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# Why can't kids beat adults in the same race? - Page 2

In our club races we had a rule like yours - Age and treachery beats youth and skill!

It is clear that weight has a advantage.  My team mate did an experiment and wore a 30# weight vest.  He was significantly faster.  As a 175# guy, I routinely beat 200#ers of similar ability, but that does not account for me getting my @\$\$ kicked by 100# women.

Finally, how do you account for Ted Ligety and Julian Mancuso who are relativley small compared to other big time Alpine athletes?

Quote:
Originally Posted by Ghost

If you do the math, and I don't have time now (but I have done it), you will see that the heavier skier will have the higher terminal velocity.  Well, a bit of time; It works something like this.  Net accelerating force pulling down = [( mass x g ( sin(theta) - Mu Cos(theta) )   - ApCd v^2  ] and acceleration is g(sin(theta)-cos(theta) -[ [ApCd v^2] /mass].  You can see the second term, which gets subtracted is a greater percentage of the net force and the accealertion for the lighter skier.  The greater surface of the larger skier is not enough to compensate for the mass effect (m varies as L^3, but projected area Ap varies as L^2)

Thanks for the lesson, even though that has nothing to do with what I said. I guess you meant, all friction. I just always refer to air friction as drag. My fault.

Quote:
Originally Posted by cswalker21

I've seen a lot of replies that revolve around "the heavier skier has more force pulling him down the hill" etc. But what about inertia? Shouldn't terminal velocity be independent of mass and only relate to drag? The only thing I remember from physics class is that the greater pull of gravity on a heavier falling object is offset my its larger inertia so that in the absence of air resistence, a feather and a stone would fall at the same speed. Would that not apply to an object sliding down an icy slope as well? Pardon my ignorance, I was just wondering. My guess would be that adults of similar skill level generally win (old slow-pokes like me excepted) because of greater strength, not greater weight. Thoughts?

No. cswalker21, you are just confusing ideas and terms from physics into a blob. How could terminal velocity be independent of mass? Terminal velocity is the velocity an object has when the drag force is equal and opposite to the gravitational force. In a vacuum, what you said is true for masses in free fall in a gravitational field; we don't ski in vacuum. You should have felt this before assuming you have skied. Drag cannot be neglected, unless you were racing on a near flat slope.

I think there is more to it than air drag, too.  According to freshman physics, surface friction is proportional to normal force, which scales with mass.  But that is a big oversimplification, mostly meant to make homework porblems solvable.  (Well, its not too bad for smooth hard surfaces in contact, but when does that apply?)  Now I haven't tried to do a quantitative drag estimate, so maybe my gut feeling is all wrong.  Ghost, hhave you ever checked if reasonable parameters work in the simple equation?

These complex concepts become abundantly clear every year at the Cub Scout Pinewood Derby when we see how a 5 ounce brick will destroy a 4 ounce perfectly shaped airfoil with the truest alignment imaginable.

Weight first

Alignment second

Aerodynamics third

Only when the course becomes more turny does agility and strength begin to factor in..

uote:
Originally Posted by Bill Miles

It's called the cube-square law. If an object or person is twice as large in all dimensions, it will have eight times the weight (and gravitational force and approximate base drag friction), but only four times the frontal area (and aerodynic drag). Makes a bigger difference at higher speed.

Thanks Bill.

That's basically it.

The more you weigh, the less important drag force is RELATIVE TO THE OTHER FORCES INVOLVED.  That doesn't mean it's not important; it is important; it's just More important if you have less gravity to counteract it. The faster you go the more important it is, so being big 's a bigger advantage in DH than SL.

Quote:
Originally Posted by crgildart

Weight first

Alignment second

Aerodynamics third

Only when the course becomes more turny does agility and strength begin to factor in..

So we're fat, old, bald and incompetent

Quote:
Originally Posted by veteran

So we're fat, old, bald and incompetent

Speak for yourself, we are not all bald.

But is it air drag or ski drag?  There still seems to be a difference at very low speeds on nearly flat slopes, where that classical velocity squared term is very small.

Quote:
Originally Posted by mdf

But is it air drag or ski drag?  There still seems to be a difference at very low speeds on nearly flat slopes, where that classical velocity squared term is very small.

On the flats weight works against you instead of for you in the same way it worked for you on a slope.  On the flats, or near flat it is your body actions determining your momentum more than gravity.  A turny course incorporates more flats or near flats as you cross the fall line more instead of heading down it.  This is why lighter folks (i.e. Ligity) can excel in slalom more where heavier folks can excel more easily in a forgiving NASTAR type GS course..

Interesting exercise would be to determine which has greater impact on speed.  Friction or Aerodynamics?  In my experience, I would suggest aerodynamics have a greater impact than a competently waxed ski.

My only data is that on our home GS course which runs about 30 seconds, a GS suit on on competent racer will make at LEAST a one full second difference.

You can also look at NASTAR pacesetter qualification where the athletes () race with coats and no coats.

Math is hard.

Quote:
Originally Posted by pat

Interesting exercise would be to determine which has greater impact on speed.  Friction or Aerodynamics?  In my experience, I would suggest aerodynamics have a greater impact than a competently waxed ski.

My only data is that on our home GS course which runs about 30 seconds, a GS suit on on competent racer will make at LEAST a one full second difference.

You can also look at NASTAR pacesetter qualification where the athletes () race with coats and no coats.

Math is hard.

I'd argue that a poorly chosen wax has far more impact than a perfectly chosen wax does... especially over a ski with no wax at all.  And that is over everything.  If you missed the wax by a mile, skiing naked won't help you.

Quote:
Originally Posted by pat

Interesting exercise would be to determine which has greater impact on speed.  Friction or Aerodynamics?  In my experience, I would suggest aerodynamics have a greater impact than a competently waxed ski.

My only data is that on our home GS course which runs about 30 seconds, a GS suit on on competent racer will make at LEAST a one full second difference.

You can also look at NASTAR pacesetter qualification where the athletes () race with coats and no coats.

Math is hard.

Depends on the course (of course). I raced our town Super-G a few years ago and was right up there in training runs. When everybody else stripped for the race I was a suddenly getting beaten by J4s. In a slalom that's not going to matter as much. Wax helps a lot, but I don't think it could ever have an impact like that.

It seems I shave about a half second off a 20 second NASTAR run just by losing the jacket so there is something to it.  But, someone weighting 40 pounds less than me can't touch me..

You can play with PhysicsMan's model and back out all these effects.

But one bad turn and you are done in a flat course.

Don't tell PSIA.... but if you can't carve edge to edge while staying on the racing line and tucking whenever possible...you won't like NASTAR and beer league.

One slight mistake and you can never recover the time.

Some kids are rocket fast because they generate edge angles that adults can mostly dream about.

The difference between a real jacket and a suit in NASTAR is 4-5 handicap points.

This leads to old geezers like me to suit up when it is 3 degrees and windy with the hope that the pacesetter will come jacketed.

It feels pretty good to beat an 8 handicap pacesetter straight up when you are 35 years older.....

Quote:
Originally Posted by crgildart

On the flats weight works against you instead of for you in the same way it worked for you on a slope.  On the flats, or near flat it is your body actions determining your momentum more than gravity.  A turny course incorporates more flats or near flats as you cross the fall line more instead of heading down it.  This is why lighter folks (i.e. Ligity) can excel in slalom more where heavier folks can excel more easily in a forgiving NASTAR type GS course..

I'm not thinking of a course, but of a truely straight and flat, like a runout where you put off skating a s long as possible.  I usually am one of the last to stop, and I don't start out bombing faster than everyone else.  Although  I did wax my own skis (and not my son's) halfway through the trip...

Quote:
Originally Posted by mdf

I'm not thinking of a course, but of a truely straight and flat, like a runout where you put off skating a s long as possible.  I usually am one of the last to stop, and I don't start out bombing faster than everyone else.  Although  I did wax my own skis (and not my son's) halfway through the trip...

That all adds up. At the end of your glide the wax is gonna be huge. If you have some good  flouro on there, you'll just keep oozing along when the other guys are stuck to the ground.

Quote:
Originally Posted by Spooky

No. cswalker21, you are just confusing ideas and terms from physics into a blob.

This doesn't actually surprise me. Physics was never my strong suit, and now it appears the one thing I remember is wrong. I can deal with that.

Here's a new wrinkle on it, though. Stipulating that more weight leads to more speed within a relevant range, there has to be a point beyond which this is no longer true. Otherwise World Cuppers would look like sumo wrestlers. So, what are the factors that make more weight detrimental past a certain point, and what would be a good formula to determine an optimal weight?

The closer the course is to a straight vertical drop, the more weight matters.  The more horizontal the forced line is and the harder the turns are the less weight matters.

Quote:
Originally Posted by cswalker21

This doesn't actually surprise me. Physics was never my strong suit, and now it appears the one thing I remember is wrong. I can deal with that.

Here's a new wrinkle on it, though. Stipulating that more weight leads to more speed within a relevant range, there has to be a point beyond which this is no longer true. Otherwise World Cuppers would look like sumo wrestlers. So, what are the factors that make more weight detrimental past a certain point, and what would be a good formula to determine an optimal weight?

Technique matters the most...further skiing, is an open skill sport, requiring quick reflexes, balance, agility, etc.  Not somthing ideal for a sumo wrestler.

Sumo wrestler might make a good contender for outright speed record in speed skiing thou, where its just straight and steep.

Quote:
Originally Posted by Ghost

The closer the course is to a straight vertical drop, the more weight matters.  The more horizontal the forced line is and the harder the turns are the less weight matters.

Assuming you're going in a straight line. The reality is Nastar gets set on a relatively flat hill and the course is non technical compared to something the J1's, 2's, and 3's are skiing. Technique matters more than weight in the kids vs adults deal, and commensurately, the youngsters will pretty much crush most adults like ants when things get steep and turny. Even at the lower levels, they'll be on much more even footing.
Edited by markojp - 10/26/12 at 10:38pm
Quote:
Originally Posted by cswalker21

This doesn't actually surprise me. Physics was never my strong suit, and now it appears the one thing I remember is wrong. I can deal with that.

Here's a new wrinkle on it, though. Stipulating that more weight leads to more speed within a relevant range, there has to be a point beyond which this is no longer true. Otherwise World Cuppers would look like sumo wrestlers. So, what are the factors that make more weight detrimental past a certain point, and what would be a good formula to determine an optimal weight

I've only seen the course at T-ride and it is basically just going straight down the slope. I skied it and it seems you reach your terminal velocity for the slope just past 3/4 the way down. World cup? I don't know anything about racing, but it would seem you'd need to have skills controlling your turns and speed as well as finding the fastest line...I dunno.

Quote:
Originally Posted by Skidude72

Quote:
Originally Posted by cswalker21

This doesn't actually surprise me. Physics was never my strong suit, and now it appears the one thing I remember is wrong. I can deal with that.

Here's a new wrinkle on it, though. Stipulating that more weight leads to more speed within a relevant range, there has to be a point beyond which this is no longer true. Otherwise World Cuppers would look like sumo wrestlers. So, what are the factors that make more weight detrimental past a certain point, and what would be a good formula to determine an optimal weight?

Technique matters the most...further skiing, is an open skill sport, requiring quick reflexes, balance, agility, etc.  Not somthing ideal for a sumo wrestler.

Sumo wrestler might make a good contender for outright speed record in speed skiing thou, where its just straight and steep.

No.

Sumo wrestlers are a totally different shape... which must be accounted for as width of body tends towards bolling ball vs angled beam. And at speed air friction/drag becomes the main limiting factor... growing exponentially. And muscle is more dense than fat. A big strong sleek skier would win in steep and straight....a sumo wrestler would not.

In the real world vs idealized physics models for learning there are many inflection points and regime changes that we have to take into consideration... and we haven't even broached biomechanics yet.
Btw... I agree w skier dude here... just not the sumo part.
Quote:
Originally Posted by justruss

No.
Sumo wrestlers are a totally different shape... which must be accounted for as width of body tends towards bolling ball vs angled beam. And at speed air friction/drag becomes the main limiting factor... growing exponentially. And muscle is more dense than fat. A big strong sleek skier would win in steep and straight....a sumo wrestler would not.
In the real world vs idealized physics models for learning there are many inflection points and regime changes that we have to take into consideration... and we haven't even broached biomechanics yet.

Not saying sumo wrestlers aren't fat, but it's a gross misperception to think that these guys aren't very very strong, very quick, and more flexible than most of us will ever be. Not that they're going to be great skiers by any means, but go watch some clips and look up 'Chinofuji' for fun. The man was a beast. . Now back to you regularly scheduled interwebz argument.

Oh, no doubt the top Sumo wrestlers are incredibly strong, agile, etc. They may be fat, but they're also upper echelon athletes.

But the main point-- of this totally tangential phase of the discussion-- was about body shape re air friction/drag. They're big and wide... and round. The biomechanics bit has a lot to do with the limitations of two (non-quantum level sized) physical objects being unable to occupy the same space, such as a stomach and a thigh of tremendous size.

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