[no_mind_golfer]

nm golfer

I agree 100% with what you state about the circle of an ellipse.

I drew those yellow lines because so many people think that the clubhead swingarc is circular, and they also believe that the body's swing center is the center of that circular clubhead arc.

Well it ain't circular and the center of curvature probably isn't static or loctated at that particular location so to me those lines are meaningless. We'll never all agree on the whys and wherefores of the golf swing and that's ok.

You wrote-: "The centripetal force always points in the direction normal (perpendicular) to the path at any instant towards the instantaneous center of curvature. That location would rarely if ever be a golfer's body part (left shoulder... spine etc....) Its a location in space determined solely by the path of the object."

Exactly! That's the point that I have been making all this time.

Oh... we agree then. The centripetal component of the shaft axial load is always directed at the instantaneous center of curvature.

You also wrote-: "Also... as the words "centripetal force requirement" imply, its something that is required to keep an object rotating but not something that does work (force through distance = work) or stores energy."

I think that centripetal force must do some work if it changes the direction of movement of an object (traveling at a constant speed) from a straight line path to a circular path. Force is surely needed to centripetally accelerate the object so that it moves more centrally (towards that instantaneous center of curvacture) while it is traveling at a constant speed.

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

So for a force to do work it must move the mass through a distance otherwise no work is done. Lets say you tie a rope to you car bumper and you try to roll your car down the driveway but you forgot you left the parking brake on. YOU try like hell generating a big tension force in the rope but the car doesn't budge. How much work did you do? Your body and mucles may think you did alot but the answer is none.

You release the parking brake and try again. You put 100 lbf tention on the rope and roll the car 20 feet before collapsing of exhaustion. How much work did you do? 100*20 = 200 ft-lbs of work

Now lets say your wife was timing you and she watch you struggle for 20 seconds before bursting in to laughter when you collaped. How much power did you put out?

100lbf * 20 ft / 20 sec = 100 (ft lbf/sec) / 550 = 0.18 horsepower

I agree that CP force cannot store energy - the CP energy is in constant use if the object continues to travel along a circular path (if it is constantly being centripetally accelerated).

Jeff.

See above ... the CP (acceleration) which becomes a force when we multiply by the mass (of the clubhead) does no work. It uses NO energy. Its merely that component of the force in the shaft that is required to keep the clubhead rotating. The CP force neither creates nor stores nor destroys energy. Its what needed to facilitate the motion ... a kinematic requirement ...

Now...

This is where it gets confusing and interesting... If said golfer supplys more force in the centripetal direction than is needed to maintain the rotation then the club head mass will begin move towards the center of rotation (zeta dot is non-zero in the equation shown) and consequently theta double dot (angluar acceleration) increases compensurately:



Better golfers can inject an extra bit of energy (excess force in the centripetal direction) which translates directly into angular acceleration (theta double dot) which translates directly to increased club head speed. This is that parametric acceleration I keep harping about lately. Its why Jaime and Boomboom and little Alexis Thomson are all pulling up at the last second.