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Physics of a Step
Posted by sqq
10/29/2006  8:38:00 AM
There are pictures of some walking phases on the site www.racewalk.com (/TECHNIQUE/Basic Technique).

Imagine on the pictures a vertical vector line drawn from the balance point of the body down on the floor.

If the line is in front of or behind the supporting point of the foot on the floor you are statically imbalanced and some horizontal dynamic force is needed on the height of the balance point of the body to push you for or backwards to maintain balance of the moments(m x g = m x a x h) and keep the mowing foot off the floor. The dynamic force is horizontally towards the balance point of the body on the side of the moving foot and must be produced by acceleration or deceleration and inertia of the body. Pushing of the supporting foot speeds up and landing on the supporting foot slows down the velocity of the body. Speeding up velocity is accelerating and slowing down velocity is decelerating.

Balance is static only at the instants the balance point of the body is exactly above the supporting point of the foot on the floor or between the two feet both supporting an equal weight which can be almost weightless. Race walkers should always have a foot on the grund but on mid-stride tend to have feet weightless off the grund.

Upward deceleration and downward acceleration do reduce the weight of a body.

Dance steps are different but obey the same laws of physics.

Dancing lady too should take care of her horizontal accelerations to carry her own weight.

Walkers and dancers instinctively control movements by forces produced by accelerations and inertia but it can be useful sometimes to learn, understand, think and concentrate to feel the forces. Google: mass inertia acceleration force
Re: Physics of a Step
Posted by Anonymous
10/29/2006  8:54:00 AM
Very good points SQQ, though perhaps to mathematical for everyone to follow.

"If the line is in front of or behind the supporting point of the foot on the floor you are statically imbalanced

Balance is static only at the instants the balance point of the body is exactly above the supporting point of the foot on the floor or between the two feet"

Yes, this is the technical definition of imbalance. However, dancers tend to emotionally use the word only for situations in which they feel undesired movement. I've had complements of how I never put someone off balance throughout a challenging amaglamation - yet the fact is, I did. What I didn't do was impose any destabalizing forces or force their weight to move off their foot in innapopriate ways - we were off balance a lot of the time, but only in the ways necessary to move. There was nothing alarming.

"Race walkers should always have a foot on the grund but on mid-stride tend to have feet weightless off the grund."

And fully flighted dancers may tend at mid-stride to have both feet weightless, but either on the ground or so close to it that you can't tell they aren't.

"Walkers and dancers instinctively control movements by forces produced by accelerations and inertia but it can be useful sometimes to learn, understand, think and concentrate to feel the forces."

Most healthy adults ordinary down the street walk is actually an oustdancing dance action (though there are occasional exceptions). It makes perfect use of imbalance at the right point in the action. The problem is that two things tend to spoil this naturally perfect action.

The first is putting a partner in their path - people try to avoid stepping on the partner, thus breaking the natural continuity of their action in a way that actually increases the chances of stepping on their partner. If they just walked forward naturally, their partner would simply walk backward naturally.

The second problem is with lowering to move forward. Preserving the same natural weight progress would mean that the weight is moving during the lowering - and indeed, advanced dancers do it this way. The problem is that if you try to send your body weight forward while lowering, you can easily end up stumbling forward. Stumbling is not good, so your teacher will make you learn to lower with your weight in place over your foot. But that is only an introductory idea. To really dance, you must learn to send your weight forward, and when it is past your foot embrace the faling movement this creates. But to make it not a stumble, you have to keep your body vertical as you do it. stumbling would have your shoulders getting ahead of your hips - whears an aligned dance action would have them moving at the same speed, or maybe even the hips a tiny bit ahead of the shoulders (and that tiny bit may feel like a lot!)

And of course the backwards partner can't just charge off into movement - they have to establish connection first, so there's merit into compressing forwards towards the partner and against the movement briefly early in the lowering, before moving in the real direction together. But that compression is only a brief phase - if you compress forward throughout the lowering, you have not initiated a backwards step at all, instead simply droped the partnership into an awkward and comparatively immoblized limb tangle.
Re: Physics of a Step
Posted by Anonymous
10/29/2006  9:15:00 AM
That racewalk site is indeed quite interesting.

The major difference from dancing seems to be their rule that the arriving leg must remain straight with an unflexed knee until the body is over the foot. In dancing, we would only do that to lead a heel turn, otherwise we would soften into the knee. And of course they have to lift a foot actually off the road to move it, wheras we can slide an unweighted foot across a dance floor.

But many other things are similar. Notice that they also get most of the stride behind the body with less leg swing ahead of the body, even though there is no partner for a forward reaching leg to hit. And see the warning on how trying to overstride and pull yourself onto the front heel is ineffiicient.
Re: Physics of a Step
Posted by Anon 3
10/29/2006  8:05:00 PM
Sqq. Does the article say a foot clear of the floor. Where we differ as a dancer is that the ball and then the heel is in contact with the floor. Not a heavy contact, but still a contact. Heavy contact which we have on the back foot. and light on the front foot will not allow our weight to be too far forward at the mid -point, from there it will increase untill there is full weight. The rear foot will start heavy and like the front foot will alter. Our friend Anonymous will have his weight too far forward too soon .
Heavy on the front and light on the back.Thus will produce a body position that is too far forward. Hence the imbalanced position of the weight which he seems to think should happen.
I haven't yet read the article you pointed out. But I will. Thanks.
Re: Physics of a Step
Posted by Anonymous
10/29/2006  8:33:00 PM
"I haven't yet read the article you pointed out."

Next time you might want to read it before posting with no idea what you are talking about...

"Heavy on the front and light on the back.Thus will produce a body position that is too far forward."

Not "heavy" on either foot exactly. But definitely the body is closer to the front foot. The race walkers (who would not tolerate an efficiency unless it is required by their rulebook) have figured out it's best to do it that why. Meanwhile leading ballrom dancers have also long been doing it that way, for both efficiency and because there just happens to be another body in front of you, limiting how far ahead of you your legs can swing...

Kind of nice that the needs of efficieny and partnering turn out not to conflict in this case, isn't it?

Hence the imbalanced position of the weight which he seems to think should happen.
I haven't yet read the article you pointed out. But I will. Thanks.
Re: Physics of a Step
Posted by Anon 3
10/29/2006  9:55:00 PM
Anonymous Weight closer to the front foot only after reaching Midway ( split weight ).
Vertical . If the line is in front or behind you are off balance and not vertical. Yes or No. No smoke screens please.
As we start with feet together the weight is on the LF. Our knee will flex and we will start to start to move. The knee is in front. At the completion of the step the whole thing will be repeated. The only difference is the rear foot will be retained which we don't have the luxury of unless we take a prep step. At no time are we away from verticl.
Re: Physics of a Step
Posted by Anonymous
10/30/2006  6:38:00 AM
"Anonymous Weight closer to the front foot only after reaching Midway ( split weight )."

No, weight closer to the front foot from the time it passes the standing foot onwards. Remember that until you put weight on the receiving foot, your body will be off balance - and the further your moving foot is ahead of your body, the more severely your body will be off balance.

"Vertical . If the line is in front or behind you are off balance and not vertical. Yes or No. No smoke screens please."

I am absolutely vertical from the knees up. A line from my shoulder will drop through my hip which will drop through my standing knee. This is vertical. However, there comes a time in the action when this line will touch the floor in front of the standing toe. At this point, my body is still perfectly aligned vertically, but it is no longer balanced on the standing foot - in plain fact, it is falling.

You can also do this without bending the knee, with the body vertical from the hip up through the shoulder. And that is something that you - Mr. or Mrs. Anon3, have been doing in every ordinary non-dance walk since you were two years old - haven't you. You simply have not yet figured out who to maintain the same alignment while moving forward from knee lowering, for purposes of dancing.

"As we start with feet together the weight is on the LF. Our knee will flex and we will start to start to move. The knee is in front."

The standing left knee is in front of the standing foot, yes. And the hip, center, and shoulder are vertically aligned over that knee, which means they are forward of the standing foot, too.

"At no time are we away from verticl."

Exactly. What you haven't yet realized is that being off balance is compatible with this - in fact, it is required to achieve this.

Are you still REFUSING TO LOOK at the picture in learning center, forward walk, 2, extension?
Re: Physics of a Step
Posted by Anon 3.
10/30/2006  3:47:00 PM
Anonymous. What exactly do you find wrong in picture two. The body is verticl. The front leg is moving on a heel. The back heel hasn't yet left the floor, but it will as the front foot is pushed to its full extension. At which point the balance is mid- way between the two feet as in picture three. Picture four . The front heel is on the floor. The back foot is to the toe. From there we go to picture one. This is just as it is in the technique book. At no time has the body got in front of the moving leg. Just for the record if you look at picture one on the Backward Walk you will see where the lady feet should be on the count of (and)That is three and.
Not like the man who will commence from a position where the feet are closer. For the lady I always say you've given yourself a flying start. With feet together you are liable to be pushed onto your first step.
I find nothing wrong here at all. On picture four if that were John Wood or any top dancer the rear knee will be much closer to the ground, the front leg will corrispond to the back. It is a good idea if picture three on the Forward Walks is studied. Most of us instead of two straightish legs at this point.Most of us are already bent. Anonymous , This is your weak point.That is why your weight is too far forward to the point of no return.
I find the pictures Forward and Backward exellent.
For those who are new to this. Go to the Learning Centre on this site and then Forward Walk. Look and learn. Look in particular to the rear foot on pictures two to three. This is why I suggest that to have a hand, on a table, to keep steady and simulate all from one to four slowly.
I wish you all good luck and hope you succeed, which you will. Just remember there is no such thing as can't. There is only I have not yet learnt.
Re: Physics of a Step
Posted by Anonymous
10/30/2006  6:55:00 PM
"Anonymous. What exactly do you find wrong in picture two. The body is vertical."

Actually, if you are talking about 2:extension in the learning center, that was something I've been trying to call your attention to for weeks - because it shows an important and necessary element which you so far haven't been able to understand.

As you note, the body is nicely vertical. However, if you drop a line from the shoulder through the hip and through the knee, that line will fall forward of the toe of the standing foot. Pretty plane proof that the body pictured there cannot possibly be in balance over the rear or standing foot. Which is exactly as it should be.

"The front leg is moving on a heel."

That's what is wrong with the picture - the front leg has swung too far for the progress that the body has made into the step. Of course the front foot will eventually develop onto a heel, but it shouldn't be there yet. With this much bend in the knee, a large step is clearly being attempted, which means that the body should have moved more before the free leg got that far in advance of the body.

And having that free leg so far out in front will mean the body is not apporpiately off balance, but is unreasonably and unstainably off balance. Such a position with an over-reached free foot as illustrated is probably only sustainable by sliding part of the weight on the moving foot as it moves. So that part of the picture is wrong.

But the position of the body and the standing leg is a good illustration of something that should be happening - if only the moving leg had not yet moved so far, it would be great.

"This is just as it is in the technique book."

Sort of - the details are there, but the proportions are all wrong.

"At no time has the body got in front of the moving leg."

That's the problem with the image sequence. However if you erase the moving leg from image number two, that particular slide does show something that should be happening. The rest of it is mis-sequenced - even our adminstrator has said he'd like to do it over someday.
Re: Physics of a Step
Posted by Anon3
10/30/2006  11:49:00 PM
I don't think the pictures are that bad. Fom position one the RF is holding its ground . In two that knee is flexing and the left is moving. Just as it was put to me once. It is like the jaws of a vice which one side was static and the other being moved. I doubt if anybody would get too much of a bad idea from this. If you go to the Backward Walk and start at three through to one. How is two there..
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