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# A simple self-assessment test - Page 14

Quote:

Originally Posted by Ghost

and there is nothing stopping us from looking at it that way with the skier in about an 8 m radius turn, considering his mass at his CoM and the axis about 7 m away from him) the skier is doing 4 times the rotational speed, but since the radius is only half as much, each rotation only takes him half as far across the snow, so he is really covering twice as much distance per second.  Really the numbers were chosen to make the mass easier, in reality, he would be able to move his mass about 1/2 a meter, but it illustrates the effect, and at those distances and typical speeds his angular velocity and momentum are small. The angular momentum is quite small, compared to the linear momentum, except perhaps after a collisions that makes him spin. ; we will be arguing about gyroscopic effects next , and then Coriolis, but hey, let's account for every dyne and erg.

Its somewhat interesting to talk about angular velocity there, but angular momentum has a requirement that is not being met for all practical purposes.

My understanding about momentum is that momentum is a state of mass and velocity that if not acted upon by other forces, will continue in the same motion until something acts on it to change it.

Angular momentum is created or destroyed with torque.  You spin a top and it spins without any other force until friction eventually stops it or you apply some reverse torque to slow it down.  The angular velocity could change if you can change the moment of inertia, but momentum is preserved.

A skier traveling on a curved path does not posses any angular momentum as some are presenting.  If nothing else acts on the skier, he will travel in a straight line, not a round circumference.  There is not any angular momentum present.  Continual external forces are causing it to travel on a curved path.  A skier does not have angular momentum UNLESS he gets some torque introduced that will cause him to start spinning this way or that.  Here are some examples of angular momentum in skiing:

• You hit a bump, your weight is too far forward.  This causes a torque against the front of your feet which causes your body to rotate forward into a face slam
• You catch an edge going very fast which creates torque on your ski and cartwheel down the hill
• You crest a bump and your weight is too far back, gravity grabs your skis and pulls them down the hill, i.e., torque and your body spins backwards in angular momentum until you fall on your butt
• You take a jump and do various ariels in the air, with lots of angular momentum going on.
•  etc...

The turn shape does not qualify for angular momentum.

That being said Ghost, in real terms the question is, is a skier making a turn; experiencing any rotational momentum within their body alone (not the greater turn radius).  I think that is what you are suggesting.  its possible there is a very tiny little bit, but not very much.  The muscle actions that we do when we rotate or counter rotate our upper body easily out trump any angular momentum that exists within us alone as single body.

Quote:
Originally Posted by borntoski683

...

Please describe what you mean by "transition" in that statement.  What I can say about skate parks is that you are going around using ramps and half pipes and playing with gravity that is coming from the U side of the half pipe...that is what makes it possible to do all those things on a swing, in a half pipe, etc..  The conditions on an open ski slope are simply not the same.

...

If you don't know what trannie is in that statement, or how ski slopes have elements of transition in them, then you really shouldn't be commenting from an assumed position of authority in this portion of the thread, at all.

oh here comes the credibility police again.  I was asking what he meant.

BTS...I don't know. The more I think about it----CT actually helped transform my slalom skiing last season. For instance, did you know that tech racers ROUTINELY  lift their inside ski in transition?? Would never have known  As soon as I found that out I was easily 3 seconds faster! We may do well to pay heed to him here...

zenny

Edited by zentune - 9/6/13 at 7:54pm
Quote:
Originally Posted by Ghost

About that negative work.  It's all positive as fare as our muscles are concerned, but it can be negative or possitive to the system; if the force and the velocity are in opposite directions, the product of force and displacement is negative and so it decreases the kinetic energy of the skier, we call that negative work.  It's just a convention.

Yep I understand about the greater system and the mathematical reason for using a negative number.  That is exactly what has led some of these guys to a false understanding.

In practical matters in terms of skiing, you still have to create the force that will create this idea of negative work, related to kinetic energy.  The false premises being presented are that this negative work will come by just flexing to remove pressure....and it doesn't come that way.  You can remove pressure to zero.  Zero work.  Then the work that has a negative in the equation has to come from somewhere....and extreme flexing does not bring it.   Positive forces in an opposite direction must contribute to create the mathematical negative work.  It won't come from our body as a negative.  Positives in the opposite direction have to create a mathematical negative.

Quote:
Originally Posted by borntoski683

very good up to the point about lowering your mass to dump speed.

Again, I can't prove this with physics, just the reality of proving it in person. It happens, daily, just ask any boarder/skater. You can only argue this not to be true, until you experience it in person.

Please describe what you mean by "transition" in that statement.  What I can say about skate parks is that you are going around using ramps and half pipes and playing with gravity that is coming from the U side of the half pipe...that is what makes it possible to do all those things on a swing, in a half pipe, etc..  The conditions on an open ski slope are simply not the same.

A transition is a place where the slope changes; either a ramp, pipe, bowl, hip or mogul. Generally you pump as the grade changes to gain speed (momentum). It is a very real technique and usually used to get to the top of a slope, or around a bowl, when your speed alone is insufficient. You can also pump on the flats, as has been shown with edits earlier in this thread.

Just depends what you mean by transition in skiing.  If you're talking about the edge change then flexing to release will not slow you at all.  There is no angular momentum there, you have linear momentum and its conserved.

In skiing, a transition is any place there is a change in the slope, like the face of a mogul or a hip. This is where people pump to get air. You may never have done it, but skiers frequently dump speed on the moguls by collapsing their frame to help recovery after a mistake, you can see them slow as they crouch. This is dumping speed by "anti pumping".

Skateboards to skates to skis to snowboards.......concrete to snow......skate parks to ski resorts........transitions are transitions and the reality doesn't change.

Quote:
Originally Posted by MrGolfAnalogy

Quote:
Originally Posted by borntoski683

very good up to the point about lowering your mass to dump speed.

Again, I can't prove this with physics, just the reality of proving it in person. It happens, daily, just ask any boarder/skater. You can only argue this not to be true, until you experience it in person.

This was in reply to your statement about a hurdle jumper which is a bit different than a ramp or half pipe.  They are jumping over hurdles...  as you said, by clearing the hurdle they are not slowed down.  That is absorbing.  GOOD.  then you implied that a hurdle jumper would slow down by lowering their CoM.  No they would not slow down unless they hit the hurdle, creating pressure and deceleration.  Actually the lower they can go while clearing the hurdle, the faster their time will be because shorter path to travel.

Quote:
Originally Posted by MrGolfAnalogy

Quote:
Originally Posted by borntoski683

Please describe what you mean by "transition" in that statement.  What I can say about skate parks is that you are going around using ramps and half pipes and playing with gravity that is coming from the U side of the half pipe...that is what makes it possible to do all those things on a swing, in a half pipe, etc..  The conditions on an open ski slope are simply not the same.

A transition is a place where the slope changes; either a ramp, pipe, bowl, hip or mogul. Generally you pump as the grade changes to gain speed (momentum). It is a very real technique and usually used to get to the top of a slope, or around a bowl, when your speed alone is insufficient. You can also pump on the flats, as has been shown with edits earlier in this thread.

ok got it.   I was not sure if you were relating to ski turn transitions.  But 3D terrain feature transitions, ok got it.

As has been said by me and others already numerous times, no argument about 3D features enabling you to create pressures that can speed you up or slow you down, depending on the direction of the pressures you embrace and all relative to the direction of gravity.   Pumping on the flats will only work if you are swiveling in order to create a possibility to push laterally in a way that will provide propulsion, but yes, nobody has argued that point.  Why do you guys keep bringing it up?

Quote:
Originally Posted by MrGolfAnalogy

Quote:
Originally Posted by borntoski683

Just depends what you mean by transition in skiing.  If you're talking about the edge change then flexing to release will not slow you at all.  There is no angular momentum there, you have linear momentum and its conserved.

In skiing, a transition is any place there is a change in the slope, like the face of a mogul or a hip. This is where people pump to get air. You may never have done it, but skiers frequently dump speed on the moguls by collapsing their frame to help recovery after a mistake, you can see them slow as they crouch. This is dumping speed by "anti pumping".

And here is the crux of the matter.  The misunderstanding...the dreaded anti-pump.  The false physics.

Collapsing their frame does not slow them down.  Just like you said above about the hurdle jumper, absorbing keeps them going faster.  If they make a mistake most likely they are plowing into the face of the next bump.  The pressures created from plowing into that is slowing them.  They may collapse to reduce the impact of plowing into the bump, ie absorb it, but if there is slowing down its because of the extra pressure created as they plow into it, or because they do some speed checking with their edges somehow.

Round and round we go...where it stops, nobody knows....

Quote:
Originally Posted by borntoski683

Round and round we go...where it stops, nobody knows....

The physics argument will never stop it, but actually experiencing it will. Just go to your local skate park and ask a boarder to compress into a transition to slow down. You'll see.

The effect is almost similar to dropping from a height onto your feet and using your legs to absorb to force and slow yourself down. In this case to "floor" becomes the up slope of the mogul, which you are effectively falling into with your forward speed. The angle isn't ninety degrees but the effect is the same.

And yes, the hurdler was only meant to be an example of momentum preservation by keeping to center mass level regardless of the terrain beneath it.

Quote:
Originally Posted by MrGolfAnalogy

The effect is almost similar to dropping from a height onto your feet and using your legs to absorb to force and slow yourself down. In this case to "floor" becomes the up slope of the mogul, which you are effectively falling into with your forward speed. The angle isn't ninety degrees but the effect is the same.

when you you jump off a roof or high place and land on flat ground, as you have now presented, you are stopped by pressure against the ground, which creates upward acceleration.  If you don't absorb, you will stop no matter what.  Your speed will be stopped.  Its only a question of how gradually you will be stopped.  Flexing makes it more gradual and easier on your body by spreading the pressure out over time.  Not flexing will probably result in injury, but you will be stopped just the same, but the same total net pressure or upward force to decelerate you back to zero.

You are not anti-pumping your falling velocity to zero.

Quote:
Originally Posted by MrGolfAnalogy

The physics argument will never stop it, but actually experiencing it will. Just go to your local skate park and ask a boarder to compress into a transition to slow down. You'll see.

I don't have to ride in a skate park to know you are doing it.  I know you are, but not for the reasons you believe it to be.  It doesn't really matter in the park, if that's the frame of mind you're in and its working for you then great...but when you start translating false physics into ski technique, problems arise.  You don't slow down by lowering you CoM, that is nonsense.

How about a weight in an old fashioned centrifugal governor on an engine, or a ball on a string.   They can be analyzed as rotatinal motion.  The tension in the arms/string is the same as the centripetal force of the skis on the snow.  You are over-thinking this.

If you integrate the forces as you go over bumps and rollers down the slope (integrate over time), and you chose to apply more pressure on the back sides of bumps than the uphill sides helping you along, the integral of F*d is positive you go faster.  If you apply more on the uphill sides slowing you down, you will go slower.  Timing is everything.

Also, more tail pressure, less tip pressure to speed up; more tip pressure, less tail pressure to slow down.

No I don't think I'm over thinking it.  I think angular mechanics are being used falsely without thinking it through, and bad ski technique is being derived from that false notion.

so let's take the case of ball on a string.  That is not angular momentum because the axel is not rotating.  The ball is swinging around it and the only reason it is swinging around it is because of the external force coming from the fixed in place axel, through tension on the string.  Cut the string and the ball goes straight.  You can measure angular velocity yes, but there is no angular momentum present, only linear momentum that is being constantly redirected into a circle.  If the axel became detached from what it was attached to, the angular motion would cease, like a slingshot the entire mass would move linearly in some tangent direction.

Conversely,

If you have a ball attached to a rod that is attached to an axel, such that the axel is not attached to anything else and is also rotating around along with the rod and ball...they are a solid and inflexible mass and somehow angular momentum is established such that the entire mass is spinning that way....not very likely due to the weight imbalance, but hypothetically...that would be angular momentum.

There are some reasons for using angular mechanics and equations while analzying the way a ball rotates around a string, for example, but nonetheless you cannot say that this system really has angular momentum because external forces are required to maintain it.

Without actual angular momentum, then you can do equations all day long, but there is no moment of inertia to manipulate as some have suggested on this thread.  See what I mean?

Edited by borntoski683 - 9/6/13 at 9:46pm
Quote:
Originally Posted by Ghost

If you integrate the forces as you go over bumps and rollers down the slope (integrate over time), and you chose to apply more pressure on the back sides of bumps than the uphill sides helping you along, the integral of F*d is positive you go faster.  If you apply more on the uphill sides slowing you down, you will go slower.  Timing is everything.

Also, more tail pressure, less tip pressure to speed up; more tip pressure, less tail pressure to slow down.

These points absolutely...!

also Ghost, I am really curious about the math here and you're the man to figure it out....

but if you have a given object with mass M at radius R with angular velocity X, and then you change the radius to R2 such that it doubles the angular velocity to Y.  The question is, what is the actual velocity of the object along the circumference in both cases?

Why do I have a feeling its close to the same, if not the very same?

Quote:
Originally Posted by borntoski683

I don't have to ride in a skate park to know you are doing it.  I know you are, but not for the reasons you believe it to be.  It doesn't really matter in the park, if that's the frame of mind you're in and its working for you then great...but when you start translating false physics into ski technique, problems arise.  You don't slow down by lowering you CoM, that is nonsense.

All that matters is the practical example of the application, theoretical arguments not withstanding.

Edited to avoid duplication in the next post.

Edited by MrGolfAnalogy - 9/6/13 at 11:56pm
Quote:
Originally Posted by borntoski683

when you you jump off a roof or high place and land on flat ground, as you have now presented, you are stopped by pressure against the ground, which creates upward acceleration.  If you don't absorb, you will stop no matter what.  Your speed will be stopped.  Its only a question of how gradually you will be stopped.  Flexing makes it more gradual and easier on your body by spreading the pressure out over time.  Not flexing will probably result in injury, but you will be stopped just the same, but the same total net pressure or upward force to decelerate you back to zero.

You are not anti-pumping your falling velocity to zero.

Again, I'm sorry, but you have missed the entire point of the example. We are not bricks that fall without influence, we are capable of creating change, with our legs. It is not relevant that we will eventually hit the ground, it is relevant that we can use our legs to alter our rate of fall. In the example we use our legs to decelerate. Just like you can in a skate park or a bump field, same technique.

You are tying yourself in knots making this far more complicated than it is and trying to prove us all wrong . Why?

You're almost there MGA.  There is absolutely nothing complicated about this, and you're the one that brought it up.  Don't give up.  If you alter your rate of fall, how do you do that?  You push against the ground.  If your body is falling with X amount of momentum it has to be decelerated by enough amount to stop all that momentum.  There is no other way to swim up through the air to decelerate yourself.  You have to push against something.  When you land on the ground there is action/reaction against the ground and you will stop.  If you flex at the same time as taking that extra pressure, you spread that slow down over time so that the pressure is spread over time into manageable impulses.  That is simply how it works.   The upwards pressure from the ground stops you by an exact amount of upwards acceleration, ie, force...ie, pressure, its just a question of how suddenly.  For a bag of bricks its very sudden.  For someone flexing their legs on impact, its taken gradually and less impactfully.

I get that in your mind you are imagining that somehow you can suck up the falling speed, but it doesn't work that way and it doesn't translate into other ski technique that has been proposed.    In a way I understand why you are using a mental image of sucking up the speed, but really what you are doing is sucking up the upward forces, not the speed....and you actually aren't sucking up anything...you're just spreading it out over time so that your body can handle it.

Anyway, I have tried tirelessly to get some of you see this really basic physics, which you seem unwilling to even consider.... and you certainly haven't convinced me (and probably a few others), of your fantasy science either...so maybe we're just going to have to agree to disagree.

peace

Edited by borntoski683 - 9/7/13 at 12:44am
Quote:
Originally Posted by Josh Matta

Quote:
Originally Posted by borntoski683

when you you jump off a roof or high place and land on flat ground, as you have now presented, you are stopped by pressure against the ground, which creates upward acceleration.  If you don't absorb, you will stop no matter what.  Your speed will be stopped.  Its only a question of how gradually you will be stopped.  Flexing makes it more gradual and easier on your body by spreading the pressure out over time.  Not flexing will probably result in injury, but you will be stopped just the same, but the same total net pressure or upward force to decelerate you back to zero.

You are not anti-pumping your falling velocity to zero.

Quote:
Originally Posted by MrGolfAnalogy

Again, I'm sorry, but you have missed the entire point of the example. We are not bricks that fall without influence, we are capable of creating change, with our legs. It is not relevant that we will eventually hit the ground, it is relevant that we can use our legs to alter our rate of fall. In the example we use our legs to decelerate. Just like you can in a skate park or a bump field, same technique.

You are tying yourself in knots making this far more complicated than it is and trying to prove us all wrong . Why?

I can not speak to BTS's motivations however I will express my views of why this forum has posters who are dogmatic about expressing their opinions to the point of ridiculing the opposing ones. Not sure if you ever experience this but I have.... in HS and in college, if you ever say the teacher or prof is wrong and prove it in front of the class, you may get the full ire for the rest of the semester. Most likely, you're not going to get this treatment from the open minded ones b/c they cherish new ideas. Now to bring that scenerio to this forum, most of the posters are ski instructors, they work in an environment where they are in full command of the classroom albeit on the slopes, they are use to saying what is right and what is wrong in their setting. Some may like the setting of dictating what is right versus wrong to the point where they thrive on it while others like helping newbies learn, btw a free ski pass doesn't hurt in any case. Then you work your way up the PSIA ladder for certs, where you have to pass through a chain of gate keepers again they deem what is right and wrong. IMO, the whole process tends to attract and maintain insular people and ideas to the point where they have become dogmatic about there beliefs.

I should apologize to ski instructors in general b/c I have met and skied with some really cool ones but its the close minded ones that have turned me off.

Edited by jack97 - 9/7/13 at 7:26am
Quote:
Originally Posted by jack97

I specifically state "not quite" b/c the movement of the hand is not minor, it is major since this the mass that has moved with respect to the center of rotation. Now if you meant "this is minor" with respect to the vid I posted where the prof show the same experiment b/c it shares the same concept then I would agree with you.

adding energy is minor, changing moment of inertia is major. They are both caused by pulling the hands in.

Quote:
Originally Posted by borntoski683

Nope.

Everything you are talking about is about reducing your muscle output from something positive to zero against other external forces.  Your body can't do negative work.  If you retract to the point that you are no longer resisting anything than you stop contributing to the previous thing, you might start contributing to another thing in the other direction, but its still output only.

Nope, if you fall face down and put your arms out to brace the fall you are reducing your momentum and lessening the impact force on your nose.  If you lean forward and press i.e. hop just before you hit it so you are going down instead of flat or up hitting the transition instead of sucking up a roller you are reducing your momentum and speed using the same principle.

This thread reminds me of the scene from Boogie Nights where Dirk is trying to get the their tapes from the studio owner.

Studio guy.. "give me the money for the recording sessions and I'll give you the tapes"...

Dirk Diggler "give me the tapes and then we can get you the money"...

over and over and over....

Edited by crgildart - 9/7/13 at 7:59am

Surprised there hasn't any reference to the Laws of Thermodynamics in this thread.

Quote:
Originally Posted by zentune

BTS...I don't know. The more I think about it----CT actually helped transform my slalom skiing last season. For instance, did you know that tech racers ROUTINELY  lift their inside ski in transition?? Would never have known  As soon as I found that out I was easily 3 seconds faster! We may do well to pay heed to him here...

zenny

That thread, http://www.epicski.com/t/115477/a-question-about-leg-movements-and-turning/60 , was an interesting one, because it was another where I got blocked without explanation or warning because I was discussing real ski technique that some found...surprising.  (Yes, there were barbs thrown back and forth, but I think even Zentune agrees that he and multiple other posters threw barbs in addition to me.)  It's important for passive readers to understand the vested interests on here, and to realize that the thread they read is often the result of a lot of social pressure, and occasionally very opaquely moderated so that only a certain view may be expressed.  So, points that, in the real world are simply facts of life, such as that lifting of the inside ski, or some of what's been mentioned in this thread, get attacked and treated as something as out-there as if someone were claiming that Tomba had no experience with women.

So, for a passive reader on here, part of that self-assessment should be, do I roll the way real-world players roll?  That's different from trying to conform to a social norm and socially driven notion of skiing and what's possible while skiing as sometimes advanced on here.

Remember how TheRusty noted that he didn't think skidding/drifting was necessarily that advanced, so long as you tried to learn to do it?  Using absorption as one other point of self-assessment, one approach is to say it's impossible.  Another is to learn how to do it.

Quote:
Originally Posted by borntoski683

also Ghost, I am really curious about the math here and you're the man to figure it out....

but if you have a given object with mass M at radius R with angular velocity X, and then you change the radius to R2 such that it doubles the angular velocity to Y.  The question is, what is the actual velocity of the object along the circumference in both cases?

Why do I have a feeling its close to the same, if not the very same?

I did, but I used the "new math" (algebra - really thousands of years old, just reintroduced to the masses in schools in Italy in 1600, and to the US in the 20th century).  Let's put in some hard numbers.

 Conversion factor: 1 rotation (rotations)   =  1 =  1  circumference (m) 1 circumference (m)               1 rotation (rotations) Speed V1= 5 m/s Radius R1= 10 m Circumference C1=2*Pi*R1 62.83185 m Angular Velocity W1= V/C 0.079577 Rotations per second (W=V*conversion factor), radius R2= 5 m circumference C2=2*PI*R2 31.41593 m Mass M1=M2= 70 kg Moment of Inertia I1=M*R1*R1 7000 kg m^2 Moment of Inertia I2= MR2*R1 1750 kg m^2 Angular Momentum L1=I1*W1 557.0423 kg m^2Rotations/s Angular Momentum L2=L1 557.0423 kg m^2Rotations/s angular velocity W2=L2/I2 0.31831 Rotations per second velocity V2=C2*W2 10 m/s Half as far from axis of rotation = twice as fast.

That's why a proper left hook is delivered with the elbow bent to 90 degrees and up close and personal, and can be augmented merging it with an uppercut to liver, but I digress..

You think it's less of an increase, because you figure half as far away, but half the circumference cancel each other out, but I varies as R^2, so it's 2x2/2 = 2 times.

A fun (and dangerous) game to play with a bunch of friends is to all get a merry go round spinning as fast as you can, then all but one converge to the centre of it. Take video ;)

Quote:
Originally Posted by crgildart

Nope, if you fall face down and put your arms out to brace the fall you are reducing your momentum and lessening the impact force on your nose.  If you lean forward and press i.e. hop just before you hit it so you are going down instead of flat or up hitting the transition instead of sucking up a roller you are reducing your momentum and speed using the same principle.

If you fall down and put your arms out to brace the fall, you reduce your momentum with the bracing, you mentioned.

Your description of the 3D transition is not entirely clear to me so I can't comment about it.

Quote:
Originally Posted by Ghost

 Conversion factor: 1 rotation (rotations)   =  1 =  1  circumference (m) 1 circumference (m)               1 rotation (rotations) Speed V1= 5 m/s Radius R1= 10 m Circumference C1=2*Pi*R1 62.83185 m Angular Velocity W1= V/C 0.079577 Rotations per second (W=V*conversion factor), radius R2= 5 m circumference C2=2*PI*R2 31.41593 m Mass M1=M2= 70 kg Moment of Inertia I1=M*R1*R1 7000 kg m^2 Moment of Inertia I2= MR2*R1 1750 kg m^2 Angular Momentum L1=I1*W1 557.0423 kg m^2Rotations/s Angular Momentum L2=L1 557.0423 kg m^2Rotations/s angular velocity W2=L2/I2 0.31831 Rotations per second velocity V2=C2*W2 10 m/s Half as far from axis of rotation = twice as fast.

That's why a proper left hook is delivered with the elbow bent to 90 degrees and up close and personal, and can be augmented merging it with an uppercut to liver, but I digress..

You think it's less of an increase, because you figure half as far away, but half the circumference cancel each other out, but I varies as R^2, so it's 2x2/2 = 2 times.

A fun (and dangerous) game to play with a bunch of friends is to all get a merry go round spinning as fast as you can, then all but one converge to the centre of it. Take video ;)

Tangential velocity?  never mind, that's what you mean by velocity I think.  The example you gave about the merry go round is why when your CoM moves inside, your feet are traveling faster than your CoM

Edited by borntoski683 - 9/7/13 at 9:50am
Quote:
Originally Posted by CTKook

Quote:
Originally Posted by zentune

BTS...I don't know. The more I think about it----CT actually helped transform my slalom skiing last season. For instance, did you know that tech racers ROUTINELY  lift their inside ski in transition?? Would never have known  As soon as I found that out I was easily 3 seconds faster! We may do well to pay heed to him here...

zenny

That thread, http://www.epicski.com/t/115477/a-question-about-leg-movements-and-turning/60 , was an interesting one, because it was another where I got blocked without explanation or warning because I was discussing real ski technique that some found...surprising.  (Yes, there were barbs thrown back and forth, but I think even Zentune agrees that he and multiple other posters threw barbs in addition to me.)  It's important for passive readers to understand the vested interests on here, and to realize that the thread they read is often the result of a lot of social pressure, and occasionally very opaquely moderated so that only a certain view may be expressed.  So, points that, in the real world are simply facts of life, such as that lifting of the inside ski, or some of what's been mentioned in this thread, get attacked and treated as something as out-there as if someone were claiming that Tomba had no experience with women.

So, for a passive reader on here, part of that self-assessment should be, do I roll the way real-world players roll?  That's different from trying to conform to a social norm and socially driven notion of skiing and what's possible while skiing as sometimes advanced on here.

Remember how TheRusty noted that he didn't think skidding/drifting was necessarily that advanced, so long as you tried to learn to do it?  Using absorption as one other point of self-assessment, one approach is to say it's impossible.  Another is to learn how to do it.

It seems to me that nobody is disputing CTKook's ability to ski, just his ability to explain what is going on using Newtonian physics.

I would hazard a guess that both BTS and CTK can ski bumps and absorb speed.  And hawks fly quite well without doing any math.  Physics can be a help or a hindrance to learning.For those who are engineers or mathematicians, it might help them learn, but not if the physics is off.  For others, conceptualizing the physics is irrelevant.

IMHO nobody is disputing the reality of CTKook's skiing.  The reason for the debate IMHO, is not to discredit or maintain image, but a sincere quest for truth.  Surely the explanation and the reality must match for a true explanation.

Let's look at that whole momentum and applied force for a moment.  Read any advanced bump skiing thread on here, and you will likely find Bob B's animation with the "back peddling" move.  As the skis go from crest through the trough, prior to impacting the uphill side of the bump, the skis, feet, and legs are moved forward.  Momentum is being transferred from upper body to the legs.  When the skis contact the bump, even if the skier does not actively resist with his leg muscles during that time, their momentum is being reduced by the impulse as the skis contact the bump.  No active muscle movement required; momentum transfer has effectively been spread out by the initial back peddling move to include the entire time of skiing, smooth and seemingly effortless.  Even if you don't resist at the bump, your legs are loosing momentum, extra momentum that you put into them.  There, now the physics matches the reality.

Quote:
Originally Posted by Ghost

Let's look at that whole momentum and applied force for a moment.  Read any advanced bump skiing thread on here, and you will likely find Bob B's animation with the "back peddling" move.  As the skis go from crest through the trough, prior to impacting the uphill side of the bump, the skis, feet, and legs are moved forward.  Momentum is being transferred from upper body to the legs.  When the skis contact the bump, even if the skier does not actively resist with his leg muscles during that time, their momentum is being reduced by the impulse as the skis contact the bump.  No active muscle movement required; momentum transfer has effectively been spread out by the initial back peddling move to include the entire time of skiing, smooth and seemingly effortless.  Even if you don't resist at the bump, your legs are loosing momentum, extra momentum that you put into them.  There, now the physics matches the reality.

That impulse is pressure resistance.  But you are right its possible to be stacked  at the moment of first hitting the face of the bump so that a large impulse of pressure does not have to involve so much muscle work.  That means most of the speed reduction happens before flexing under that scenario.  Momentum of the CoM is what matters here, back pedaling changes your states of balance, but unless it contributes to resistance and pressure its not changing your momentum.

Ghost?

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