Was Homer Wrong?

[Mike O]

The words centripetal and centrifugal in physics have their dictionary meanings. centripetal=toward the centre, centrifugal=away from the centre. They are equal and opposite, action and reaction.

Most people get it wrong because they do not understand that the centripetal force acts on the stone, and the centrifugal force acts on the string (or the boy). We then get incorrect statements about the centrifugal force throwing the rock out and keeping the string taut and that sort of thing.

What keeps the string taut? The boy pulling on it.
What balances the centripetal force on the stone? Nothing, that's why it moves in a circle.

As a general rule, the more words used to describe the phenomenon,
the more errors will be introduced.

Interesting thread- although it seems like no one can clearly define all the issues/perspectives involved in clearly understanding the topic at hand. Although, some may take that personally- it's more just an observation regarding the thread. And I'm certainly not one who necessarily could clearly define all the issues involved- in fact I'd probably be more off base than most.

Just one piece of the puzzle and confusion- and I could be wrong but in relation to Newton's third law- "action reaction" and the notion of "centripetal" and "centrifugal"- there seems to be some discussion of the boy, string, rock- and some of it appears to me to be on the wrong track.

Newton's third law to me - just says that you can't create a force out of nothing. To me it's similar or it's "sister" concept is that you can't create or lose Matter - it just is. So if you push a car down the street in a straight line- then the equal and opposite force is your feet on the ground pushing against the earth in the opposite direction of the motion of the car. That's a simple example of the action/reaction concept.

I would think the proper context of this in relation to the golf swing would be to look at the "whole system". So imagine that you have the clubhead or rock moving in a straight line- attached to it is a golf shaft or string- now to prevent that thing from moving is a straight line you give a tug on the shaft or string and it curves/moves toward the tugging- that's the centripetal force. So in relation to Newton's third law- you ask what offsets or allows that inward tug to happen? Depending on the movement- i.e. amount of force involved etc.- how heavy the rock is compared to the mover it could be different- but to me the basic reaction forces would be the feet pushing against the earth- that force is away from center and allows the force towards center to take place.

So I'm limiting my comment to the specific issue of action/reaction forces- and I don't see it - in the larger picture - being the boy and the string or the boy and the rock, or the rock and the boy.

Hope I didn't further clutter the post- with something that isn't clear.

[golf_sceptic]

Nice post Mike.

You've got a good handle on things from my point of view, but by looking at the system as a whole (like yoda did with the string) it leaves greater scope for misunderstanding and it is harder to identify where the misunderstanding lies.

There is a nice student exercise that beginning physics students use about a man standing on bathroom scales whilst a lift accelerates upward. I'll run through it if anybody thinks it will help, but to go back to your examples...

If you push on your car the equal and opposite reaction is that the car pushes on you with the same force and in the opposite direction. You push on the earth and the earth pushes back, but this pair of equal and opposite forces will be different in magnitude to the push on car/car pushes back. The second phase of analysis is to look at each object and ask what forces are acting. On the car, your push. On you, the car's push and the ground's push. On the ground, your push.

With the rock and the string, if the mass of the string is important then we can't perform a correct analysis without separating considering the "string on rock/rock on string" and "boy on string/string on boy" pairs separately because they will have different magnitudes. We can't just say "boy on rock/rock on boy" without things getting very muddled.

This is where the man on scales in lift will help if you need more detail.

[Mike O]

Nice post Mike.

You've got a good handle on things from my point of view, but by looking at the system as a whole (like yoda did with the string) it leaves greater scope for misunderstanding and it is harder to identify where the misunderstanding lies.

There is a nice student exercise that beginning physics students use about a man standing on bathroom scales whilst a lift accelerates upward. I'll run through it if anybody thinks it will help, but to go back to your examples...

If you push on your car the equal and opposite reaction is that the car pushes on you with the same force and in the opposite direction. You push on the earth and the earth pushes back, but this pair of equal and opposite forces will be different in magnitude to the push on car/car pushes back. The second phase of analysis is to look at each object and ask what forces are acting. On the car, your push. On you, the car's push and the ground's push. On the ground, your push.

With the rock and the string, if the mass of the string is important then we can't perform a correct analysis without separating considering the "string on rock/rock on string" and "boy on string/string on boy" pairs separately because they will have different magnitudes. We can't just say "boy on rock/rock on boy" without things getting very muddled.

This is where the man on scales in lift will help if you need more detail.

Golf Sceptic- Just my perspective but it appears to me- that you have a significant communication problem. Don't know if you are aware of it or not. I don't say that in a derogatory tone or sarcastic tone- it's just the feedback I would give you - in order to improve your performance in the future. I'm assuming you know your subject but can't communicate it clearly. You've got 25 somewhat extensive posts on this thread/subject matter and it's my feeling that no one (at least myself) has made any progress in understanding your perspective or the context and importance of your point. Every new post doesn't get you any closer to the answer than the previous post.

My only guess to the problem is that the foundation of concepts that supports your viewpoint - that seems obvious to you is not obvious to your audience (me). When you build a concept, idea, system, theory- you can't get to the theory and take everything as self-evident- especially for teaching or describing it's functioning- you've got to essentially retrace the original route - in principle- not point by point- to it's basis- starting reference points- those things that you can see, touch, smell, hear. Homer had a similar problem- so you've got company. You've also got to understand when you mention any particular point- how other people might mis-interpret it and explain and what the wrong turns could be at any turn- so that you keep the reader on track.

So that's why very few people stuck it out with Homer- and very few will stick it out with you- (like me)- so when you ask "This is where the man on scales in lift will help if you need more detail." I'm thinking no thanks- because that post is going to be like the last 25 - not going to get me any closer to you answering and me understanding whatever you were talking about when this thread started.

That's just my feedback- hope it helps you.

[golf_sceptic]

Thanks Mike, I take your comments in the generous spirit in which you sent them.

You've got 25 somewhat extensive posts on this thread/subject matter and it's my feeling that no one (at least myself) has made any progress in understanding your perspective or the context and importance of your point.

Ok. Here's the gist of it. I'm interested in the physics underlying TGM. In essential terms my proposition is that centrifugal force does not cause the throw out effect.

This requires a very precise discussion of the physics. The discussion is not for everybody, requires either training or an inquiring mind and great patience, will only generate fresh insights for the very few, and will interest even fewer.

Now. ThinkingPlus has two physics degrees I believe, and physics is her job. Me too, except that I am now retired and I focussed on Pure and Applied Mathematics in my undergraduate days. Unfortunately, when she took me to task about frames of reference, it takes the discussion to a whole new level of abstraction. I had hoped not to have that discussion, but yoda made it necessary and stephanie put it centre stage.

ThinkingPlus, by the way, has given me an insight into why Mr Kelley may (I emphasize may) have explained centrifugal force in the way he did.

keep the reader on track

Quite right. We all know that my proposition is that centrifugal force does not cause the throw out effect. We've done the boy and the rock to illustrate what is really happening in a simple situation involving centrifugal force (and taken a few side trips). Unless ThinkingPlus wants to discuss physics in non-inertial frames of reference, or anybody else wants to clarify any other issues, I'm ready to state my case.

[12 piece bucket]

I'm not sure that Mr. K ever said that CF had anything to do with "throw-out" did he? The way throw-out was demonstrated to me was that once the clubshaft passes vertical to the ground it falls lengthening the Primary Lever Assembly (left arm and club).

I think people think that throw out is OUT TO THE PLANE LINE . . . but that ain't how it was demonstrated to me.

I think there is a alot of misunderstanding in this thread.

Mike O is mediating debates . . . . what the hell is going on? I'm headin' for the bomb shelter . . . see y'all after the nuclear winter.

[Mike O]

Isn't the Colonel being sued for unhealthy food- I rest my case Mr. Bucket- back to your sofa!!

Golf Sceptic- I actually thought the whole thread was you stating your case- but yes- please clearly state your case.

Thanks,
Mike O.- "Mediator"

[Mathew]

"This throw out action is termed herein as 'Centrifugal Acceleration' to indicate that Centrifugal Force (Centrifugal Reaction), not muscle, is propelling the Secondary Lever Assembly (the golf club) into Impact. So swingers are totally dependant on their skill at manipulating Centrifugal Force while Hitters are not."

What this is saying is that the right shoulder is turning an axis to spin a flywheel - the right shoulder going downplane to make the secondary lever assembly stay onplane via the effect of centrifugal reaction so that it stays at 90 degrees to the turning axis hence it stays onplane. This is what causes the throw out action and whilst pp3 aims to a point to control the clubhead as the release motions whirl it out via the passive straightening of the right arm in conjunction with its trigger delay against the checkrein of the left arm and the delivery line. The structure of the left flying wedge keeps the first imperative of a flat left wrist per law of the flail 2-K whilst all this happens.

This is paragraph is especially skillful to avoid the debate. If centrifugal force or reaction is fictious or not - that will be (or should be) the dictionary definition... which takes nothing away from the effect or correctness of the wording.

Providing this happens



It proves the concept...

[Yoda]

We all know that my proposition is that centrifugal force does not cause the throw out effect. [Bold by Yoda.]

Right you are, golf_sceptic!

Indeed...

Centrifugal force -- induced by rotation -- IS the throw-out effect.

Per Homer Kelley:

"Centrifugal Force: The effort of the Swinging Clubhead to pull the Primary Lever Assembly (Left Arm and Club) into a straight line."

[golf_sceptic]

Thanks yoda. To understand that definition I'd like to pick up on something you said about the stone on the string which I think will probably be best answered by thinkingplus.

Thinkingplus, what yoda says makes sense in a rotating frame of reference. How many of the TGM concepts should be viewed in a non-inertial frame. I think for example of the hinging concepts. Clearly (I hope) any discussion of forces relating to hinging concepts is taking place in a non-inertial frame. What about the concepts of lag and accumulators in respect of a swinger (pardon any mangling of the terminology)? Is that all in a non-inertial frame as well?

Mike, for me, the answer to this question from thinkingplus would put the TGM concepts into an entirely different light so I'll delay putting my proposition pending a response from her. Her response may also lead to a highly technical discussion within a discussion, so hold tight if it gets nerdy.

Mathew, thanks for raising this again. The issue I'm addressing isn't whether centrifugal force is real or ficticious, or how to produce or utilize it in the swing (which your post does really well), but rather that the physics changes depending on the frame of reference, and what yoda and I wrote about whether the centrigual force acts on the stone or the boy are not contradictory at all, but rather merely reflect different frames of reference. This issue may also be the reason why neither of us understood the other earlier on.

[Rumbler]

Thanks yoda. To understand that definition I'd like to pick up on something you said about the stone on the string which I think will probably be best answered by thinkingplus.

Now that's funny!!!!