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Powder Skiing Techniques

post #1 of 10
Thread Starter 
An old adage that I have heard for skiing in powder is the three S's: steer 'em, suck 'em up, squeeze the knees. This is supposed to mean, as I understand it: use a rotary turning mechanism, unweight at turn initiation, use a narrower stance to help keep both legs at the same level in the snow. The "Powder" article in the Complete Encyclopedia of Skiing is more or less consistent with this, although the emphasis is on carved (non-skidded) turns rather than the rotary mechanism.

I had the opportunity last Thursday and Friday to try this out at Vail. I don't have much experience or expertise in powder/crud conditions, but did make some observations:

1) It seemed to be require less muscular effort to start turns with an edging mechanism rather than rotary, although I'm sure I was using both mechanisms in reality. I was using Fischer RC4 skis with a 10-meter side-cut radius.

2) It was easiest when making short radius turns on steeper pitches, and most difficult on shallow terrain.

What say the experts? I'd be grateful for some discussion of this topic. Thanks. Jeff.
post #2 of 10

Powder skiing is all about making adjustments. Forgetting about crusts and different skiable layers within the snowpack, the depth of the snow and the moisture content or heaviness of the snow can create two possible differences:
1) The experience of riding in the snow as opposed to on the snow,
2) Increased resistance to turning.
The pitch of the slope is the third variable that determines the volume for the adjustments you need to make. The kinds of adjustments that we make include speed, turn shape, weight distribution/leg stance width and "height off the base layer".

If the snow depth and moisture content are not great enough to support your weight, you will merely sink through the powder and ride on the underlying "base" layer of snow. Otherwise your path through the snow will have a third dimension that you will need to adjust to. Let's call it height above the base layer. The "suck em up" or unweight at turn initiation advice addresses this, but there is more. At the start of the turn (when you are more across the fall line than in it), you want to be highest off the base layer and on a flat ski for a fraction of a second. From there, you will be pushing the tips down into the snow as you increase edge angle into the new turn. In the fall line, you want your skis to be on a maximum edge, but also deflecting off the base layer (if possible). This will aid the unweighting/suck em up/ retraction move to get the skis closer to the surface. Think about a roller coaster when you are turning. Beginners in powder often benefit from forced bouncing on their feet while in a traverse, then turning on an up bounce.

When you're in the snow, you're going to have more resistance from the snow pushing against your skis and your body. This will slow you down going downhill as well as making it harder to turn the skis across the hill. Slower downhill speed is generally not a problem. At least until you find yourself the first person to be tracking out of a flat spot. You may find yourself seeking steeper pitches to go faster and that can start messing with some people's heads. The easiest asjustment is to make "shallower turns" (i.e. less across the fall line) to increase speed. Maintaining sufficient speed is critical because it helps gives you more force to fight the resistance of the snow. [ side note to Physics Man - if F=MA - why does a higher velocity appear to give you more force ].

Two other means to overcome increased resistance are rotary and edging. More rotary simply means you are pushing the skis harder via ankle, knee, femur, hip and or shoulder rotation. It's effective. We use it when we must. But it's a lot of work. And it's a lot more work if you are in the back seat. Which is why a lot of intermediate skiers get tired very quickly when trying to ski powder. With modern shaped skis, increased edging gives you increased turning. Even in "loose" powder snow, shaped skis will turn when they are put on edge. Although the effect is less when the powder is lighter, the need is less as well. When the ski is edged it flexes more too. This also helps to increase turning power to fight the increased resistance from powder snow. So in general we like to rely more on more edging to overcome snow resistance than using more rotary.

In powder snow, we generally like to get our feet closer together and our weight distribution closer to 50-50 than when we ski on groomed snow. The farther we get from a 50-50 distribution, the greater the snow depth difference of our feet (again this is paradoxically a bigger problem in heavier snow). This makes for unequal resistance from the snow. Which then makes it real difficult to make smooth rythmic movements. One of my guiding principles is to let weight distribution happen. Feet closer together lets the weight be closer together. But it does not matter what your focus is. Squeeze your knees, move your feet, focus on your weight distribution, whatever - as long as you don't get caught with one foot up and one foot down.

Hopefully, you've been able to see how the variables work and thus better understand the sensations that you experienced. The art for powder skiing is to skillfully recognize snow depth, texture and slope pitch, then apply a combination of edging, rotary, turn shape, speed control, weight distribution and 3 dimensional skiing in response. The result will be smooth rythmic turns, a floating sensation and transformation into a Powder Pig!
post #3 of 10
Good response...

Maintaining sufficient speed is critical because it helps gives you more force to fight the resistance of the snow. [ side note to Physics Man - if F=MA - why does a higher velocity appear to give you more force ].
Don't confuse Momentum with Force.

Momentum can be defined as "mass in motion." All objects have mass; so if an object is moving, then it has momentum - it has its mass in motion. The amount of momentum which an object has is dependent upon two variables: how much stuff is moving and how fast the stuff is moving. Momentum depends upon the variables mass and velocity. In terms of an equation, the momentum of an object is equal to the mass of the object times the velocity of the object.

Momentum = mass * velocity
In physics, the symbol for the quantity momentum is the small case "p"; thus, the above equation can be rewritten as

p = m * v
where m = mass and v=velocity. The equation illustrates that momentum is directly proportional to an object's mass and directly proportional to the object's velocity.

The units for momentum would be mass units times velocity units. The standard metric unit of momentum is the kg*m/s. While the kg*m/s is the standard metric unit of momentum, there are a variety of other units which are acceptable (though not conventional) units of momentum; examples include kg*mi/hr, kg*km/hr, and g*cm/s. In each of these examples, a mass unit is multiplied by a velocity unit to provide a momentum unit. This is consistent with the equation for momentum.

Momentum is a vector quantity and is fully described by both magnitude and direction. To fully describe the momentum of a 5-kg bowling ball moving westward at 2 m/s, you must include information about both the magnitude and the direction of the bowling ball. It is not enough to say that the ball has 10 kg*m/s of momentum; the momentum of the ball is not fully described until information about its direction is given. The direction of the momentum vector is the same as the direction of the velocity of the ball. In a previous unit, it was said that the direction of the velocity vector is the same as the direction which an object is moving. If the bowling ball is moving westward, then its momentum can be fully described by saying that it is 10 kg*m/s, westward. As a vector quantity, the momentum of an object is fully described by both magnitude and direction.

Sorry to be so long winded.

post #4 of 10
I like to get my students first bouncing in the snow. But, the bounce happens with a pressing down of the feet, not a lifting of the upper body. Press down with the feet and then relax and let them come up again. Do this a couple of times in a traverse to get the feeling.

This extension down and retraction up is a key component of powder skiing. When the skis come up you can apply the rotary and yes a little edging/tipping motion (although the skis will not edge so much as they will tip and allow you to press down again with the skis going in a different direction, i.e. turning.

Work on keeping your upper body quiet and facing downhill. Shorter turns are easier to keep speed down. Hold your hands out in front, but not necessarily up high. High hands will cause you to sit back and you want to be centered on your skis.

If a measure of how well you carve a turn is the width of your track, then efficient powder skiing will result in the best carved turns of your life.

post #5 of 10
the bounce helps, but I'd rather see skiers learning crud first. the transition to pow is natural from there.
post #6 of 10
Thread Starter 
Thank you for the detailed and helpful analysis. I think I can clarify the issue about velocity and force. It was stated previously in the thread: "Maintaining sufficient speed is critical because it helps gives you more force to fight the resistance of the snow. [ side note to Physics Man - if F=MA - why does a higher velocity appear to give you more force ]"

The relationship between velocity and force is as follows. F does equal M A (Newton's Second Law), and so A = F / M. "A" is the skier's acceleration or change in velocity over time. Velocity V = A T, where T is the elapsed time (assuming for simplicity that A does not change). V, F, and A are all vector quantities (they have both magnitude and direction), so V can either increase or decrease in magnitude over time depending on the direction of A (which is the same direction as F).

The skier is making turns across the fall line. To simplify things, assume he spends some time directly in the fall line and some time directly perpendicular to the fall line.

In the fall line gravity predominates over friction and drag (as long as the slope is sufficiently steep). Therefore A is in the same direction as V, and the skier's velocity magnitude increases with time.

Across the fall line friction and drag (mostly friction) predominate over gravity. Therefore A is in the opposite direction to V, and the skier's velocity magnitude decreases with time.

If V decreases below some threshold in the "across the fall line" phase, then the skier can no longer effectively make turns, and thus flounders in the snow.

Therefore V must be allowed to increase above some higher threshold during the "in the fall line phase" to prevent this.

The bottom line is that it is not true to say that "higher velocity gives you more force." A force acting over time causes velocity to change. The velocity can increase or decrease depending on the relative directions of the velocity and force vectors.

The skier, by managing the forces acting on him, must control his velocity to keep it above the threshold where he can no longer effectively ski. He manages those forces primarily by controlling his direction with respect to the fall line.
post #7 of 10
Eeeks - this is turning into a physics class.

While it may not be true that higher velocity = more force, it has been my experience that higher velocity makes turning easier in heavy snow. My suspicion is that this is because more force is applied to the snow. Higher momentum certainly makes sense. I'm just having trouble applying the f=ma equation when the a=0 (constant velocity). Is there more force against the snow?
post #8 of 10

In any turn there is always acceleration. This acceleration might not show up as change in speed but as a change in the direction of travel.

post #9 of 10
OK, I'll bite.

It seems like the fundamental question that TheRusty is considering is why does higher speeds make turning so much easier in powder. The main physical mechanism involved is "lift", and you don't need to use equations to understand it (at least qualitatively).

By “lift”, I am not referring to conveyances that get you to the top of the mountain or spacers you put between your bindings and your skis, but the force or “lift” that keeps airplanes up in the air. Imagine a ski going through bottomless powder with its tip higher than its tail. The force of the snow hitting the bottom of the ski pushes the ski upwards. This is “lift”. The faster you go (for a given up-angle and snow density), the more lift you generate. Put your hand out a side window of your car at 5 mph versus 30 mph and feel the difference in the wind forces on it. The same thing happens to a 5 mph skier versus a 30 mph skier in powder. Lift doesn’t occur on packed snow – it only occurs when your skis are fully immersed IN snow and can move in all three dimensions, including upwards.

The extra lift generated by going at higher speeds in powder benefits several types of powder turns:

1) If you tend to ski powder smoothly and don't tend to do a lot of unweighting to make turns in deep powder, higher speeds mean that your skis will generally stay in a higher, less dense layer in the snow, so, your skis will be easier to pivot.

2) OTOH, if you make porpoising turns in powder, the extra lift you get from your skis at high speeds means that you will need to rely less on muscular unweighting to get your skis to come up to the surface, or even jump above the surface (where they can be pivoted very easily).

3) Finally, there are powder turns that involve minimal pivoting, banked turns. If you are on a wide open slope, you can make high speed banked turns in deep powder, but you can only do this at fairly high speeds. The physical mechanism behind this type of turn is exactly the same as in a banked turn in an airplane. The lift generated by the tilted wings (or skis) pushes you not just upwards, but also towards the inside of the turn, deflecting the skier (or plane) from a straight path. Go slow, and there is minimal lift and hence minimal force to deflect you from a straight line should you try to bank. Instead, you will just fall over.

This is very different from what happens on groomers. There, you can execute very slow speed RR track turns using just angulation (ie, without any lateral motion of your CM), but these don’t work at low speeds in the 3D environment of deep powder. Imagine trying to angulate/edge at 1 mph in 3 feet of new powder. Your skis will simply descend to the bottom on a sloped path to the side instead of going straight down, but they certainly won’t turn at such low speeds without substantial rotary input.

Finally, (the) Rusty, also asked about a feeling that you can exert “more force” on the snow when going fast, even in a straight line.

On first blush, one would think that this is impossible from the F=ma arguments mentioned above (ie, no centrifugal forces, etc.), but I have a suspicion about what you are talking about. It might be that you are feeling your skis bust through irregularities in the powder/crud that you know you wouldn’t be able to bust through at lower speeds, and hence you realize that you *must be* exerting more force on them at higher speeds to do this. This is absolutely correct. You *are* exerting more force on them. Its just that you are exerting the higher forces for a short period of time at the higher speeds. Its much like a fast moving bullet can go through a wall – it exerts huge forces on the wall, but only for a very short period of time. Am I close to what you are taking about? If not, we can hopefully get some time to chat on Sunday up at WT, but I suspect we’ll have some decent sized crowds to deal with.


Tom / PM
post #10 of 10
Thanks PhysicsMan,

Yes, the last bit was what I was after. The faster the bullet goes, the more force from deceleration is available. But the feeling of extra turning power from faster speeds in powder is a continuous phenomena. I think the difference comes from the continuous force of gravity. Once a bullet is fired (parallel to the earth), gravity does not provide any more acceleration to get through the wall (horizontally). But a skier traveling downhill is continuously tapping into gravity. It's like the gun going off over and over again.

If a skier was to enter a flat section of powder, it's intuitively obvious that the faster one travels entering the flat region, the farther one will travel before stopping. The greater the change in velocity, the more force is applied. the more force applied, the greater the distance traveled.

So, looking at it that way, it is easy to believe that at any one point in time, a skier travelling faster down the hill is applying more force to the snow. At the next point in time, gravity will have continued to provide acceleration (force). Coincidentally, that accleration is just enough to offset the deceleration caused by snow friction. Thus velocity remains constant, but the greater (potential) force from the higher velocity remains.

But it still seems like a paradox to me. Could it be possible that the slower you travel, the greater the force of friction on the ski? We know that a ski travelling over the snow surface melts the snow and creates a thin lubricating layer of water and thus reduces friction. A ski with zero velocity would have no lubrication. Such a ski is certainly hard to turn in powder. Although a lubricating layer would not directly help to get the ski moving laterally, it's easy to see how the properties of the ski (sidecut and camber) could convert greater forward movement into greater lateral movement. With less force lost to friction, one would need to disperse more force into the snow via lateral movement to maintain a constant velocity. This could cause the feeling of more power.

hmmm - something is still missing ..... I want to see "A" going into the snow.
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