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# Transitions: An (im)Balancing Act - Page 11

Quote:
Originally Posted by Jamt

I am serious. There is a term centrifugal force, but centrifugal force is apparent, i.e. it does not exist in reality. If you use it in the wrong way as it has been used here it brings no value.

The ground reaction force can be split in different components, one of which is the centripetal force. This is the real force making us turn, but it pushes on the skis, only indirectly on the CoM.

Ah the ugly duckling/black sheep etc.  raises it head.  Believe it or not there are many physics professionals that still disagree on this.

Here is a link that supports Jamt's (and my) position.

Here is one that puts a more rational spin on it.

http://science.howstuffworks.com/centrifugal-force-info.htm

And if you are wondering how and why centripetal force is the driver of our turns, take a look that this.  The Balloon represents the surface of the snow pushing against the ski and the penny represents a bent and edged ski.

Quote:
Originally Posted by epic

Whenever I've been with the best ski instructors, instruction was clear and simple. That's what I strive for. I have no idea what is going on here.
Hehe...no one is ski instructing here. It's a discussion of concepts.

Maybe we'll end up soon resolving the concepts of vaulting and the use of the term centrifugal force. (Breath holding should be avoided on this)
Both(?!) seem to me to relate to why one isn't doing one legged squats with full body weight or more as some seem to think must happen in ILE.
Jamt, what would be nice is to get your physics students to diagram these things.
Question:
In the Mikaela clip, is the cause of the vaulting the tightening of the radius at the gate?
Right, no centrifugal force, move right along, nothing to see here.
Quote:
Originally Posted by Rick

It's really pretty basic.

And yet you make the wrong conclusions. The physics discussion I made was because you stated:

Quote:
Originally Posted by Rick

First, in the transition we are discussing there is no vaulting over the old outside (downhill) ski going on.  You vault over the ski that you're standing on, and there is no weight on the downhill ski.

It should be clear by now that vaulting has to happen. Pretty Basic?

you got the cause and effect mixed up,

there is nothing pushing the skier into the ground, it is a force pushing the skier up.

There is nothing pulling the skier into the next turn, there is a force turning the skier.

Quote:
Originally Posted by rod9301

Right, no centrifugal force, move right along, nothing to see here.

Might seem like a detail but I cannot tell you how many times I have seen people that believe that there is a force pulling you towards the outside of the turn and that when you unload you go in the direction of that force. If you remove the force, centripetal that is, you just keep moving straight forward.

Quote:
Originally Posted by markojp

And Rick, no, you can't call a force anything you want. When you do it becomes fiction.

Yes, pointless friction, resulting from the tired old debates over whether or not centrifugal force is a real force.  We've been over this so many times here at Epic, well before your arrival, Marko, jamt's too.  It's such a "been there, done that" topic to me, a royal waste of time that does nothing but confuse the readers who are actually trying to learn something.  People use the term pervasively in the world of ski instruction, myself and Ron LeMaster to name just a couple, and everyone understands the concept it speaks to.  That's all that matters.

Quote:
Originally Posted by Rick

Yes, pointless friction, resulting from the tired old debates over whether or not centrifugal force is a real force.  We've been over this so many times here at Epic, well before your arrival, Marko, jamt's too.  It's such a "been there, done that" topic to me, a royal waste of time that does nothing but confuse the readers who are actually trying to learn something.  People use the term pervasively in the world of ski instruction, myself and Ron LeMaster to name just a couple, and everyone understands the concept it speaks to.  That's all that matters.

Everyone thinks they understand

Well ok then. I'll defer to senority. Rick, you're tendencies toward 'authority' is what makes discussion challenging.
Quote:
Originally Posted by Jamt

Quote:
Originally Posted by rod9301

Right, no centrifugal force, move right along, nothing to see here.

Might seem like a detail but I cannot tell you how many times I have seen people that believe that there is a force pulling you towards the outside of the turn and that when you unload you go in the direction of that force. If you remove the force, centripetal that is, you just keep moving straight forward.

Yes, but.....

So if you release the centripetal force coming from the snow, at any point say below the fall line, you will move tangent to the curve you were on. As long as that curve isn't across the hill, you will move downhill into the "next turn". Yes? -Well in the area towards the center of the next turn. Had you not released. But now you're in that center area so everything shifts over....and on and on. (I may play with that. I can't say I use it like that since one is usually still on the wrong side of the skis to turn the other way.)

Also, look at the definition posted on howstuffworks.com posted by JESINSTR:

Quote:
Centrifugal Force, in physics, the tendency of an object following a curved path to fly away from the center of curvature. Centrifugal force is not a true force; it is a form of inertia (the tendency of objects that are moving in a straight line to continue moving in a straight line). Centrifugal force is referred to as a force for convenience—because it balances centripetal force, which is a true force

First sentence is what most people remember.

To bring this back to the topic.

The vaulting in Mikaela's first turn in the clip occurs because of the decrease in radius at the gate, yes? Why is this force of vaulting "over" (finished, completed) by 14 seconds on the tape? Wouldn't the body still have inertia from that force?

Originally Posted by Tog
....
In the Mikaela clip, is the cause of the vaulting the tightening of the radius at the gate?

I asked this same question in post 280.  I'd like to hear some responses as would Tog.  Here are the images again:

Here's the turn you folks are talking about.

Here she is, after the gate.

Notice the forward tilt of the torso, and how far forward her left shoulder is compared to her left knee.

The torso is a bit more upright than it was before.

Her left shoulder has moved back slightly compared to the previous frame..

Skis are higher on edge, a wee bit, from that added angulation.

The higher edges of those skis will be sharpening the turn now.

The hips are now rising.

Is that happening because of the skis sharpening the turn under her, or because she is lengthening her left leg?

Both are happening simultaneously.

Lf, those pics are way beyond the tightening of radius at the gate. According to Jamt, the vaulting is over by those pics you posted.

LF, between the first and second pic, she is angulating a little bit more in the second.  When you watch this in motion you can see her lean towards the outside ski, that is the main movement that happens between :12 and :13.  That, combined with holding onto edge engagement, creates the trigger that is vaulting her across.  Her left leg doesn't make any appreciable extension until well after that.  Notice also there is still significant snow spray on the outside ski, the big release of that ski, which would correspond with applying pressure on the left one, is later.  Extending your leg to expand along with the vaulting is entirely different then pushing on it to move your CoM.

Quote:
Originally Posted by Rick

Yes, pointless friction, resulting from the tired old debates over whether or not centrifugal force is a real force.  We've been over this so many times here at Epic, well before your arrival, Marko, jamt's too.  It's such a "been there, done that" topic to me, a royal waste of time that does nothing but confuse the readers who are actually trying to learn something.  People use the term pervasively in the world of ski instruction, myself and Ron LeMaster to name just a couple, and everyone understands the concept it speaks to.  That's all that matters.

Hey Rick JamT.  Here's a thought.  Could it be that with Centrifugal force we have a classic Frame of Reference issue?  We watch (from afar) the video of the 8 ball in a circle and see that indeed the ball exits the circle for an inertial path. That's the physics. But...when I am in a turn and I feel the centrifugal force it doesn't FEEL at all like I am going to release to an inertial path . Instead it FEELS like I will slide out and away down the hill especially as I approach the fall line.

Which brings me to make a comment regarding the recreational environment in which I teach. (podium please)  When you have a majority of the skiing public developing and reinforcing their skiing movements by reacting to Centrifugal force instead of building centripetal force, by fearing death on every turn, and by those that constantly emphasize the outside ski,  it is no wonder they can't break through to higher levels of skiing.   EPIC  is that simple enough?

Originally Posted by Tog

Lf, those pics are way beyond the tightening of radius at the gate. According to Jamt, the vaulting is over by those pics you posted.

Tog, the frames I captured are from just after the gate.

Here's what led up to those three images I posted, plus those three again.

Between 5 and 6 below she uprights her torso, angulating to the outside of the turn.

That's the extra angulation I'm referring to.  I am thinking it immediately tightens the turn.

This is after the gate, as she readies for the next turn.

At frame 3 her edge angles flatten a little, but then as she angulates that little bit they get higher by frame 5.

Do you not see it that way?

Edited by LiquidFeet - 12/10/14 at 1:31pm
Quote:
Originally Posted by JESINSTR

Hey Rick JamT.  Here's a thought.  Could it be that with Centrifugal force we have a classic Frame of Reference issue?  We watch (from afar) the video of the 8 ball in a circle and see that indeed the ball exits the circle for an inertial path. That's the physics. But...when I am in a turn and I feel the centrifugal force it doesn't FEEL at all like I am going to release to an inertial path . Instead it FEELS like I will slide out and away down the hill especially as I approach the fall line.

Which brings me to make a comment regarding the recreational environment in which I teach. (podium please)  When you have a majority of the skiing public developing and reinforcing their skiing movements by reacting to Centrifugal force instead of building centripetal force, by fearing death on every turn, and by those that constantly emphasize the outside ski,  it is no wonder they can't break through to higher levels of skiing.   EPIC  is that simple enough?

I prefer to talk about reactionary forces because that is the thing we are able to manipulate and control directly with our edges which creates turn forces to begin with.  That is where we convert inertia into turning and we use reactionary forces to do it.  Learning to FEEL those forces, harness them, that pressure, we develop our sense of touch around pressure....pressure is reactionary force.  That is what we feel, that is what we respond to, that is what we create through steering angle and edge angle manipulation.  During most turn operations we are trying to create and optimize those forces, or bleed them for the sake of speed controlled peanut butter spreading, etc.

When we release in order to transition, do we suddenly stop creating reactionary forces?  I don't think so, rather we find a way to manipulate our body so that the CoM is not held back by the body stack from letting inertia take it on that straightline tangental path.  Some like to call that centrifugal force, which is not really what it is.  Prior to a release, we have our body positioned in a way so that the reactionary forces coming back from the snow push the feet, which push the legs, which pushes the hip and basically pushes the CoM on a curved path.  Change our body stance so that the legs don't quite push the CoM on that curved path, and the CoM will continue on that straight line tangent to the curve.

Everything we do in release phase of transition is simply about liberating the CoM to follow that straight line.

Its unneccessary to use that kind of language about centrifugal force for this purpose, particularly since its not a real force.  However, learning to feel and manipulate the reactionary forces under our feet is not only real but critically important all throughout a ski turn, so discussing centripetal or reactionary forces makes a lot of sense.  Put your weight on the outside ski why?  So that it will react!

Edited by borntoski683 - 12/10/14 at 1:18pm
Quote:
Originally Posted by Tog

Lf, those pics are way beyond the tightening of radius at the gate. According to Jamt, the vaulting is over by those pics you posted.

What Rick referred to was the two last pictures from LFs sequence. Those are not the ones. The vaulting is over when the outside ski looses pressure.

Quote:
Originally Posted by Tog

The vaulting in Mikaela's first turn in the clip occurs because of the decrease in radius at the gate, yes? Why is this force of vaulting "over" (finished, completed) by 14 seconds on the tape? Wouldn't the body still have inertia from that force?

Yes, tightening, angulation, inside ski pressure, changing angle between centripetal force and slope all play together to vault.

Yes the body will still have inertia, the body will continue to rotate, but since it is not vaulting over the outside leg anymore I wouldn´t call it vaulting.

Regarding the centrifugal force. Have you ever seen a person trying hammer throw for the first time? a lot of those people will let go in the direction of the force and thus throw the hammer 90 degrees in the wrong direction. The "feel" of the force is not always natural. If you know some elemental physics you know when to let go.

Here's what Jamt had to say Lf. He's saying the vaulting was started between 6-7 secs on tape. Got to go or i'd look at your time stamps on the frames.
Quote:
Originally Posted by Jamt

I agree with Tog about the balance. If you are in balance the forces align and the CoM is not accelerating up or down. You could also call that park and ride. In a good turn the CoM is almost always accelerating up or down.

Regarding Mikaelas transition this is the way I see it.

at 6 seconds she has very high edge angles, quite a lot of outside ski bias and a lot of angulation.
at 7 there is a small ridge. The angulation and inside ski pressure starts to accelerate the CoM upwards. Already here the transition to the next turn is started. It is driven primarly by vaulting over the outside leg.
8-9 CoM continues upwards but the acceleration and pressure is disrupted a bit by terrain.
10-11 The pressure comes back with a vengeance due to the previously loss of pressure. less inside ski pressure (relatively speaking), perhaps partly terrain and perhaps partly because she is not extending.
13 both skis  pressured, moving a bit more aft in order to develop lateral inclination in the next turn.
14 the transition is already powered, retracting outside in order to not over-power. inside is retracted slightly after.

The lateral vaulting over the outside is easier to see in the second turn

Jamt, Vaulting is over while the skier is still inclined, and while her CM is still rising because the leg is still vaulting her up?  Not following your line of thinking.

Quote:
Originally Posted by JESINSTR

Hey Rick JamT.  Here's a thought.  Could it be that with Centrifugal force we have a classic Frame of Reference issue?  We watch (from afar) the video of the 8 ball in a circle and see that indeed the ball exits the circle for an inertial path. That's the physics. But...when I am in a turn and I feel the centrifugal force it doesn't FEEL at all like I am going to release to an inertial path . Instead it FEELS like I will slide out and away down the hill especially as I approach the fall line.

It's worth a consideration.  When it comes to centrifugal force, I think my experience is not that people are so much intimidated by it, that it might chuck them out of the turn.  The bigger fear I encounter is  that they haven't yet learned to trust it to keep them in lateral balance when they move their Center of Mass inside their feet while making high speed, sharp turns.  So they don't venture to carve on higher edge angles.  They instead keep their CM above their skis, ride low edge angles, and do skiddy turns to keep their speed down.

Which brings me to make a comment regarding the recreational environment in which I teach. (podium please)  When you have a majority of the skiing public developing and reinforcing their skiing movements by reacting to Centrifugal force instead of building centripetal force, by fearing death on every turn, and by those that constantly emphasize the outside ski,  it is no wonder they can't break through to higher levels of skiing.   EPIC  is that simple enough?

Tell me more about your perspective on overemphasizing the outside ski, would you, JES?

LF, there's so much going on in this particular turn, it's really hard to look at small changes in edge angle and angulation at the moments in time you've focused on to determine what's going on with the transition.  It's that increase in pitch, right as she goes past the gate, that throws things all caddywhompus.  It's easier for me to just look at the video in motion, because what's actually happening jumps right out at me.

As she goes by the gate the hill drops off, she momentarily loses her grip on the snow, and her skis skip sideways.  Her getting taller there is just her effort to quickly reach out with her outside foot and reengage the snow.   Her movements there are not about starting a transition, it's about getting back into the current turn as quickly as she can.  Next, she gets a grip on the snow again, and for a very brief moment continues with her current turn.  Then  just as quickly she uses ILE to initiate the transition and finish the turn.  At the point she started ILE, around 13 seconds, it was like starting the transition from scratch.  All the extra curricular stuff prior to that as she was negotiating the drop off by the gate was a separate event to how the transition was actually executed.

So if you drive a car, with a parcel on the passenger seat, and you take a sharp turn to the left, the package slides to the right. That's becauseoff the centrifugal force.
Same thing happens when you ski, and you hit ice in a turn, you slide to the outside.
Where do you guys get the pseudo physics?
Quote:
Originally Posted by Rick

It's worth a consideration.  When it comes to centrifugal force, I think my experience is not that people are so much intimidated by it, that it might chuck them out of the turn.  The bigger fear I encounter is  that they haven't yet learned to trust it to keep them in lateral balance when they move their Center of Mass inside their feet while making high speed, sharp turns.  So they don't venture to carve on higher edge angles.  They instead keep their CM above their skis, ride low edge angles, and do skiddy turns to keep their speed down.

Tell me more about your perspective on overemphasizing the outside ski, would you, JES?

Rick,

Quote:
Originally Posted by rod9301

So if you drive a car, with a parcel on the passenger seat, and you take a sharp turn to the left, the package slides to the right. That's becauseoff the centrifugal force.
Same thing happens when you ski, and you hit ice in a turn, you slide to the outside.
Where do you guys get the pseudo physics?

Great question!!

So if your watch from a different frame of reference ie from outside the car, you will see that the package travels in a straight (inertial) direction and it is the car that turns into the package. Whereas  you, the driver see the package being slammed against the door which is not what really happened.

This is not sure to inertia. Inertia would be if the driver slams on the brakes, and the package slides forward.
actually, this is ridiculous, I don't even know where to start explaining, and I have a phd in physics.
Quote:
Originally Posted by rod9301

So if you drive a car, with a parcel on the passenger seat, and you take a sharp turn to the left, the package slides to the right. That's becauseoff the centrifugal force.
Same thing happens when you ski, and you hit ice in a turn, you slide to the outside.
Where do you guys get the pseudo physics?

Technically as stated above, the inertia of the package makes it want to continue in a straight line which appears to throw it outward from your point of view. There is not force - the car just turns out from under it basically, until it hits the door. That's why people say it's not a real force - nothing has changed for the package until it gets to the door.

At that point, the door actually exerts a force on the package keeping it turning; That would be a real force. But it's useful for people to think of there being a force pressing the package outward, because it's closer to our experiential frame of reference. So when you're spinning, your senses tell you there's an outward force. A lot of physics calculations will just tell you there's a pushing force inward against you that turns you - not an actual force pulling you outward. The force you seem to feel outward is the force of trying to go in straight line and being turned (by the ground against skis, car door against a package, person on an amusement park ride, etc.)

Quote:
Originally Posted by jc-ski

How about some MA on this?

Hey, sorry JC.  I threw this out there for the others to comment on first, but instead we got sidetracked on the centrifugal force thing.  I'll have a go at it for you.

Between 8 - 13 seconds he comes around the turn at a massively high edge angle, using his outstretched inside hand as a rudder.  That effectively widens his lateral base of support to over 6 feet.  The hand becomes part of what is providing balance, which is why he can ski so inclined and not fall onto his side.

Around 13 seconds he begins to tip his torso back upright, aided by a bit of push with his outstretched left hand he's pulling back towards his body.  At the same time (13 sec) he tips his old outside (right) knee down a bit closer to the snow, which increased his edge angle just a tad.

The cumulative effect of the torso tip, the hand push, counter steering from the knee drop, and the changing forces in Bob Barnes "do nothing" concept, causes him to become laterally out of balance, which causes his body to begin toppling across his skis and into the new turn.

Simultaneously with the toppling, he relaxes his old outside leg to get it out of the way, and extends the old inside leg, so he can get it pressured and engaged as quickly as possible for the new turn.  You can see, just before he's gotten back to edge angle neutral during the roll of edge process, he's already completely on his old inside ski, with the old outside (downhill) ski up off the snow.  He'll now roll onto his downhill edge, with that old inside ski in total charge of the initiation of the new turn.

A lot going on in this one, hard to label it as one particular type of transition.  How much of it do you think was thought out, step by step, as I've described it here?  Not much at all, I'd say.  It's the body genius of an amazing athlete who's doing  on the fly what's he's done countless times before.  We mere mortals have to put a bit more thought into it, learning by isolating and focusing on one thing at a time, before they can even start to gel like this into a cohesive meld of a montage of movement.

Quote:
Originally Posted by JESINSTR

Rick,

Yes, JES?

This is painful.

Centrifugal force exists and is helpful to the analysis IF YOUR FRAME OF REFERENCE IS ACCELERATING, E.G. MOVING ALONG THE CURVE OF THE TURN THE SKIER IS ABOUT TO TRANSITION OUT OF.  That is the view most of us have as we are skiing around a turn.

However in the interests of brevity, and sanity, please, let's stick to an analysis of these transitions with the skier moving in a FRAME OF REFERENCED FIRMLY FIXED TO THE MOUNTAIN the skier is skiing down; we are watching the videos from a stationary camera, not a helmet mounted go pro.

Surely it is easier for those of us who comprehend centrifugal force to use the fixed camera reference system.

Carry on.

Quote:
Originally Posted by Ghost

This is painful.

Centrifugal force exists and is helpful to the analysis IF YOUR FRAME OF REFERENCE IS ACCELERATING, E.G. MOVING ALONG THE CURVE OF THE TURN THE SKIER IS ABOUT TO TRANSITION OUT OF.  That is the view most of us have as we are skiing around a turn.

However in the interests of brevity, and sanity, please, let's stick to an analysis of these transitions with the skier moving in a FRAME OF REFERENCED FIRMLY FIXED TO THE MOUNTAIN the skier is skiing down; we are watching the videos from a stationary camera, not a helmet mounted go pro.

Surely it is easier for those of us who comprehend centrifugal force to use the fixed camera reference system.

Carry on.

Then ask the student who's looking to actually apply this to their skiing to simply reverse their frame of reference from everything we've said.

See why I said earlier this here subject is a very slippery slope, and tried to avoid it like the plague?

Painful, indeed, maybe stick to skiing, instead of trying to deny centrifugal force.

Any idea why these machines are called centrifuges?

Probably not designed by ski instructors.
Quote:
Originally Posted by rod9301

This is not sure to inertia. Inertia would be if the driver slams on the brakes, and the package slides forward.
actually, this is ridiculous, I don't even know where to start explaining, and I have a phd in physics.
Well! So now we have you and Jamt with phd's in physics. It appears you have a diff of opinion but im sure it could be worked out I think it would be best to start a new thread on centrifigal force and skiing. This comes up over and over.

Jamt, if the outside foot has no pressure in the Mikaela sequence why wouldnt the vaulting continue with the inside foot as fulcrum?
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