OT: speed skating

[Josh '99]

That's good name-dropping technique right there, switching from the actual name into the nickname "Bodester".  I give it a 9.7.

[Ack]

**] If an object (ski/skate) is sliding across a uniform surface (snow/ice), the force due to friction is going to be the same regardless of the shape/size of the material.  However, the force is distributed over a wider contact area.  Think of skating flat-footed (where all the metal is touching the ice) vs. skating on your toes (just a point of metal is touching the ice).  Same force applied on the ice by the skate (your weight), but the point force (small contact area) could tend to stick more into the ice.  The friction force is the same, but there is more resistance with the shorter skate.  Make any sense?  my $0.02

[sen '08]

What matters more in skiis these days is the shape.  The parabolic skiis make it easier to turn and therefore easier to control.  Also, the more curve in the ski, the shorter and wider they are, so they have about the same surface area.

[Trotsky]

Stupid question: are downhill skis supposed to lift you off the hill (like wings), or stick you to the hill (like a spoiler)?

[nyc94]

[quote Trotsky]Stupid question: are downhill skis supposed to lift you off the hill (like wings), or stick you to the hill (like a spoiler)?[/quote]

I don't think they are supposed to do either.

[nr53]

the material skis are made out of also makes a difference. Parabolic skis are allowed to flex while turning because the middle where your foot is attached is basically off the ground until any force is applied (yay for momentum) The energy of your turn is stored in the flex of your skis and released when you come out of your turn. This added "bounce" helps propel you out of a turn. Hence, the shape of the ski allows you to turn easier while the more difficult it is to flex a ski the more energy it gives back at the end of a turn meaning you can turn faster. As far as the aerodynamic nature of skis, they don't provide lift in either direction but my Atomic's have a bumpy surface on the top (think golf balls) thats supposed to keep the ski from vibrating at high speeds for more stability. Don't ask me if it really works, but it makes them look cool.:-)

[KeithK]

[quote Trotsky]Stupid question: are downhill skis supposed to lift you off the hill (like wings), or stick you to the hill (like a spoiler)?[/quote]I can see it now.  "Why did you ski off of that cliff?"  "I meant to turn, but suddenly my skis caught the breeze and whoosh! I was flying over the cliff..."

[cth95]

A stiffer ski with materials such as titanium and wood in the core will add damping while keeping the ski from flexing too easily at higher speeds.  There are also new technologies consistently coming out such as the surface on Atomic skis to increase damping.  This helps keep the ski from chattering at higher speeds, therefore keeping more of the ski in constant contact with the snow.

The downside to a stiffer ski is that it is less forgiving.  Softer skis are used by beginners, intermediates, and lighter weight skiers so the ski will bend easier as they turn.  This allows the skier to steer the ski, rather than the other way around.  Relatively softer flexing skis are also used for skiers who prefer to ski in the trees and moguls, which requires many, quick, short turns in which not as much force is generated to bend the ski as in high speed cruising.

As far as ski length goes, both new technologies like the ones used to dampen the skis and the shaped or parabolic skis allow for shorter lengths.  Shorter lengths are able to maintain contact and control better than in the past because of the better dampening materials, while shorter skis have better edge hold than in the past because the edge is on a curve rather than a straight line.  This means that a shorter ski still has a similar overall edge length in contact with the snow.  The shape also allows the ski to curve simply by rolling up on edge rather than requiring the technique and strength to flex the ski into a curve like we used to have to do with straight skis.  All things being equal, a longer ski will be more stable at high speeds, but more difficult to turn.

You want to keep good contact with the snow, but this comes more from proper balance, edging, and pressure than from the ski itself.  By maintaining pressure on the inside of the boot cuff and down through the ball of the foot on the downhill leg, the ski will hold an edge and the skier will maintain control.

Sorry about the length of this.  I was an instructor for 4 years.  Once I started typing the thoughts kept flowing.

[Jim Hyla]

[quote cth95]A stiffer ski with materials such as titanium and wood in the core will add damping while keeping the ski from flexing too easily at higher speeds.  There are also new technologies consistently coming out such as the surface on Atomic skis to increase damping.  This helps keep the ski from chattering at higher speeds, therefore keeping more of the ski in constant contact with the snow.

The downside to a stiffer ski is that it is less forgiving.  Softer skis are used by beginners, intermediates, and lighter weight skiers so the ski will bend easier as they turn.  This allows the skier to steer the ski, rather than the other way around.  Relatively softer flexing skis are also used for skiers who prefer to ski in the trees and moguls, which requires many, quick, short turns in which not as much force is generated to bend the ski as in high speed cruising.

As far as ski length goes, both new technologies like the ones used to dampen the skis and the shaped or parabolic skis allow for shorter lengths.  Shorter lengths are able to maintain contact and control better than in the past because of the better dampening materials, while shorter skis have better edge hold than in the past because the edge is on a curve rather than a straight line.  This means that a shorter ski still has a similar overall edge length in contact with the snow.  The shape also allows the ski to curve simply by rolling up on edge rather than requiring the technique and strength to flex the ski into a curve like we used to have to do with straight skis.  All things being equal, a longer ski will be more stable at high speeds, but more difficult to turn.

You want to keep good contact with the snow, but this comes more from proper balance, edging, and pressure than from the ski itself.  By maintaining pressure on the inside of the boot cuff and down through the ball of the foot on the downhill leg, the ski will hold an edge and the skier will maintain control.

Sorry about the length of this.  I was an instructor for 4 years.  Once I started typing the thoughts kept flowing.[/quote]Don't be sorry, you helped.

[nr53]

indeed, more thought and detail than i felt like going into **]

[Drew]

I always believed that the longer ski created more friction, which heated the ski, which after time melted the snow, to actually reduce friction and make it more slippery over the course of a run or race.

Cheers,
Drew

[The Rancor]

for ski jumpers it makes for more lift, but for downhill its spreads the friction out and makes you go faster somehow. right?

[canuck89]

A longer ski does not create MORE friction, it just spreads it out.  The Force of friction is a product of a constant and the normal force (basically what a skier weighs).  Therefore, the amount of friction between the skis and the ground remains the same as if the ski were 1 foot long instead of ~6 (length is not in the formula for frictional force).  Overally, stability is the advantageous aspect of longer skis.

[Josh '99]

[quote canuck89]A longer ski does not create MORE friction, it just spreads it out.  The Force of friction is a product of a constant and the normal force (basically what a skier weighs).  Therefore, the amount of friction between the skis and the ground remains the same as if the ski were 1 foot long instead of ~6 (length is not in the formula for frictional force).  Overally, stability is the advantageous aspect of longer skis.[/quote]I coulda sworn we established that 15 hours ago.  :-P

[ftyuv]

Are we really sure that's true though?  After all, on skis there's more than just simple friction stuff going on.  As the skis press down on the snow, they melt it a bit (actually, I think I read a study that claims it's not exactly melted;  the atoms bounce up-down more than side-side, whereas in a liquid they'd move around randomly).  Although the total normal force you exert down is the same, the pounds per square inch would be different for different net areas, and this would surely have an effect on that melting phenomenon, which would in turn affect one of the relevant materials (namely the ground), which would in turn affect the coefficient of friction.  I haven't taken physics since high school (a conceptual course at CU notwithstanding), but that's how it seems like it'd be to me.