Carve vs Flat wrt Speed

Hi,

I read in a book that when skiing on flattish terain, where you would normally ski in a straight line (because there is no need traverse the fall line to reduce speed), the fastest way to ski is not with skis flat on the piste, but to permenantly carve a very slight s-shape. The reason being there is less friction when carving (albeit very slightly) compared to when the skis are flat on the snow. If I think about this it makes sense. I tried this a lot when I last went skiing, and I think it is true, in that it I seemed to overtake my peers who were skiing flat. So, even though I skied a greater distance (the gentle s shape compared to a straight line), I seemed to get from A to B quicker. I'm not suggesting it is good to ski as fast as possible on flattish terain, but am interested to see if what I believe is true is actually true. Any views?

q

Surely there is less drag with an edged ski compared to a flat ski, because with an edged ski there is less ski surface in contact with the snow, meaning less friction/drag?

I'm sure Trencher is right and the skis would normally run fastest when they are flat to the snow. However, some of the new carving skis totally refuse to run in a straight line (I had some like this once) and you do have to slightly make them carve just to keep them running straight (ish).

Friction is a funny thing and it's not directly affected by surface area - just the force pushing the two surfaces together and the coefficient of friction of the materials.

However, pressure is affected by surface area as it is equal to the force per unit area. So, I reckon that the pressure on the snow would be much greater when the skis are on their edges as compared with when they are on their flats, and that this pressure would be too much for the snow which would give way and hence greatly increase the friction between the ski and the snow and slow you down.

I might be wrong, of course, but this is what I reckon happens.

Ally

PaulBryanBill wrote:Surely there is less drag with an edged ski compared to a flat ski, because with an edged ski there is less ski surface in contact with the snow, meaning less friction/drag?

Perhaps it has something to do with the gliding over the snow with, as trenches said, the right wax whereas with edges they won't have any wax so will tug and pull as they dig IMO the snow instead of washing over it

When you first start carving on skis or board, it feels like someone just released the hand brake. As you start to carve at increasingly higher edge angles, you start to feel the loss of speed on each turn, and you need increasing steep terrain. Carving only feels fast compared to skidding turns.

Another factor I forgot, is that when travelling at high speeds on snow with your edges flat friction is further reduced because frictional heating causes local surface melting of the snow which lubricates the contact area between the skis and the snow. I remember having to learn this for the effect of pressure melting when ice-skating.

But I think when you go on the edges of your skis the increase in pressure is too much for the (shear strength?) of the snow which causes it to break away from the snow underneath greatly increasing the coefficient of friction between the snow and the skis. You only have to think of how you can spray someone with snow whilst doing a hockey-stop!

I should imagine the mats on the dry ski slope must be designed so that if you are travelling on them on your flats then friction is minimum but as soon as you go on your edges the extra pressure makes the spiky mat bits give way so the skis 'fall' into them and friction is then greatly increased.

I'm not at all sure my theories are correct, but if they are then one would expect that going on your edges wouldn't make any difference if the snow was rock hard ice instead - and that was kind of what I experienced on that really hard glacial ice at Tignes. I found I couldn't brake or turn by digging my edges in.

Anyone got any more ideas on this? It's a very interesting question.

Ally

If anyone wants to know any more about the physics of ski-ing, I've found a whole website here which explains a lot of interesting things. Like, for example, apparently the reason it's so hard to move on very wet snow (like in the spring) is because a vacuum is created under the skis which sucks them down.

And I was right about the film of water being created under the skis when they're on their flats, which is why you get those nasty icy patches in high traffic areas like on the narrow blue runs, because the water re-freezes as ice, not snow.

There's also a whole load of complicated stuff to do with vectors about why you slow down when you go across the slope.

http://www.mechanicsofsport.com/skiing/basic_mechanics/using_resistance.html

Ally