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# Rusty I'm bored now - Page 2

Self imagined super hero abilities seems more fun

So, it's correct that on a frictionless, surface, making perfect lossless carved turns, one has the same speed at the bottom of the hill then if they straight lined it?

Quote:
Tog--are you asking if it is theoretically possible to actually make turns with no friction (ski-snow, or air friction)? I think that the answer is no, it is not even theoretically possible to do that in practice. It is only theoretically possible to do it in theory!

No, the question was if making a turn, even a theoretical friction free one that also doesn't loose energy through smearing etc., would change anything about the energy status of the skier. Simply through making an arc. But I guess the force is coming from the mythical frictionless turning mechanism so nothing changes.

Quote:
Originally Posted by Tog

So, it's correct that on a frictionless, surface, making perfect lossless carved turns, one has the same speed at the bottom of the hill then if they straight lined it?

In theory I have had to much wine to answer that. In reality I will anyway.

Yes it is true, but the question is. Is it even theoretically possible to do linked lossless turns?

Lossless means not only zero friction, it also means all deflections and impacts need to be fully elastic (i.e. you bounce back with the same speed)

I'm not sure of the answer, but consider e.g. PSI-man, who obviously does not work with his legs.

When his mass travels from one side to the other it will not be in line with the skis travel direction, and when he reaches the other side his mass will be deflected. If this deflection is at least partly non-elastic the snow will absorb energy so it is not lossless. If the deflection is elastic he will bounce back, but can he make turns bouncing this way? I'm not sure PSI-man could keep his balance, but maybe you could construct another theoretical device that could.

If PSI man is making a turn when he comes to the bottom part of the energy will be rotational, so the speed is slightly less.

Quote:
Originally Posted by Tog

A feather and a hammer fall at the same rate without air resistance.

How about a feather and a bowling ball?

That point about transfer of energy due to deflection is a key point. That is a separate thing from friction, and in my opinion it's something we are using in skiing intentionally by making ski turns. Friction sorta is what it is and generally we are obsessed with waxing our skis and reducing friction. Even when our goal is speed control, waxed skis perform better, turn better and even allow better speed control, while reducing friction to the greatest extent possible. Friction is generally not desirable in skiing,, nor is it necessary to slow down
Quote:
Originally Posted by borntoski683

That point about transfer of energy due to deflection is a key point. That is a separate thing from friction, and in my opinion it's something we are using in skiing intentionally by making ski turns. Friction sorta is what it is and generally we are obsessed with waxing our skis and reducing friction. Even when our goal is speed control, waxed skis perform better, turn better and even allow better speed control, while reducing friction to the greatest extent possible. Friction is generally not desirable in skiing,, nor is it necessary to slow down

Absolutely, and I think that it probably is part of the secret of speed control in the upper C.

Quote:
Originally Posted by borntoski683
Friction is generally not desirable in skiing,, nor is it necessary to slow down

I haven't read the other long thread, so my apologies if this is covered. But if everything was really frictionless, I wonder if snow would pile up and hold well enough to effectively turn or stop against. The snow wouldn't have any friction against itself, although perhaps the water adhesion between drops/crystals would be enough - I don't know the mechanics of why snow sticks together and what role friction plays. But if friction between snow particles is important in skiing, and it was removed, you could probably stop, but the bits of snow you pushed around would go flying off quickly sliding like you are. In that case, you'd have to push a lot of snow to lose speed, and probably take a really long time to stop if you could.

nobody is saying snow is frictionless.  We are way off into the theoretical now.

That may be all right, though, BTS. In theory, we should all go skiing and get back to the real. But in reality, it's summer.

Could be a long one!

Best regards,

Bob

Quote:
Originally Posted by borntoski683

nobody is saying snow is frictionless.  We are way off into the theoretical now.

So we're only removing the friction between the skis and the snow? In that case, the amount of snow that moves when you turn would take a tiny bit of energy out of the system, and would slow you down a tiny bit as well. If you could turn without moving the snow, then you wouldn't lose energy, as stated before.

There is some friction between our skis and snow in reality.  Anyone who has gone too long without waxing can attest to that.  The theoretical discussion about WHAT IF there was no friction is an attempt to isolate certain principles of physics for sake of discussion.

And I agree Bob.

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Originally Posted by dbostedo

So we're only removing the friction between the skis and the snow? In that case, the amount of snow that moves when you turn would take a tiny bit of energy out of the system, and would slow you down a tiny bit as well. If you could turn without moving the snow, then you wouldn't lose energy, as stated before.

moving snow...is not the deciding factor

Energy is never lost.  it is converted or transferred.  If that's what you mean by lost..that its transferred.. energy can be transferred even if the snow is not moved.

all that moving snow means is that was broken away from the ground.  In fact I would suggest that if a lot of snow breaks away, then any speed control effects are reduced, but so are turning effects.

Edited by borntoski683 - 5/22/15 at 4:06pm
Quote:
Originally Posted by borntoski683

moving snow doesn't have anything to do with it.  Moving snow actually would NOT transfer energy anywhere, that would result in loss of turn tightness..the energy simply caries the skier on a wider arc.

Moving snow of necessity takes some energy. There's no way for snow to move and energy not to be transferred to it. If energy is transferred to it, it's got to come from somewhere.

a very small amount of energy in that case.  I re wrote my last reply while you are responding, sorry, read my updated version.

basically if the snow breaks away from the ground then only a small amount of energy is transferred to it...enough to move a very light substance a short distance.  Yes I agree that is some of the energy, but that is not what we've been discussing so far which is much more massive amounts of energy relatively speaking.

and its not neccessary for the snow to break away to do what we've been discussing, though that is also another interesting factor to consider.

Again, back to "reality" of sorts--I suspect that friction--and anything that causes "energy bleeds"--plays a very interesting role in skiing. We make our skis as slippery as possible, wax them with temperature-specific wax and, if we're really serious and energy loss matters, wear aerodynamic clothing to minimize air resistance. We practice techniques for turning that minimize the energy loss from skidding and that maximize gliding, and even often measure the quality of the turn by how little energy it bleeds away. Turns that bleed less energy are not only faster and win more races, but also more efficient as far as involving the least amount of energy expenditure on our part to ski the chosen line. For most expert skiers, everything they do, measure, and practice is intended to minimize friction and "energy bleed."

(As an aside, I recognize that what I just wrote certainly does not describe all skiers, and indeed, it may well be the single biggest differentiator between expert skiers and skiers stuck in the "intermediate rut." While experts tend to conserve energy with a passion, many, if not most, recreational skiers intentionally bleed energy. It is the essence and the fundamental objective, whether they know it or not, of their techniques, as "slowing down" and managing speed is almost always the primary purpose of their turns. My first paragraph does not apply to these skiers.)

But even for the experts trying to eliminate friction, minimize "energy bleed," and maximize efficiency and glide, friction plays a very large role in skiing. Yes, it would be theoretically possible to ski and manage speed without it, but really, we don't need to ski without it, and we exploit its effects even as we try to minimize them. Even in the best of turns, there is substantial friction and energy loss. At higher speeds, too, air friction (which increases with the square of the velocity) has a tremendous slowing effect, and expert skiers "use" that as well with tactical brilliance. On many gentler runs, we may reach speeds of nearly terminal velocity, and whether we think about it or not, I suspect we savor the ease of managing speed that takes over at that point. If it were slipperier, or if we were more aerodynamic, we might well just go a little faster, in order to attain the same ease.

I suggest that it is a love-hate-love affair that we have with friction. We do everything we can to eliminate it, but I'll bet we'd miss it if it suddenly vanished entirely. It's hard to say, for sure, and I'll be first in line for it if someone comes up with a complete friction-eliminator (or just a better wax).

In any case, to make this practical (at least, for anyone who can still get out for some turns), one of the best exercises you can do is to try to ski each turn as far around the "circle" as as you can--beyond just "across the hill," trying to go back uphill as far as possible, before finally letting go of that turn and gliding back downhill the other way. How far around the "clock face" can you get? Try to top that on the next turn. It's one of the few things we can do that are actually measurable. The better the turn, the less energy you will "bleed off" and the farther around the clock face you'll be able to glide. And of course, if you can just keep going around and around the clock face without losing any speed, you've not only eliminated all friction, but also learned to make the "perfect" turn.

Good luck!

Best regards,

Bob

Quote:
Originally Posted by Bob Barnes

How far around the "clock face" can you get?

I could swear I read a thread on here at some point where someone said they could actually do a full circle. Is it possible on any kind of hill? I've only seen video where someone sort of did a full circle carve on a flat section.

Yes it is possible to go all the way around; been there, done that, not a perfect circle though.  I stopped doing that a few years ago after almost getting creamed going uphill when follower did not expect me to turn uphill.

Sure it is, DBostedo. But not from a standing start on the circle.

A very good skier can do it on nearly any run with good snow, enough pitch to get up some speed, and enough width to make a clean arced carved turn all the way around. If there is a less steep "shelf," it's even easier if you make the 360 carve on that less steep section. Even going twice around the circle is not out of the question. Please be extremely cautious and aware of traffic if you try this!

In the right circumstances, almost anyone can ski a carved 360 degree turn. For example, imagine a steeper hill that leads to a flat area that is bounded by a slope on one side--like the intersection between two trails (please be VERY careful about cross traffic, and don't even think about trying this if there is oncoming traffic on the trail you're intersecting). If you carry speed from the steep onto the flat, and then begin a smooth, carved turn that takes you immediately up the the side hill or the other trail, it takes only a minimum of skill to ride that carved turn all the way around.

But again, even for the best skiers, on the best of snow, considerable speed and energy will bleed away as you ski around the arc. You could not do it from a standing start--at least, you could not pass all the way back uphill through your original starting point (without adding energy with your poles or some skating-type exertion).

Best regards,

Bob

Quote:
Originally Posted by cgeib

Quote:
Originally Posted by Tog

A feather and a hammer fall at the same rate without air resistance.

How about a feather and a bowling ball?

Alright now that was just mind blowingly cool. The drop on the Moon is short so you can sort of not believe it. But not that one! Just that one demonstration is worth millons towards the cost of building that structure.

RIP Rusty.

Quote:
Originally Posted by Tog

So, it's correct that on a frictionless, surface, making perfect lossless carved turns, one has the same speed at the bottom of the hill then if they straight lined it?

No, the question was if making a turn, even a theoretical friction free one that also doesn't loose energy through smearing etc., would change anything about the energy status of the skier. Simply through making an arc. But I guess the force is coming from the mythical frictionless turning mechanism so nothing changes.

Tog, if you build a roller coaster out of superconducting rails and suspend yourself with magnets and put yourself in a vacuum, you'll get pretty darn close to see that the turns will make no difference to the final velocity.  Also, if you had a sheet of ice with razor sharp edges in a vacuum it wouldn't be too far off either.  You maybe would have a hard time with those experiments on black diamond slopes, but you could do those experiments in practice on skates on very gentle slopes to see how turns make little difference without friction opposing the direction of travel.

Quote:
Originally Posted by The Engineer

Quote:
Originally Posted by Tog

So, it's correct that on a frictionless, surface, making perfect lossless carved turns, one has the same speed at the bottom of the hill then if they straight lined it?

No, the question was if making a turn, even a theoretical friction free one that also doesn't loose energy through smearing etc., would change anything about the energy status of the skier. Simply through making an arc. But I guess the force is coming from the mythical frictionless turning mechanism so nothing changes.

Tog, if you build a roller coaster out of superconducting rails and suspend yourself with magnets and put yourself in a vacuum, you'll get pretty darn close to see that the turns will make no difference to the final velocity.  Also, if you had a sheet of ice with razor sharp edges in a vacuum it wouldn't be too far off either.  You maybe would have a hard time with those experiments on black diamond slopes, but you could do those experiments in practice on skates on very gentle slopes to see how turns make little difference without friction opposing the direction of travel.

I may not be a scientist nor an engineer, but I think we ski on a mountain, not in a vacuum.

This reminds me of a joke - How many ski instructors does it take to screw in a lightbulb?

Quote:
Originally Posted by Trekchick

This reminds me of a joke - How many ski instructors does it take to screw in a lightbulb?

Umm... two, but it's gotta be a really big light bulb?

Quote:
Originally Posted by Trekchick
This reminds me of a joke - How many ski instructors does it take to screw in a lightbulb?

Umm....
We don't know because they're still trying to define "light bulb"?
Quote:
Originally Posted by Tog

Umm....
We don't know because they're still trying to define "light bulb"?

I was also thinking something like...

20 - 1 to put in the bulb, and 19 more to tell him how he could have turned it better.

Doesn't matter. Without friction, it isn't going to stay in anyway. Not even in a hot tub.

Best regards,

Bob

Three, one to change the bulb the others to tell him nice turns.

Quote:
Originally Posted by Trekchick

I may not be a scientist nor an engineer, but I think we ski on a mountain, not in a vacuum.

Exactly.  That's why friction is the dominant force behind all of our skiing methods.  When you imagine doing any of our methods without friction in a vacuum on super conductors, they are not very effective for speed control.  Using this information we can figure out the best way to control speed using horizontal turns across the mountain, or as Dan Dipiro called it, vertical turns in the bumps.  Same difference, both control speed mostly for the same reasons.  On groomed runs, turning without scraping has an elegance that helps control speed by spending less time on steep slopes, and in the bumps A&E has an elegance by doing the same thing in the vertical direction to spend less time on steep slopes, and that makes a difference because of friction.  It's pretty cool.  Wind resistance is part of it too, but I think it's a small part, because many people model snow as a fluid that has friction that depends on speed as well.  So just for simplicity let's call it friction so we don't always have to say friction/wind resistance.

Quote:
Originally Posted by Trekchick

Quote:
Originally Posted by The Engineer

Quote:
Originally Posted by Tog

So, it's correct that on a frictionless, surface, making perfect lossless carved turns, one has the same speed at the bottom of the hill then if they straight lined it?

No, the question was if making a turn, even a theoretical friction free one that also doesn't loose energy through smearing etc., would change anything about the energy status of the skier. Simply through making an arc. But I guess the force is coming from the mythical frictionless turning mechanism so nothing changes.

Tog, if you build a roller coaster out of superconducting rails and suspend yourself with magnets and put yourself in a vacuum, you'll get pretty darn close to see that the turns will make no difference to the final velocity.  Also, if you had a sheet of ice with razor sharp edges in a vacuum it wouldn't be too far off either.  You maybe would have a hard time with those experiments on black diamond slopes, but you could do those experiments in practice on skates on very gentle slopes to see how turns make little difference without friction opposing the direction of travel.

I may not be a scientist nor an engineer, but I think we ski on a mountain, not in a vacuum.

This reminds me of a joke - How many ski instructors does it take to screw in a lightbulb?

Quote:
Originally Posted by The Engineer

Quote:
Originally Posted by Trekchick

I may not be a scientist nor an engineer, but I think we ski on a mountain, not in a vacuum.

Exactly.  That's why friction is the dominant force behind all of our skiing methods.  When you imagine doing any of our methods without friction in a vacuum on super conductors, they are not very effective for speed control.  Using this information we can figure out the best way to control speed using horizontal turns across the mountain, or as Dan Dipiro called it, vertical turns in the bumps.  Same difference, both control speed mostly for the same reasons.  On groomed runs, turning without scraping has an elegance that helps control speed by spending less time on steep slopes, and in the bumps A&E has an elegance by doing the same thing in the vertical direction to spend less time on steep slopes, and that makes a difference because of friction.  It's pretty cool.  Wind resistance is part of it too, but I think it's a small part, because many people model snow as a fluid that has friction that depends on speed as well.  So just for simplicity let's call it friction so we don't always have to say friction/wind resistance.

I see you edited my post that you quoted.

Edited by Trekchick - 5/23/15 at 5:03pm
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