Doing my dead-level best to generate Lag Pressure, and . . .
Trace that Straight Plane Line.
If only I had known . . .
Originally Posted by jeff
The different hand delivery paths get their separate identity from rhythm --- the rhythm between the i) torso rotational movement (including secondary axis tilt variations) and ii) the left arm rotational movement at the level of the left shoulder socket (including variations in left arm/hand plane shift during the left arm's rotational movement). Varying rhythm produces variably-shaped hand arc paths, and some of those hand arc paths are not perfectly circular in nature.
Well no... energy is not stored (or conserved). The golf swing is not very efficient. We do the backswind to establish "potential" energy ....a small amount of gravitational rho*g*h and a whole lot of musclar-skeletal "P.E.". The backswing is like putting "fuel" in the muscular-skeletal engine.
The stored energy I was referring to - its's nothing more mysterious than the swing speed at any time of the downswing. To be picky it's mass * speed^2 but it basically deals with the gradually build of swing speed throughout the down stroke.
This is very basic fysics. And perhaps the point is so self-evident that you looked for something more "exotic" in my statements.
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Once the downswing begins muscles fire, the linkage begins moving and eventually some 22% (Nesbit) of that potential energy gets converted into Kinetic energy (1/2 m V^2) concentrated at the head of the club. None of it really ever gets stored (for long) or in a benificial way (i.e. club shaft bend doesn't help us).
The kinetic energy you are mentioning here is what I am basically conserned with. You are correct that it doesn't get stored for long. A significant part of it is spent at impact and the rest is wasted shortly after.
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Like Wishon I believe "shaft kick" is a myth.
I have a really *big* problem seing how extensior action can be executed without loading the shaft. And shaft that is being loaded will reload when the moment is off.
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Now setting all of this aside.....
It is quite possible in the "optimal" (if there is such a thing) golf swing there is a point on the golfer's body that remains steady (motionless). I have no problem with people calling that a swing center or what ever as long as they realize is highly unlikely that this spot is where "centripetal force" gets directed for anything other than an instant and probably then just by coincidence.
The two-lever system complicates things. But if you're driving the primary lever around a quiet center - and if the primary lever is driving the secondary lever - I think it makes sense to speak of a swing center.
Further, I do not see a significant upside in moving this swing center around much.
Good golfers + instructors introduces all kind of "tricks" to hit the ball furter. And a lot of ordinary golfers gets confused. X-factor, late release and your "jump on your toe" by the end.
The reason I think the concept of work and energy storage is important in understanding the golf swing because:
1) As long as we can (more or less) accumulate energy until impact, it doesn't matter whether we energize the swing early or late. I don't regard the "late hit" as a magic formula for increased distance for instance.
2) Not even the purest swing is all about centripetal acceleration. Centripetal acceleration only helps us store the energy. We need to actively rotate mass to build swing speed. Tangential forces must be applied. Centripetal acceleration feels powerful but it doesn't add power.
3) A lot ofthe magic mystery moves that is supposed to increase swing speed is misleading.
A stroke pattern that enables the golfer to apply max tangential forces throughout, and at the same time provide the required centripetal force to carry the m*v2 until impact is as good as it gets as far as swing speed is conserned. If that doesn't produce enough swing speed it's time to hit the gym.
"Let's make the geometry simple, if anyone else is going to learn anything. And, we'll consider the center of the circle the left shoulder, since it's the top of the radius. Let's call the left shoulder "A". We'll call the hands "B" and the clubhead "C".
Scenario #1, Hands:
If the distance between "A" and "B" remains somewhat constant (Extensor Action), "B" should inscribe a circle on a piece of paper, like a compass. If we complicate it by letting "A" move (like the golf stroke), the circle becomes somewhat elliptical."
In your mind, the hand arc's 3-D movement in space should be dominated by the movement of B in a circular rotational arc around the axis point of A, which theoretically should produce a circular hand arc. However, you are minimizing the importance of the independent movement of A as significantly affecting the shape of the hand arc - when you write "somewhat elliptical". The reality is that the independent movement of A dominates the early downswing.
In the early downswing, the pelvis shift movement pulls the power package assembly intact all the way down to waist level - without significant separation of the left arm from the chest wall (PA#4 remains loaded). That means that there is no rotational movement of B around the axis point of A, and most of the hand movement in space is due to the movement of the left shoulder socket (A).
You can see that phenomenon is Ben Hogan's swing here.
Look at how much Hogan's hands move down in the early downswing - without any rotational movement of B around the axis point of A as a result of the release of PA#4. The loaded/intact left arm flying wedge's relationship to the left shoulder socket remains unchanged until the hands reach waist level, and it is only then that PA#4 releases allowing B to rotate around the axis point of A in a circular fashion.
The same phenomenon can see in this bird's eye view series of images.
Note that the left arm-shoulder angle remains roughly the same during the early downswing (I incorrectly placed the apex of that wedge in image 1 which makes the angle look wider) - until the hands get down to waist level.
That means that the first part of the hand arc (in the early downswing) essentially doesn't involve any rotational movement of B around the axis point of A (due to the release of pA#4), and is mainly due to the independent movement of A. That's why the hand arc is generally U-shaped, and not circular.
Jeff.
Jeff - "In your mind"
Thank you for letting me know what I had in my mind. I had no idea.
It still doesn't justify the statement that you made and I quoted. I included the movement of the left shoulder in my statement. You've still omitted the ever changing distance between the left shoulder and the clubhead.
If you're choosing to speak specifically about the Start Down, that's one small part. The "more circular" statement was vague at best, and it's still lacking.
I am puzzled when you state that the clubhead arc is likely to be less circular than the hand arc because of the following problem - the everchanging distance between the left shoulder and the clubhead.
I suspect that you don't spend much time studying golf swings using a swing analyser program and that you don't plot the clubhead arc and hand arc to see what is really happening.
The clubhead arc is amazingly circular in reality, compared to the hand arc.
Here is a strobe photograph showing the clubhead and hand arcs.
Note that the clubhead arc is much more circular than the hand arc.
Here is a composite photograph of Aaron Baddeley' swing.
Note how circular the clubhead's path is in space -despite a varying distance from the clubhead to the left shoulder.
I have previously posted photos of the hand arc of Tiger Woods, which shows an U-shaped hand arc.
Here is Sergio Garcia's hand arc.
Even when taking into account the camera perspective distortion problem (due the camera not being perpendicular to the plane of the clubshaft and the plane of the hand motion), it should be readily apparent that the clubhead arc of a good golfer is more rounded than the hand arc.
I like your mathematical expertise when dealing with problems in golf physics.
However, sometimes you get it wrong.
You wrote-: "Nope.... sometimes forces do no work and when the don't do work they can't contribute power (or store energy)
Lets step back.
Work is Force X Distance (has units of energy)
Power is Work / time."
Your formula is wrong when you state that work = force X distance.
One also needs to consider the work force needed to stay in balance when moving in a circular manner. Centripetal force is constantly operating to keep an object in its circular track while traveling at a constant speed - and if the centripetal force is operant, then it is contributing to work (energy) output by preventing the object from flying off its circular path.
Consider two cars having a 100 miles race. Car A has to travel 100 miles on a straight track. If car A completes the race in 1 hour by traveling at 100mph, then car A has expended a certain amount of energy (work output) to complete the race in 1 hour. Now imagine car B having to travel 100 miles on a circular track. If car B completes the race in 1 hour by traveling at a constant speed of 100mph, then car B has expended much more energy (work output) in the same time than car A. The extra energy was expended in trying to keep the car on the circular track at all times while it was racing around a constantly present amount of road bend at 100mph. That extra energy is the centripetal force energy required to constantly centripetally accelerate the car (to constantly keep the car moving along a circular path, rather than a straight path).
I don't know "fysics" but I do know PHYSICS and to be very picky in this case speed and velocity are synonymous. You say speed I say velocity we get the same answer.
Energy doesn't get banked (stored ... dollars in an account) ... the downswing converts potential energy to kinetic. Forces across levers create movement.... that's kinetic energy.
As for the rest... you are entitled to your beliefs. Some people never stop believing in Santa Claus or the tooth fairy. Now we must now agree to disagree.
Originally Posted by BerntR
nmg,
The stored energy I was referring to - its's nothing more mysterious than the swing speed at any time of the downswing. To be picky it's mass * speed^2 but it basically deals with the gradually build of swing speed throughout the down stroke.
This is very basic fysics. And perhaps the point is so self-evident that you looked for something more "exotic" in my statements.
The kinetic energy you are mentioning here is what I am basically conserned with. You are correct that it doesn't get stored for long. A significant part of it is spent at impact and the rest is wasted shortly after.
I have a really *big* problem seing how extensior action can be executed without loading the shaft. And shaft that is being loaded will reload when the moment is off.
The two-lever system complicates things. But if you're driving the primary lever around a quiet center - and if the primary lever is driving the secondary lever - I think it makes sense to speak of a swing center.
Further, I do not see a significant upside in moving this swing center around much.
Good golfers + instructors introduces all kind of "tricks" to hit the ball furter. And a lot of ordinary golfers gets confused. X-factor, late release and your "jump on your toe" by the end.
The reason I think the concept of work and energy storage is important in understanding the golf swing because:
1) As long as we can (more or less) accumulate energy until impact, it doesn't matter whether we energize the swing early or late. I don't regard the "late hit" as a magic formula for increased distance for instance.
2) Not even the purest swing is all about centripetal acceleration. Centripetal acceleration only helps us store the energy. We need to actively rotate mass to build swing speed. Tangential forces must be applied. Centripetal acceleration feels powerful but it doesn't add power.
3) A lot ofthe magic mystery moves that is supposed to increase swing speed is misleading.
A stroke pattern that enables the golfer to apply max tangential forces throughout, and at the same time provide the required centripetal force to carry the m*v2 until impact is as good as it gets as far as swing speed is conserned. If that doesn't produce enough swing speed it's time to hit the gym.
Last edited by no_mind_golfer : 12-24-2008 at 12:20 PM.
Work ONLY gets done when it causes kinetic energy to change. If D (distance) is zero, no work gets done. Centripetal acceleration does not change the kinetic energy of a rotating body. IT DOES NO WORK.
Originally Posted by Jeff
One also needs to consider the work force needed to stay in balance when moving in a circular manner. Centripetal force is constantly operating to keep an object in its circular track while traveling at a constant speed - and if the centripetal force is operant, then it is contributing to work (energy) output by preventing the object from flying off its circular path.
Consider two cars having a 100 miles race. Car A has to travel 100 miles on a straight track. If car A completes the race in 1 hour by traveling at 100mph, then car A has expended a certain amount of energy (work output) to complete the race in 1 hour. Now imagine car B having to travel 100 miles on a circular track. If car B completes the race in 1 hour by traveling at a constant speed of 100mph, then car B has expended much more energy (work output) in the same time than car A. The extra energy was expended in trying to keep the car on the circular track at all times while it was racing around a constantly present amount of road bend at 100mph. That extra energy is the centripetal force energy required to constantly centripetally accelerate the car (to constantly keep the car moving along a circular path, rather than a straight path).
Jeff.
NO BOTH CARS EXPEND THE SAME ENERGY. However the car on the track's tires would show more wear DUE TO FRICTION (the force that provided the click->centripetal force requirement )
Last edited by no_mind_golfer : 12-24-2008 at 12:21 PM.
Reason: try to get hyperlinks to show
Sorry. I cannot accept your explanation. You eliminate the possibility of using centripetal force as being part of your work output equation by framing your equation in that manner. If you "a priori" exclude centripetal force, then obviously it seems that centripetal force doesn't require energy to become operant. The energy may not be utilised to generate forward momentum (forward kinetic energy) along the race track (in the car example), but energy is required to keep the car on a circular track (and the car's tires know that).
Consider a simple example.
Imagine traveling in a NYC subway car that is traveling at 40mph on a straight rail track. Imagine that you are standing in the center aisle and holding onto a vertical post. Then imagine what happens when the subway car goes around a tight bend at the same speed. You will have to hang onto that vertical post for "dear life" to prevent yourself from being catapulted down the length of the subway car. It requires "energy" to remain stationary in balance and that energy is the energy required to offset a centrifugal force acting on your body. I would imagine that the subway car also needs to expend energy to stay in balance on its circular track, and that energy is centripetal energy.
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