They call it weight shift....

[JeffM]

Golfbulldog

Unfortunately, I don't have the expertise to define the term effective mass as it applies to the golf swing, but I can envisage what it refers to in simplistic conceptual terms.

Consider the clubhead in the mid downswing. It is travelling down an inclined arc towards the ground at a certain speed at any specific time-point in the mid-downswing. The clubhead has a finite mass, but the force of its movement in the direction of the ground is obviously affected by its speed of movement, and its effective mass (relative to the ground) is a combination of its finite mass and the speed vector that is directed in the direction of the ground. Its effective mass essentially determines the magnitude of the force that would be needed to change its path direction. I think that the same principle applies to torso movements in the downswing. When Tiger Woods starts the downswing, he uses torso muscular forces to push his torso down towards the ground and also left-laterally. That added muscular force causes the effective mass of the moving torso to be different to the static COG mass at any time-point in the downswing, because the body is always moving throughout the downswing and the body movement has a force vector that is directed both to the left and groundwards. I don't know how to calculate the magnitude of this force, but I can perceive its presence when I swing a golf club. When I am approaching impact, my torso (which has a certain degree of secondary axis tilt) is well behind the center of the stance, but there is no doubt in my mind that the force over the left foot (directed groundwards) far exceeds the force over the right foot. I can therefore easily understand Hogan's assertion that 85% of the effective mass is over the left foot as one nears impact.

Jeff.

 

[birdie_man]

Would you like to ATTEMPT an EXPLANATION?

That is horrible USEage of CAPS.

You clearly are a rookie in the art my friend.



EDITED FOR SPELLING.

 

[mandrin]

I reckon that most great players are actually very centred at impact...COG is centred between their stance....

If you lift either leg they will fall - all that means is that the COG is not over the foot which remains on the ground... Clearly Hogan's COG is not 85% towards his left foot....

But he , and many others describe a weight/feel shift...Do they feel this actually when they swing or do they only "feel" it when they see photos of their right foot up on tip toes and assume that their weight must be predominantly on their left foot??

Who knows...

golfbulldog,

The issue of weight shifting in a golf swing is an interesting but rather fuzzy affair.

We are aware of a ‘weight shift’ primarily by sensing the pressure between feet and ground. However, simply momentarily lifting one foot will immediately put all the weight on the other foot yet there has been no lateral shift of any body part. Hence our senses can be very misleading.

Shifting/rotating slowly body, arms or club will lead to a quasi-static transfer of weight. Doing the same very quickly can lead to quite a different dynamic weight shift. During a down swing our weight can actually both exceed and become less than our static weight.

 

[golfbulldog]

Thanks Mandrin , I had forgotten the previous thread which extended to 14 pages.... not surprising as it went slightly off thread several times and you nearly caused Birdieman Cranium explosion if you remember!!

But I think your http://www.angelfire.com/realm/moetown/mandrin/golf/Weight_Shift_1.html

,with the little robot nearly toppling over, helps me.

I think it points out the science that Jeffman has been suggesting.

If we replace our little robot with little boy like http://www.youtube.com/watch?v=oLZ7ZbxAcvo

He experiences these forces and does not fall over... He looks like he is "making the club work like a club"...

There is obviously something in the little boy's brain ( which is not in Little Robot) that recognises the forces and makes a corrective motion to stop him falling over...

In fact, the club works like it should because he did not fall over...

So can you use the parts of the brain which stop us falling over to make the club work like it should??

Interestingly I find myself arguing towrds Puttmad's opinion which he expressed in the 14 page thread (page 4) as :-

"OK. My final word on weight shift.
Weight shift is the body's attempt to remain in balance when various bodily components (in this case the hands and arms) are being moved outside the natural center of balance...
In other words , weight shift is something done as a reaction, not an action, therefore is a complimentary action...

Weight shift should support the intent of the hands (to apply maximum force to the ball) and therefore must be integrated as a supporting part of that process, without overdoing or exaggerating its role..."


To which Brian replied " I totally disagree!" ... maybe we keep this thread tight...7 pages max!!

 

[speedracer68]

There is one pro with a weight shift machine and it shows how your weight usually stays centered during the swing and it transfers to the inside of the left foot in the end..I don't think i can use his name here but that weight machine seems dead on..

Also i remember brian telling us that the swing is like standing on both sides of a crate..shift too much on one side and the other side will hit you on the shin..=)

 

[puttmad]

...

There is one pro with a weight shift machine and it shows how your weight usually stays centered during the swing and it transfers to the inside of the left foot in the end..I don't think i can use his name here but that weight machine seems dead on..

Bobby Shaeffer would agree with you on that one....
He found that at the "pre-impact" positon, when the clubshaft is parallel to the ground, he had the same amount of weight on both feet...
Now it may not have felt that way, but that was the reality...
At impact the weight was moving foreward...

 

[mandrin]

Thanks Mandrin , I had forgotten the previous thread which extended to 14 pages.... not surprising as it went slightly off thread several times and you nearly caused Birdieman Cranium explosion if you remember!!

But I think your http://www.angelfire.com/realm/moetown/mandrin/golf/Weight_Shift_1.html

,with the little robot nearly toppling over, helps me.

I think it points out the science that Jeffman has been suggesting.

If we replace our little robot with little boy like http://www.youtube.com/watch?v=oLZ7ZbxAcvo

He experiences these forces and does not fall over... He looks like he is "making the club work like a club"...

There is obviously something in the little boy's brain ( which is not in Little Robot) that recognises the forces and makes a corrective motion to stop him falling over...

In fact, the club works like it should because he did not fall over...

So can you use the parts of the brain which stop us falling over to make the club work like it should??

Interestingly I find myself arguing towrds Puttmad's opinion which he expressed in the 14 page thread (page 4) as :-

"OK. My final word on weight shift.
Weight shift is the body's attempt to remain in balance when various bodily components (in this case the hands and arms) are being moved outside the natural center of balance...
In other words , weight shift is something done as a reaction, not an action, therefore is a complimentary action...

Weight shift should support the intent of the hands (to apply maximum force to the ball) and therefore must be integrated as a supporting part of that process, without overdoing or exaggerating its role..."


To which Brian replied " I totally disagree!" ... maybe we keep this thread tight...7 pages max!!

golfbulldog,

There is a substantial difference between our senses and reality regarding weight shift. Moreover I wonder if weight shift is actualy generally understood in such way hat people readily agree on this issue. However this makes it an ideal subject of discussion for golf forums.

During the downswing Tiger shifts his body vertically - downwards and upwards. Moreover he also shifts his weight horizontally accompanying all this with a vigorous rotation around both a vertical and a horizontal axis.

There are hence various ways to use the body. However an optimum swing likely includes motion of the heavy body parts, as cause not effect, to obtain adequate velocity for the clubhead with the least amount of strain/effort on all parts involved thus favoring also accuracy, repeatability and longevity.