Endless belt and release physics

[Jeff]

Donn - you wrote-: "Do you buy Homers concept of Longitudinal Acceleration vs radial acceleration?"

I will deal with a swinger's swing - where HK implies that the hands supply a constant pulling force along the length of the club longitudinally (along its longitudinal axis). It is true that as the left hand moves in space it is pulling the grip end of the club in a particular direction, and that the directional force can be perceived to be pulling the grip end of the club along its longitudinal axis. However, the true reality is that the club develops angular acceleration from the very start of the downswing (because the hands are constantly changing direction) and the hand pull cannot therefore remain along the longitudinal axis of the clubshaft throughout the entire downwsing (because the club has inertia and the COG of the club doesn't move instantaneously in the same linear direction with respect to the pulling force). As the downswing evolves, and as the club progressively releases, then the hand pull direction is increasingly at an increasing angle to the longitudinal axis of the shaft.

You also wrote-: "I would think that the blue line from red line 6 to redline 7 would be straight rather that curved. Your curved line appears to suggest radial acceleration. Red line 6 is length wise down to approx hip level. Would this be the point where
pulley starts?"

I don't think that the hand movement arc is ever straight in a golf swing, and that it is always near-circularly curved. I actually think that there is no "pulley" in the hand curve of "real life" golfers (like Tiger Woods and Bobby Jones) because the hand arc curve is essentially C-shaped, with no abrupt changes in direction as would occur with a J-shaped curve.

Jeff.

[Jeff]

Bagger - thanks for commenting.

I agree that although the rope pull is theoretically constant (because the boat is traveling at a constant speed) that the actual pulling force exerted on waterskier number 2 must become greater when the skier angles the skis to the side and moves along a curved path (instead of a straight line path) - because of the resistance of the water. Do you have the know-how to estimate/calculate the magnitude of this greater pulling force at point A, point B and point C - taking into account the facts that the i) waterskier is progresively moving faster as he moves along that curved path, and ii) the rope is an increasing angle relative to the directional movement of the skier?

You also seem to imply that the pulling force felt by the skier at point C would be at its greatest. I would imagine that it is at its least at point C - because of two factors - i) The waterskier is now moving much faster than the boat, and ii) the angle of the rope is nearly at right angles to the direction of travel of the skier. I would think that the pulling force felt by the waterskier would be at its greatest in the earliest part of the curved path (prior to point A).

Jeff.

[Bagger Lance]

Jeff,

I can't help you with the math. Depends on the horsepower of the boat, the effective boat draft, how hard the skier pulls the boat sideways, prop pitch and size, water surface conditions, ski design, rope length, etc. The greater the angle from the center of the boat to point C, the greater the angle of the ski "blade" otherwise the skier is decelerating.

Trust me, not much application to the golfers release but if you want to do the math, there are plenty of resources to put the puzzle pieces together. Not my cup-o-tea, I was only concerned about rounding the buoy's without dropping an elbow or rope in the water. That takes time off the score and ruins rhythm.

Some are Performers and some are Engineers. Rarely the two meet in a single individual, but we need each other collectively. I appreciate what you are attempting here Jeff.

About that left shoulder movement. Can you quote VJ in context so there is no misunderstanding?

Thanks,

[Jeff]

Bagger - you wrote-: "The greater the angle from the center of the boat to point C, the greater the angle of the ski "blade" otherwise the skier is decelerating."

I cannot understand this point. If the curve passing through all the points A,B and C is a defined curve of a certain shape, then the angle of the ski blade must be constant at all times during the skier's passage along that curved path - irrespective of the angle of the skier to the boat. The angle of the rope changes, but the skiers blade angle must surely remain constant if he maintains a curved path of constant curvacture.

What do you want me to clear up about the left shoulder movement? I only made the point that the idea that the left shoulder remains "fixed" in space as the center of a circle with a fixed radius is not what happens in a "real life" golf swing in the late downswing - because i) the left shoulder socket is moving upwards, leftwards and backwards in the late downswing and ii) the distance between the left shoulder socket and the clubhead constantly changes as the clubshaft becomes progessively more in-line with the left arm in the late downswing.

Jeff.

[Bagger Lance]

I've always wished I could combine my passions but I could never reconcile skiing and golfing.

I'm not interested in discussing the skier analogy, but I am interested in your comment regarding VJ's view of Hogan's left shoulder.

"see the three white dots with interconnecting red lines. VJ's representation of Ben Hogan's left shoulder socket as being a single fixed point in space is an oversimplification, and it doesn't represent true reality. It is a gross over-simplification -"

Just want to make sure that VJ's representation is rooted in reality. I haven't read his book so I'm trusting that this statement is fair and contextually accurate.

[Jeff]

Bagger

Here is a copy of VJ's Impact Circle photo from his book.



Jeff.

[BerntR]

Bagger

Here is a copy of VJ's Impact Circle photo from his book.

Jeff.

Edit: Unfortunately I am not able to present it as anything else but a link.



I do not like the impact circle consept, because it makes it seem like the rotation centre of the golf swing is at the left shoulder. Which it woould be if the sholder was kept still.

I've added some "momentum" to the drawing.

The centre of rotation is IMO close to the golfer's nose or neck.

The curved arrow around the golfer's head is momentum created by the rotating body and applied to the left shoulder. This momentum results in a pulling force on the left arm and further on the left club. This force is illustrated with the red arrow above the golfer's shoulder.

Since the sholder is offset to the centre of rotation, the pulling force from the shoulder can be decomposed in a component that is purely radial and another component that is purely tangential. That would be the yellow arrows by the clubhead.

The small arrow at the golfer's right hand is some of the force from extensior action. This could also be described as torque applied to the left arm, which is required to deal with clubshaft vs left arm lag.