or Connect
New Posts  All Forums:Forum Nav:

Dan Dipiro's Mogul Book - Page 27

Quote:
Originally Posted by Tog

I look at it like this as jamt mentioned in another thread. Hammer flies tangent to curve not directly out.

Reducing pressure is like lengthening the wire on the hammer ball. Or just lengthening your radius. I think. Pressure and standing height might complicate things beyond this?

wtf?  Using the build up of angular velocity and releasing it to achieve an amount of linear velocity or kinetic energy.  Maybe NASA should to this to save fuel when they send out space ships.....

ok, kidding aside. it is pretty hard to figure out how much angular speed is increase or reduce due to external forces. However as a minimum, proper timing of the COM can mean the difference in the skis jetting off the the bump. Here's Fearing's second vid and its better b/c he talks in English. Starting 18:20, he doing that A&E drill on the rollers, in a later sequence he skip/hops over them and you can see the difference in how the COM moves.

The vid has a sequence following the A&E where he gives some pointers about throwing an extra turn by emphasizing that knee roll. Something I have been working on when I hit a mogul field that has flat troughs. When that happens, I can't rely on controlling speed by using absorption for the plain simple fact that the terrain doesn't give me any range to move my COM.

Quote:
Originally Posted by Jamt

I don't see how you can first say that the height has increased with delta and then in the next sentence say that you cannot get any height amplifications.

A better approach to get amplification with a flat bottom would be to double pump. It is not possible without it.

It is gravity that enables pumping and it can be utilized in many ways. Without gravity you would have true conservation (would also need a full pipe)

Another way to look at things is the forces involved. The vertical forces pushing on the rider will determine how high he gets. It should be intuitively obvious that the forces are larger in the case when you extend at the bottom and flex towards the top than if you don't.

I have tried to explain in various ways how it works and I have even calculated an example. The next step would be to build this into a physics simulator, but that just feel like too much work at the moment.

Be my guest to prove that it is not possible. To prove that you need to show that the energy returned by flexing the legs close to the top is exactly equal to mg(delta h)

This is the end.  This is my last post about physics.  Don’t miss it.  I’m sure many of you will give a sigh of relief.  JanT, I hear that you have a Ph.D. in physics.  We’re going to have to get our Ph.D. committees together for a conference, because one of our Ph.D.s should be revoked over this.

If you put energy E into a system and you get out kE, that energy is amplified by a factor of k.  In a passive system, E in, must equal, E out, to satisfy conservation of energy.  For a mass in a gravitational field, height is energy.  If you put in a (delta)h into a passive system you have to get out (delta)h.  If you get out k(delta)h, you’ve amplified, so you must have additional energy injected somewhere into the system.

In the halfpipe example, when you push against gravity you inject mg(delta)h energy.  Your starting energy is mgh so your output energy must be mgh+mg(delta)h.  For a spatially constant conservative gravitational field, it doesn’t matter where you inject that energy.  You can do it at the beginning of the half pipe, at the end of the half pipe, on the flat spot in the middle or anywhere on the flat spot in the middle.  When you move a mass against gravity you inject mg(delta)h energy.

This is by no means a proof, but I googled for 5 seconds and came up with a video below that shows how people approach these problems.  This is how I was taught in my physics classes to approach these problems.  This is how I approach these problems every day to produce innovative devices that tally and convert energy that I sell all over the world.

This concept is so core, that if I’m wrong my whole life is a lie and everything I’ve said is nonsense.  I’m just another clamoring voice of nonsense added to the mix.  What use am I?  It’s futile for me to contribute.  Or, I can’t even convince a Ph.D. in physics (with agreeing voices no less) the most basic physics 101 concept.  What’s the point of being a voice of reason unheard and useless amid unreasonable doubts?  Right or wrong, this shows my uselessness, and I will go back to finding ways to contribute that are more productive.  This wouldn’t be the first time I’ve had to straighten out a Ph.D. in physics and it won’t be the last, but we need to be in person.  This forum is not the place.

Edited by The Engineer - 5/7/15 at 7:37am
Would you care to sum up the last post in a conclusion about the pumping effect?
Quote:
wtf?  Using the build up of angular velocity and releasing it to achieve an amount of linear velocity or kinetic energy.  Maybe NASA should to this to save fuel when they send out space ships.....

well the example was used for what direction do you go when you leave the wall. The question was if there's a component that forces you back into the middle or out of the pipe when you leave the wall.

Quote:
Originally Posted by The Engineer

This is the end.  This is my last post about physics.  ...

Bummer.

On the one hand I am sympathetic, because I understand all too well the frustration of posting glaringly obvious stuff only to have dedicated forum posters insist on an inversion of reality on here, on social grounds.  And there is a real cost to that in terms of keeping posters who you want to post, from posting.

I was rather hoping you would have conceded the point instead, because then I was looking forward to powering my skateboard down a slight incline by doing nothing other than squatting and rising.  This would have been neat, and could even revolutionize ski racing.  We had "skumping" cross over from skating to ski racing as a term (of very minor usefulness) recently, but imagine if racers could increase speed while staying in a tuck just by doing a little up and down butt wiggle.  But, I suppose the revolution will have to wait in that regard.

I've been following this thread on and off...sorry if this had been covered, but has anyone actually posted video of mogul skiers pumping for speed down an entire run? And I don't mean a pump track video with a series of 8 or so rolls, but one of actual honest to goodness moguls, preferably wherein they specifically discuss pumping as a viable technique/tactic? I tried google, but alas, to no avail...

zenny
Quote:
Originally Posted by zentune

I've been following this thread on and off...sorry if this had been covered, but has anyone actually posted video of mogul skiers pumping for speed down an entire run? And I don't mean a pump track video with a series of 8 or so rolls, but one of actual honest to goodness moguls, preferably wherein they specifically discuss pumping as a viable technique/goal?

zenny

No one has ever said bump skiers pump to increase speed in the normal course.

There has been video posted of a ski pump track.

You can also do this on a traverse, and in fact it is common for people to do this on traverses.

Quote:
Originally Posted by zentune

I've been following this thread on and off...sorry if this had been covered, but has anyone actually posted video of mogul skiers pumping for speed down an entire run? And I don't mean a pump track video with a series of 8 or so rolls, but one of actual honest to goodness moguls, preferably wherein they specifically discuss pumping as a viable technique/tactic? I tried google, but alas, to no avail...

zenny

With the incline of most moguls course (Deer Valley ~ 35 degrees) I don't think this is a concern, so that may explain your lack of search results.

But I think the beginning of skier cross events and bicycle cross events over rollers at the start suggests that pumping is what the participants actually do

You guys are making it more complicated than it needs to be.

The swing example is a good one.  Pumping a swing adds energy and makes it go faster.  You can also slow a swing down.  Most of us have done it.  You don't need to have knowledge of the physics involved to know that it works and you can do it.  You can turn it upside down and see opportunities to kill speed in the curve going over the crest as well as the curve going through the troph.  You can turn it sideways and relate to your curves in the horizontal plane.  You can turn it any which way you choose.  The affect and the effect are real (but small- vid infra).

However, consider this.  When you slow the swing down (or speed it up) your legs are doing the work.  Just take a look at how much energy is involved in descending a hill.  The potential energy is enormous.  Conservation of energy gives us mgh at the top = (1/2mv^2 -  losses ) at the bottom.  Any patroller who has ever skated or even walked briskly up a short uphill stretch to an accident patient knows how tiring it can be, so does anyone who has ever hiked for turns.  Simply put, there is no way you could sustain working against that kinetic energy gain (transition from potential energy)  to maintain a constant speed descending any respectable hill by doing the work yourself.   Whatever you can do via, let's call it anti-pumping, is negligible compared to what you have to let friction take care of.

I thought as much...so what's the concern regarding this then? This IS a moguls thread, no??

zenny
Quote:
Originally Posted by zentune

I thought as much...so what's the concern regarding this then? This IS a moguls thread, no??

zenny

????????  Absorption doesn't relate to mogul skiing?  So, bump skiers don't pump for speed, they do absorb.

Or are you just trying to muddy the waters?

This is making the Centrifugal force discussions look simple.

Ghost with the swing i take it you disagree with the physicist that posted on quora? It's up above somewhere.
Ct, I am definitely pro A&E (and Backpedaling as needed), but those are not necessarily the same as pumping. I am trying to clear the waters here.

zenny
I'm happy that TE has satisfied his need to understand why pumping in a half pipe works and how energy is conserved, but that was never a question that anyone contested. Nobody here has said you can't pump in a half pipe or pump track to propel yourself. That has been understood by all from the get go. Jamt said nothing contrary to what TE finally decided to declare triumphantly, that we can pump in a half pipe to add energy.

The question under dispute has always been how to control speed, not how to pump to go faster.

In TE's estimation we push to add energy. Ok. But we can only push once. Under kook's theory when we flex our legs to get ready for another pump the flexing anti-pump should take energy back into our legs and we would have no net gain.

It doesn't work that way, it does matter where in the pipe we pump and where we flex to slow down, so there must be more to the story. its a much more complicated system then that.
Quote:
Originally Posted by zentune

Ct, I am definitely pro A&E (and Backpedaling as needed), but those are not necessarily the same as pumping. I am trying to clear the waters here.

zenny

Tilt that ski pump track.  Yes, he was not going 30mph around it, but he was doing ok.  How steep could it go for him to control speed solely the same way?  Reasonably steep. aka a mellow bumped up blue.

These threads tend to always devolve into people either denying that bump coaches talk about significant (roughly 50/50) speed control coming from absorption, or saying that bump coaches don't know what they're talking about.

Consider that if you can control speed solely through A&E on a mellow blue, that it might still be a very meaningful part of speed control on a steeper run.  Technique-wise, it would be good to learn it, and I guarantee that while the majority of posters here may say they can do it, video would show a different story.

Quote:
Originally Posted by borntoski683

...

In TE's estimation we push to add energy. Ok. But we can only push once. Under kook's theory when we flex our legs to get ready for another pump the flexing anti-pump should take energy back into our legs and we would have no net gain....

Dewdman, this was pretty funny.  But, another blatant misrepresentation.

Please explain how so so we can continue discussing, otherwise it's a useless accusation
And just to be clear, kook nobody is saying that the action commonly referred to as "absorption" or "flexing" is not readily endorsed by everyone. Nobody disputes that we need to actively flex. There is some dispute about the effects of pressure during that endeavor. This is because there is dispute about what flexing accomplishes. You seem to feel that flexing our legs soaks up energy somehow and soaks up speed. Others feel that pressure is essential for the speed control and if we absorb that pressure we reduce the slowing effect. Please correct me if I am misstating your POV
Ct, from my view, "speed" is controlled largely via "turn shape" by managing the cm/bos fore/aft up/down lateral relationship. If I get pushed back at the wrong time, for instance, I am on my tails and out of control in the bumps, aka my feet speed up and I may not recover, so I absorb and extend (and push/pull the feet underneath the cm) appropriately so that I can optimize the cm's flow and remain balanced.

Again, not quite the same as literally slowing down as one can still be hauling much ass while doing so.

zenny
Yep zenny. Another interesting point: the mogul logic video that is often posted where chuck is talking about absorption and speed control, in the same breathe he talks about pulling the feet back. basically preventing the skis from shooting forward on the backside, which would ultimately result in losing control including speed control. So in a sense, this flexing and foot pullback is not only about balance. Also I guess if you pull your feet back you get just a few milliseconds more of pressure on the face of the bump
Quote:
Originally Posted by zentune

Ct, from my view, "speed" is controlled largely via "turn shape" by managing the cm/bos fore/aft up/down lateral relationship. If I get pushed back at the wrong time, for instance, I am on my tails and out of control in the bumps, aka my feet speed up and I may not recover, so I absorb and extend (and push/pull the feet underneath the cm) appropriately so that I can optimize the cm's flow and remain balanced.

Again, not quite the same as literally slowing down as one can still be hauling much ass while doing so.

zenny

That's helpful, you sound more or less similar theoretically to Nailbender, and think that people like Chuck Martin have it wrong.

Which is fine -- there was another thread on here recently where the majority opinion likewise seemed to be that the coaches who produced Shiffrin were advocating a "wrong" drill and harmful movements.  The level of understanding on here often seems to outstrip the highest levels of the sport, and as regards moguls this may be an example.

He he, wrong again ct (I really dig Chuck Martin). BTW, if your going to call out others here regarding their ability to ski the bumps, or anything else for that matter, it would be helpful for you to at least have an avatar depicting you skiing because, for all I know you could be some fat middle aged man living in his mothers basement who hasn't skied a day in his life ;-)

zenny
Quote:
Originally Posted by CTKook

Quote:
Originally Posted by zentune

Ct, from my view, "speed" is controlled largely via "turn shape" by managing the cm/bos fore/aft up/down lateral relationship. If I get pushed back at the wrong time, for instance, I am on my tails and out of control in the bumps, aka my feet speed up and I may not recover, so I absorb and extend (and push/pull the feet underneath the cm) appropriately so that I can optimize the cm's flow and remain balanced.

Again, not quite the same as literally slowing down as one can still be hauling much ass while doing so.

zenny
That's helpful, you sound more or less similar theoretically to Nailbender, and think that people like Chuck Martin have it wrong.

Which is fine -- there was another thread on here recently where the majority opinion likewise seemed to be that the coaches who produced Shiffrin were advocating a "wrong" drill and harmful movements.  The level of understanding on here often seems to outstrip the highest levels of the sport, and as regards moguls this may be an example.
Lol. Amazing. For all your bloviating you don't add much. It's info, not explanation or understanding but continued attempts to impress.
Quote:
Originally Posted by zentune

He he, wrong again ct (I really dig Chuck Martin). BTW, if your going to call out others here regarding their ability to ski the bumps, or anything else for that matter, it would be helpful for you to at least have an avatar depicting you skiing because, for all I know you could be some fat middle aged man living in his mothers basement who hasn't skied a day in his life ;-)

zenny

So, you really dig Chuck Martin, but explicitly disagree with one of his central ideas about bump skiing.  Ok.

As far as calling people out, based on experience I know that if we looked at film of the posters here skiing bumps, very few would do a good job absorbing.  If you think you have this covered, then don't worry about it for your own skiing.  However I know that for a group of 10 posters, if I asked them to write down, now, how much they absorb in bumps and then looked at film, they would be way off.

Likewise, the inability of people on here to grasp basic concepts, and the ability of a few posters in this thread to get away with routinely misstating or even inverting those basic concepts, may stem from a relative lack of exposure of many posters to the real-world application of these concepts.

What I would suggest, for instance, is that you, as someone who really digs Chuck Martin, go to a couple of his camps.  Or other similar bump camps.  If you conclude, having attended, that he's still wrong, and/or that you didn't get at all better at this A&E stuff, fair enough.  What I expect is that you'd find it a great experience that's immensely beneficial to your skiing.

Or, just keep posting on here about how you dig him, but he's wrong.  My age and my waistline have no bearing on those factors whatsoever.  And I ain't got no basement.

Quote:
Originally Posted by Tog

Lol. Amazing. For all your bloviating you don't add much. It's info, not explanation or understanding but continued attempts to impress.

Other than a simple, concise explanation of pumping & absorption, which I first gave about 2 years ago, and some basic technique points about what works, and what's possible and what's not, yes, I don't add much.  What I do add I concede is very basic.  That it continues to be contradicted by people trying to invert reality is a problem, but not my problem.

If you think there's been no inversions of reality, go pump the face of a bump for speed control.  Then tell me there's no problem.

Yawn, troll.

zenny
Quote:
Originally Posted by Tog

This is making the Centrifugal force discussions look simple.

Ghost with the swing i take it you disagree with the physicist that posted on quora? It's up above somewhere.

I'm not sure what physics you are asking me to agree or disagree with.  All I'm saying is how fast you can run up stairs while sustaining that speed on whatever slope you are on is how much you can reduce your speed by "anti-pumping" on that same slope, and exactly how tiring it will be to you.   How much energy you can dissipate by friction on the snow while flexing and absorbing is another story.   Any pumping or slowing down of a swing, whether against friction or against centripetal force results in a change in energy (kinetic and potential) due to work (force times distance) done by the legs on the system or by work (force times distance in the other direction) resisted by the legs.  Your legs can only do so much.

Quote:
Originally Posted by Ghost

... All I'm saying is how fast you can run up stairs while sustaining that speed on whatever slope you are on is how much you can reduce your speed by "anti-pumping" on that same slope...

This is not true, and ignores the mechanism at work.  For instance I know I can pump a bike on a pump track at 20 mph or so, and I can't run that fast.

Quote:
Originally Posted by CTKook

Quote:
Originally Posted by Tog

Lol. Amazing. For all your bloviating you don't add much. It's info, not explanation or understanding but continued attempts to impress.

Other than a simple, concise explanation of pumping & absorption, which I first gave about 2 years ago, and some basic technique points about what works, and what's possible and what's not, yes, I don't add much.  What I do add I concede is very basic.  That it continues to be contradicted by people trying to invert reality is a problem, but not my problem.
True. I exaggerated. What's up with the continued driveby shootings though?

As for TE, well hopefully he'll be back. The "final post" was all drama.
Quote:
Originally Posted by CTKook

Quote:
Originally Posted by Ghost

... All I'm saying is how fast you can run up stairs while sustaining that speed on whatever slope you are on is how much you can reduce your speed by "anti-pumping" on that same slope...

This is not true, and ignores the mechanism at work.  For instance I know I can pump a bike on a pump track at 20 mph or so, and I can't run that fast.

How fast can you pump that bike UP the mogul run?

Every pump you make on the flat pump track adds to your existing speed, it's cumulative.  So is the change in elevation when you are skiing downhill.

Quote:
Originally Posted by Ghost

How fast can you pump that bike UP the mogul run?

Every pump you make on the flat pump track adds to your existing speed, it's cumulative.  So is the change in elevation when you are skiing downhill.

I don't have to pump it up a bump run.  All I have to do is control speed on the descent.

New Posts  All Forums:Forum Nav:
Return Home
Back to Forum: Ski Instruction & Coaching