Physics

[Michael Lee]

Okay, so now I'm convinced it is the momentum of the club-head or swing speed that is important ( F = m v / t ).  But then, how can the club start motionless at address (zero net forces acting upon it), to something moving at say 90 miles per hour?  The club-head must accelerate in order for it to change speed, thus the players body must be applying force on the club in accordance to Newton's second law that force is directly proportional to the acceleration of an object ( F = m a ).

Since, dare I say, the club also comes to a stop at the top of the swing, even if briefly, a force must be applied, in the downswing, to the club with the player's hands, arms, shoulders, hips, etc.  In other words, the club must accelerate through the swing and hence how important maintaining one's grip is.

Agree?

[Slice of Life]

Originally Posted by Michael Lee

Okay, so now I'm convinced it is the momentum of the club-head or swing speed that is important ( F = m v / t ).  But then, how can the club start motionless at address (zero net forces acting upon it), to something moving at say 90 miles per hour?  The club-head must accelerate in order for it to change speed, thus the players body must be applying force on the club in accordance to Newton's second law that force is directly proportional to the acceleration of an object ( F = m a ).

Since, dare I say, the club also comes to a stop at the top of the swing, even if briefly, a force must be applied, in the downswing, to the club with the player's hands, arms, shoulders, hips, etc.  In other words, the club must accelerate through the swing and hence how important maintaining one's grip is.

Agree?

Easy...you move it. lol

It's been a while since I've been in physics, but your body does "work" on the backswing (in this case, torque multiplied by the angle I think), which in turn creates potential energy since you're hips and shoulders are rotated. Using that potential energy as well as gravity, the clubhead accelerates on the downswing and generates its speed.

Something like that.

[Michael Lee]

Originally Posted by Slice of Life

Easy...you move it. lol

Oh, how keen and clever you are :)  But think about Newton's first law, a body at rest will stay at rest unless acted upon by an outside force.  When I first heard this in high school, I thought "well duh"

[Slice of Life]

Originally Posted by Michael Lee

Oh, how keen and clever you are :)  But think about Newton's first law, a body at rest will stay at rest unless acted upon by an outside force.  When I first heard this in high school, I thought "well duh"

Like I said, move it. You're the outside force.

[iacas]

Originally Posted by Michael Lee

The club-head must accelerate in order for it to change speed, thus the players body must be applying force on the club in accordance to Newton's second law that force is directly proportional to the acceleration of an object ( F = m a ).

Agree?

Read the posts before this in the thread, where I stated (or was quoted as saying) these same things (in longer form).

Geez.

[Michael Lee]

Originally Posted by iacas

Read the posts before this in the thread, where I stated (or was quoted as saying) these same things (in longer form).

Geez.

Okay, no problem.

[DownAndOut]

Reading through this thread has been entertaining but all the equations regarding conservation of linear momentum between club and ball are contained on the web. 

Tutelman's website says
Coming into impact, a golf club's kinetic energy is based on its mass and speed. It gets there from zero kinetic energy during the time of the downswing, less than half a second. This implies that the muscles have to put out a certain amount of power for half a second. Physiologists know how much power a muscle can provide for a short burst (say, half a second).

When this fairly simple calculation is cranked through, the answer is that over 30 pounds of muscle mass is needed to impart that energy to the golf club. This is muscle that is engaged in generating motion, and does not include muscle used to stabilize the body in the golf swing posture. The 30-pound number has come up consistently in quite a few separate studies aimed at this question.

There isn't anywhere near that much muscle in the forearms, hands, and wrists, so they can't be the major driving force of the swing. You need the big muscles -- the legs, thighs, torso, and shoulders -- to create that much power. That verifies that the clubhead's energy comes from body rotation, not hand torque. But it doesn't unambiguously point to centrifugal force as the enabler.

But we should be able to compute the clubhead speed that would result if we only used body rotation and not centrifugal force. Without any velocity at impact from uncocking the wrist, just from body rotation, we get only about two thirds the clubhead speed that a good swing actually accomplishes. So we need centrifugal force because:

• We know the bulk of the power comes from body rotation.
• We know that body rotation without wrist-uncock velocity gives a third less clubhead speed.
• In order for body rotation to generate wrist-uncock velocity, we need centrifugal force -- because the small muscles in the hands and forearms can't generate that much power.

But have some of these scientists made wrong assumptions when creating their improved models of the golf swing?

Can we question whether assumptions about 30Ib non stabilising muscle type rates of contractions are correct ? This is where they have assumed that the body is used to power the swing (mainly by rotation and centripetal pulling forces) because the arms don't have that amount of muscle.

But did they take into account that fast twitch 11x muscles contract 10 times faster than slow type 1 (stabilising muscles) and that type 11a muscles contract approx 2 times faster than type 1?

Did they also take into account how much muscle and their distribution type in the human anatomies varies with age and activity habits?

How does this affect us golfers if some of these assumptions are wrong and have been incorporated in golf instruction by PGA ?

1. If the scientists have overlooked the fact that there are enough fast twitch 11x muscles in the arms (in the average sedentary human) to hit the ball a long way, then the 'body powers the swing ' instruction could be wrong (for your body type). Maybe golf instruction needs to also consider using mainly the 'arms/wrists/hands' in providing the extension, rotation to get clubhead speed (for specific muscles distribution anatomies) and using the body in a more stabilising role.

2. Depending on what technique you are using (body , arms , both ) is it compatible with your muscle distribution types?  Older people in their 80's lose almost all 11x type so maybe using your body a little more might be preferable to retain clubhead speed (seems counter-intuitive doesn't it?).

So what do you think powers the golf swing?

 

 

 

[DownAndOut]

Correction below regarding muscle type in younger vs older people (not as clear cut as I thought).

Also for sake of accuracy regarding contraction velocities  (sorry about the yellow highlights as its a cut and paste)

One component of the myosin mole­cule, the so-called heavy chain, deter­mines the functional characteristics of the muscle fiber. In an adult, this heavy chain exists in three different varieties, known as isoforms. These isoforms are designated I, IIa and IIx, as are the fibers that contain them. Type I fibers are also known as slow fibers; type IIa and IIx are referred to as fast fibers. The fibers are called slow and fast for good reason: the maximum contraction velocity of a single type I fiber is approximately one tenth that of a type IIx fiber. The veloci­ty of type IIa fibers is somewhere be­tween those of type I and type IIx.

 

We know that all humans have not only pure slow and fast fibers but also fibers that contain both the slow and the IIa (fast) myosin isoforms or both fast isoforms (IIa and IIx). In the young vastus lateralis muscle these hybrid fibers are scarce: fewer than 5 percent of the fibers contain both the slow myosin I and fast myosin IIa isoform. In our elderly subjects we found that a third of all the examined fibers contained these two myosin isoforms. Astonishingly, this hybrid fiber was the predominant type in the very aged muscle.

 

     We concluded that the question of whether aging muscle has more slow fibers cannot be answered with a simple yes or no. What seems to happen is not a change in ratio be­tween slow and fast fibers but more an obfuscation of the border between slow and fast fibers, so that in very elderly muscle one third of the fibers are neither strictly slow nor fast but rather somewhere in between

[saevel25]

5 hours ago, DownAndOut said:

There isn't anywhere near that much muscle in the forearms, hands, and wrists, so they can't be the major driving force of the swing. You need the big muscles -- the legs, thighs, torso, and shoulders -- to create that much power. That verifies that the clubhead's energy comes from body rotation, not hand torque. But it doesn't unambiguously point to centrifugal force as the enabler.

A lot more than you think comes from the hands in terms of clubhead speed. You can restrict your body turn and hit shots a lot further than you can if you restrict your arm movement and just rotate. 

From this simple test the arms account for 70% or more of the club head speed. 

5 hours ago, DownAndOut said:

1. If the scientists have overlooked the fact that there are enough fast twitch 11x muscles in the arms (in the average sedentary human) to hit the ball a long way, then the 'body powers the swing ' instruction could be wrong (for your body type). Maybe golf instruction needs to also consider using mainly the 'arms/wrists/hands' in providing the extension, rotation to get clubhead speed (for specific muscles distribution anatomies) and using the body in a more stabilising role.

It's not as simple as that. There is something called the "Kinetic Chain". It exists in all athletic movements. From shooting a basketball to hitting a baseball. 

A good kinetic sequencing is a good athletic motion. Before impact the hips, torso, shoulders, and arms should be slowing down. Because of the kinetic chain, if done right, then the clubbed will reach impact at about max velocity. If a golfer flips they are catching the ball way past peak velocity. Good golfers catch it just before or at peak velocity.

There is no isolating one piece of the kinetic chain. The body does power the swing because you swing with your body. 

 

[DownAndOut]

Hi Savel25

Yes, the first paragraph you referred to was from Tutelman (not me).

Your 2nd point about the Kinetic Chain also makes sense but I don't wholly agree with your last sentence

" There is no isolating one piece of the kinetic chain. The body does power the swing because you swing with your body.  "

The body could be moving to accommodate the movement and intention of the arms too. With regards the kinetic chain , I've seen some people hit golf balls while sitting in chairs , etc . but the upper body was still involved somewhat to the intent of the swinging arms (ie. getting out of the way rather than powering the swing).

How your muscles and anatomy are built could determine which parts of your body power the swing and which ones stabilise them (and also dictate how your kinetic chain works).

 

[DownAndOut]

So the above video actually proves that some golf instruction could be wrong with regards 'dog wagging the tail'. If the arms/wrists/hands provide 70% of the swing speed, then centripetal forces via the extra pulling of the arms (using the body) after the release starts must be supplying the rest.  I've heard that centripetal forces could account for an increase in 20% of the clubhead speed at start of release.

Edited December 24, 2016 by DownAndOut

[iacas]

17 minutes ago, DownAndOut said:

So the above video actually proves that some golf instruction could be wrong with regards 'dog wagging the tail'.

That stuff is the realm of "feels," and thus, not something that really belongs in this type of conversation.

Your whole body contributes to the golf swing (maybe not your left earlobe, but I hope you get the point…). Different parts will contribute differently amounts and with slightly different timing, but they all contribute and they all generally contribute in the same general order.

This thread dates to 2006. It was revived in 2013, and now again in 2016.