the ground in front of the ball AT IMPACT that causes shots not to go as planned even at the pro level. The key to POWER + Balance is knowing how to release the KE of the club head mass downwards between the feet not out towards the target, what most think the goal of the exercise is.
Hogan said it often and best, “The Secret is in the Dirt.” 😂
It made a lot of sense!
Just, not to me!
That rod should be orange (for effect) to contrast the muted colors.
2:35 Pushing Back Diagonally (trail foot GRF)… And what is the handpath doing at that instant? – sling to swing?
This is what makes golf so tough to learn- Tom Watson & Paddy Harrington recently stated 85%+ of swing speed comes from the hands / arms so that's where our focus should be – Not the body twisting.
Wow!!!
COP Backup?
567,744 swing thoughts added to the others.
This is awesome, great explanation.
Dr. Rose, can you please tell me how ground forces work or are used/applied with a “stack & tilt” golf swing.
I would love if there's was more than one tip center going to California its not that easy!!
are you saying twerk or twork?
THE WORD "POWER" IS USELESS IN GOLF
the world needs a standardized golf instructions
Great stuff! Two questions: where is the centre of mass on a person and, more importantly, if I understood correctly, you push backwards & away from the target on a 45 degree angle or so with the trail foot; how in the world do you do that?
Does this mean that to create more torque, you have to apply pressure when the centre of mass of the club is as far away as possible from your axis. Thus on the top of the backswing?
Amazing tips. Without increasing strength or effort you can improve your results. Spread your legs a touch and don't press straight down press backwards lengthening your moment arm away from your center. Technique and mindset improvement can help the senior golfer to get more effortless power! I guess its also how some baseball hitters have a wide stance and don't stride forward, they push backward on their rear foot while keeping their upper body tilted backward. Whether you take a stride or not you never want your upper body leaning forward in baseball or in golf I guess except maybe in the take away as a momentum starter in the takeaway/backswing.
Can you please make another video on this subject and be more elaborate? Thank you
these videos are so dope!!! keep them coming… so much to learn lol…
I think you will find the ground isn’t pushing back, it’s resisting.
#DrRose4Prez
excellent explanation
Very cool stuff, thank you!
Video comes complete with a session with a chiropractor
Hopefully golf instructors stick with classical Newtonian physics, and don't "progress" to Einstein – if we start hearing about warped spacetime we may give up😅
BUT HOW WIDE IS TO WIDE????
greg, there is no ground reaction force.there is only ground resistance to a force applied to the ground. force is mass times acceleration and that is a newtonian law. force matchematically is a vector. it means it has a direction and lenth in 3d space. the same is true for acceleration which is also a vector the correct term is F=a*m. force equals accelacation* mass and the vector component is expressed with a a small arrow over the letter F and a in physics. if you use physics terms it is important to apply them correctly. otherwise thanks for making the video and trying to explain the golf swing in physical terms! always liked your contant and effort, I just would be cautious to use the right terms with it!
Quality information could you slow down a little please I need time to think