OT: speed skating

so i noticed almost all the speed skaters have gold colored blades.. i remember CCM had a super tac blade (made by tuuk?) back in the day. some of my coaches over the years had them. eh. i guess it relates to the cooperall.

The blades look longer this year. Is this my imagination?

(Also, the ski jumpers' skiis look wider.)

longer skates, like longer skis, make you go faster. so most likely.
as for the skis, they are realy more wing than ski and i would immagine that they follow the same rules... more wing = more lift = more splintered femurs.

Why do longer skis make you go faster? I'd have guessed more surface area = more friction.

I think you're partly right. The other half to that answer is that the long ski offers, yes more friction, but with that and the length comes greater stability. Hockey skates noticeably move a little and don't hold a "line" as well on the ice.

You could have longer skis that are narrower with the same surface area. Longer skis are more stable in a straight line which is mostly what downhillers do and the stability/friction tradeoff may be beneficial. Don't know how this affects skis but with inflated devices such as tires, the contact patch area remains the same no matter how wide the tire, but the shape changes. It's a factor of how much the thing on top of the tire (or ski?) weighs.

For recreational skiers, length has gone down. Try to find a pair of 200cm recreational skis nowadays.

billhoward
For recreational skiers, length has gone down. Try to find a pair of 200cm recreational skis nowadays.

Is that because it's harder to turn, and faster skiis are actually a bad thing (i.e., harder to control, leading to more broken ankles)?

I know that when I skiied the relatively icey slopes in the east, my skis were almost impossible to control, but when I skiied the same length at Mt. Bachelor in powder, they were perfect. But they were only 180s, and I suck.

Long skis definitely are more stable in a straight line, as it is with long wheelbase cars and with rifles (vs. handguns). Skates, too, which is where this thread started. But the cut (curve) of the sidewall affects turning also. I believe the length also does a better job damping vibration (as does the composition of the ski).

That said, I think an engineer should step in here and provide an intelligent answer rather than the WAGs of government majors such as me.

billhoward
You could have longer skis that are narrower with the same surface area. Longer skis are more stable in a straight line which is mostly what downhillers do and the stability/friction tradeoff may be beneficial. Don't know how this affects skis but with inflated devices such as tires, the contact patch area remains the same no matter how wide the tire, but the shape changes. It's a factor of how much the thing on top of the tire (or ski?) weighs.

Tires aren't a useful comparison, really, because you're not trying to reduce friction in that case.

I don't *think* the contact area of a ski should effect friction, because friction is a function of the downward force (i.e. the skier's weight), not the surface area. I think canuck89 is probably right about stability.

Yes, I must have been a little sleepy this morning. In fact, the longer they are the less Frictional force there is per unit area. However, I do believe that spreading the friction out over a longer length (though it is the same force as jmh30 stated), would lead to greater stability.

canuck89
Yes, I must have been a little sleepy this morning. In fact, the longer they are the less Frictional force there is per unit area. However, I do believe that spreading the friction out over a longer length (though it is the same force as jmh30 stated), would lead to greater stability.

I recently received a confidential paper on friction from the Netherlands skating team. PM me if you are interested.

Whatever, Ugarte. I eat lunch with Bode Miller on occasion. PM me if you want more details on ski length and speed.

Jerseygirl
Whatever, Ugarte. I eat lunch with Bode Miller on occasion. PM me if you want more details on ski length and speed.

It would be better if you had an occasional après ski beer with Bode.

nyc94

Jerseygirl
Whatever, Ugarte. I eat lunch with Bode Miller on occasion. PM me if you want more details on ski length and speed.

It would be better if you had an occasional après ski beer with Bode.

Or an avant ski beer.

Yeah, well, you know, we chill at the lodge and all, but I'd rather emphasize the lunch part of it so you know I'm not just some snowbunny who bothers the Bodester at parties.

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

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

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.

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

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

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

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.

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

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..."

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.

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.

Don't be sorry, you helped.

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

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

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

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.

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.

I coulda sworn we established that 15 hours ago.

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.

One more thing I thought of while watching ski racing yesterday. A longer ski will have a longer turning radius than a shorter ski with a similar sidecut. If you compare the slalom skis that go up to the racers' noses, and watch the quick turns they are able to make, you will see what I mean. A ski with less sidecut (straighter) will also have a longer turning radius. This is ok in moguls, because the skiers are making short turns by skidding the skis back and forth between the moguls. In slalom racing, the skiers carve short-radius turns by using the shape of the ski. If you look at tapes from before the advent of the shaped skis, the slalom racers had to essentially step from gate to gate to get into the next turn quickly enough. Now the shape of the ski allows them to simply crank the turn within a small enough radius. Bode Miller was the first to really figure this out, and it allowed his career to take off.

haha. The point seems to need explaining every few posts in this thread. I agree with you. Just refer people to the top from now on.

This is the exact concept on which skates work. I do not know if it occurs on skis, due to the whole issue of lbs/inch that you mentioned. On skates though, the thin (and short) blade creates so much pressure that the ice indeed does melt and allows minimal friction (at least less than "skating" on ice itself).

Skis slide on a momentarily melted surface as well, but I don't understand physics well enough to know how length and width of the ski affect the force of friction.

canuck89
This is the exact concept on which skates work. I do not know if it occurs on skis, due to the whole issue of lbs/inch that you mentioned. On skates though, the thin (and short) blade creates so much pressure that the ice indeed does melt and allows minimal friction (at least less than "skating" on ice itself).

Actually, if you do the math, this is not true. You just need to apply too much pressure to lower the melting point of the ice significantly.

Sorry, i thought it was a given that the pressure was indicative of increased normal force per unit area. This force then leads to more friction, then heat, then melted ice. You are correct about pressure lowering the melting point.

canuck89
This is the exact concept on which skates work. I do not know if it occurs on skis, due to the whole issue of lbs/inch that you mentioned. On skates though, the thin (and short) blade creates so much pressure that the ice indeed does melt and allows minimal friction (at least less than "skating" on ice itself).

Here's an explanation of the current understanding of how ice skates slide. [www.exploratorium.edu] It's NOT melting the ice with the pressure, though that idea has long been taught. This page is just one in a whole site devoted to the physics of ice hockey. [www.exploratorium.edu] I highly recommend it.

more reputable than any of us at least.

Here's another article about why ice is slippery for those interested:

[www.nytimes.com]