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Author Topic: the centre - mechanical and mythical...  (Read 3605 times)
elisedance
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ee


« on: June 07, 2009, 04:19:59 AM »

I think we need a separate topic on this.  The mythical centre - we hear about it all the time 'move your centre' (hey, down south you move your center, its the same thing Wink). 

Your gravitational centre is within your body, somewhere in your abdomen (this can be demonstrated by suspending a stiff body from a single attachment point and adjusting it to different angles - the point that does not move is its centre of gravity) .  However, the centre of gravity is not a static thing - if you extend a limb your gravitational centre shifts

However, in dance terms the centre is often regarded as a static entity - I'm not quite sure in which position the body has to be in so that the dance centre is the same as the gravitational centre - presumably standing in dance position - and the dance centre is slightly different depending on the dance itself - perhaps someone can help me here but I guess that a ballet dancer's centre is not precisely the same as a standard or a latin dancer's.

The real reason I want to start this thread is because I suspect that 'the dance centre' is not at the gravitational centre at all - but lets get to that a bit later.  I am sure there are different interpretations to this concept than what I wrote above - and I hope others here can help define this mythical beast  Wink
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Dora-Satya Veda
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« Reply #1 on: June 07, 2009, 11:51:28 AM »

I was always taught there are many different centers used in Ballroom dancing.

Just to mention a few

Center of Gravity, Center of Weight, Center of Connection, Center of Balance, Center of Rotation, Center of Turn, Center of Swing, Center of Self, Center of Partner, Center of Movement, Dead Center, The Active Centers, The Static Centers and The Shaping Center

Now this is just some of them. It is just the ones that I remember it this very moment…

Most of the time I think teachers will shorten the sentence and just refer to “center” not explaining which center they are actually talking about.

All my teachers talked about “the center”. In the beginning I actually didn’t even understand that I didn’t understand. I thought as all my teachers used the same word, they must all mean the same thing. It soon became very apparent that I had no clue what they were talking about. So for a while this subject was really confusing and very illusive to me. I would go into a lesson and the teacher talked about “the center” but it was not necessarily the same center that was talked about throughout the lesson. My main teacher started going over each of the centers and with time a clear understand and picture started to form. Little by little I started understanding what center the teacher/s was/were talking about in reference to the action requested and the explanation they gave.

The “center” understanding is a very biiiigggg subject.

Sorry to put more wood on the fire…….or confuse you all even more.


Dora-Satya Veda
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elisedance
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ee


« Reply #2 on: June 07, 2009, 01:59:46 PM »

Not at all - I knew it was a fire, I just didn't know it was quite that biiig Smiley

I'm also rather pleased that this confusion has also happened to me  - but in my case its not due to different teachers (to be honest, most I have dealt with are not nearly that sophisticated) but to a departure of centre (of gravity) from centre of what I guess is balance from your list above - which is what I think is the most 'common' centre discussed.  If you talk about moving your centre I think most people interpret this the same way - a static place in your middle around which things move.  As discussed above, that place is close to but not exactly your centre of gravity - because your centre is conceived as being on one place whereas your centre of gravity changes as you move any part of your body unless you have an equal weight shift in the opposite direction - which would effectively stop you from moving Wink

A 'personal centre' (for want of a better term - I'm not sure how to translate that to your list above, if it can be) is, I think, a very useful concept for partner dancing - its in essence 'where your partner is' .  But centers that we use personally for dancing are different and starting that idea needs a new post.... 
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elisedance
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ee


« Reply #3 on: June 07, 2009, 02:04:23 PM »

So, the real reason for this topic.  I used to 'dance my centre', or try to.  Move my body as one across the floor and let my limbs achieve that.  Hopefully that is quite a good description of walking, a frequent analogy on this forum.  However, recently we have been working on the base, basically the hips down sabilizing this so that I dance grounded and permitting my upper body to do its thing - which is most of all to be ralxed Wink 

This has made me aware of two centres for dancing: one roughly between my hips (lower than my centre of gravity) and the other one higher up - but I have not actually discovered precisely where yet Smiley

I now have a grounded centre - is this at all related to the centre of balance that you referred to above DSV? 
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pruthe
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« Reply #4 on: June 10, 2009, 09:36:42 AM »

There's an interesting graphic on center of gravity at following location.

http://www.answers.com/topic/center-of-gravity

Scroll down to "Sports Science and Medicine" section. Here graphic shows how center of gravity can move depending upon body position. When in dance position with arms up, the center of gravity moves higher than when arms are down. I'm thinking this point (extended to right side of body) might be the optimal point to make a connection with your partner. Also you would want to make sure you're standing straight with blocks of weight (head, shoulders, rib cage, hips) on top of each other down through center of foot. This could provide the optimal position to initiate movement. You would probably want to keep center at same point in body even as body and legs are moving. Now if we redraw the graphic showing dance partners facing each other and (lightly) connected at this contact point, there may be another center of gravity for the combined body masses. You'd probably want to always keep this combined center of gravity at the same point between partners. Does this make sense? I'm still thinking on how all this works and what one is trying to achieve in balance between dance partners.
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pruthe
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« Reply #5 on: June 10, 2009, 01:10:11 PM »

BTW, I was re-reading EE and DSV's posts on this subject and I guess at this point, I'm trying to understand the center of gravity concept first and how it possibly relates to ballroom dance. Obviously, I'm not at a point of discussing any other kinds of centers, for example, the "dance center" that EE alluded to, or the "center of balance" that DSV alluded to. Maybe that and other centers will become clearer in future discussions. (Or maybe I need to book a lesson with DSV the next time she comes around to get the full story.  Grin )
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"It's not what you do, but how you do it."

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elisedance
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ee


« Reply #6 on: June 10, 2009, 03:10:31 PM »

..or you can make up your own centre-type and join the gurus Smiley
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pruthe
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« Reply #7 on: June 10, 2009, 04:35:10 PM »

Grin
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"It's not what you do, but how you do it."

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TangoDancer
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« Reply #8 on: June 11, 2009, 12:58:30 AM »

WHAT A GREAT TOPIC !!!!

DSV is most accurate; I, too, have been drilled in, I think it was 20 different centers (I'll try to list them if necessary). If I understand ED correctly, what she is looking for are the 2 stationary (some persons say primary) centers...gravitational and postural.

Your take on the gravitational center is correct, though we could discuss it further. For the other, let's begin at Pruthe's post and link to the Sports Medicine thingy. It shows gravitational center (the dot), but not postural. Here is where we learn about one's CPA. No, not one's accountant.    Roll Eyes  CPA - corrective Posture Arc. Stand straight as with your back against a wall, and the weight over the heels (like in the sports Med diagram). Very slowly move the body forward from the ankles caring not to bend at the waist, until it has reached a position over the arches of the feet. You will feel leaned forward and off balance b/c you are not accustomed to it. However, keeping the heels on the floor, and feeling the line under the feetwhere the front of the arch meets the back of the ball, you will feel ultimately lighter. This lightness is b/c it is here that the body is perfectly balanced over the feet.

The arc between straight up over the heels and straight up over the insteps is one's CPA, and where one should stand, walk, dance. This is also one's postural center.
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skipper
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« Reply #9 on: June 14, 2009, 09:12:05 PM »

The EXACT center or centers is in  a different place for each person. I always think about "energy balls". They are about the size of walnuts. And they move my body in the direction that my partner asks me to go.
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cornutt
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« Reply #10 on: June 14, 2009, 09:45:46 PM »

IYour gravitational centre is within your body, somewhere in your abdomen (this can be demonstrated by suspending a stiff body from a single attachment point and adjusting it to different angles - the point that does not move is its centre of gravity) .  However, the centre of gravity is not a static thing - if you extend a limb your gravitational centre shifts
[...]
The real reason I want to start this thread is because I suspect that 'the dance centre' is not at the gravitational centre at all - but lets get to that a bit later.  I am sure there are different interpretations to this concept than what I wrote above - and I hope others here can help define this mythical beast  Wink

I just did an experiment... I balanced myself on the top edge of the back of the couch.  The line of balance turned out to be just above the top of my pelvic bone, which is a few inches lower than I thought it would be.  I tried it with my arms straight down at my sides, and with my arms crossed at the top of my chest (closer to where you'd hold them in a dance frame), and it made very little difference.

So yes, that CG is quite a bit lower than where most instructors teach you that your dance center is.  I think that's because the concept of the dance center isn't really based on that kind of static balance -- it has more to do with the complex of muscles in your abdomen, which are involved in coordinating the motions of nearly every part of your body, except for your arms.  Most dance instructors that I've talked to about it teach that the dance center is somewhere between your diaphragm and your belly button. 
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MusicChica
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« Reply #11 on: June 14, 2009, 10:08:23 PM »

I just did an experiment... I balanced myself on the top edge of the back of the couch.

Please tell me DW got a picture of this. Cheesy
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cornutt
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« Reply #12 on: June 14, 2009, 10:13:36 PM »

No, I did this with the old couch downstairs.  She would have killed me if she had caught me doing this on the good couch!   Wink
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Vagabond
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« Reply #13 on: June 14, 2009, 10:35:54 PM »

There is a more scientific way to obtain your centre of gravity.

With the use of the masses of body segments it can be calculated. What you need to know is the total height and weight of a person. One of frequently used methods was described by Zatsiorskji and Selujanov (1979), who determined the parameters B0, B1 a B2 for each body segment.

The equation for body mass is as follow;
mi=Bo+B1m+B2v
where m (kg) is total mass of a person  and  v (in cm!) is height of a person..

The parameters B0 , B1 a B2;


Table of weight segments coefficients.
   
Segment nameB0(kg)B1B2(kg/cm)
Head+neck1,2960,01710,0143
Hand-0,11650,00360,00175
Forearm0,31850,01445-0,00114
Upperarm0,250,03012-0,0027
Leg-0,8290,00770,0073
Shank-1,5920,036160,0121
Thigh-2,6490,14630,0137
Trunk   
Upper part of the trunk8,21440,1862-0,0584
Middle part of the trunk7,1810,2234-0,0663
Lower part of the trunk-7,4980,09760,04896


Centre of gravity (c.g.) of body segments was determined experimentally.


Hand (manus) 39:61 %, forearm 43:57 %, upperarm 44:56 %, head+neck 50:50 %, trunk 42:58% (from shoulder), thigh 43:57%, shank 41:59 %, foot 40:60 % of total lenght of each segment (from proximal end).

If you want to define total centre of gravity of a person, you must know:

    * the mass of each body segments
    * the x,  y and z coordinate  of centre of gravity of each body segment

But from this we can roughly calculate each occurrence of C.G. with angles and limbs sticking out

The centre of gravity of human body varies for example according to sex /size;
females = larger pelvis => c.g. lower than males,
baby = larger head in comparison to other parts of body =>c.g. higher than juveniles teenagers or adults
« Last Edit: June 15, 2009, 08:35:12 AM by Vagabond » Logged

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elisedance
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ee


« Reply #14 on: June 15, 2009, 06:04:31 AM »

awesome V - I think I understood the last three lines anyway Smiley
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