Bending the skis

Bending the skis Subscribe Pub

Let's take an in-depth look at bending the skis, the why and the how of the bending and how that is useful.

Paul Lorentz has a good article on how shaped skis use bending to shape the turn: Ski Bending

Paul has produced one of my most favorite skiing videos on Youtube:

Enjoy - there are a few more interesting articles on his website as well.

A few facts about the physics if ski bending (skio to next section to escape dorkiness):

the ski bends with pressure and angles when there is snow interaction (i.e. the snow is strong enough to hold the ski)
however, more pressure does not mean more bend - once the ski is supported along its length, more pressure will most often not cause more bending, unless the snow still gives in
the major force involved in ski bending is the Centripetal Force, which applies along the ski's edge, mostly underfoot, as a reaction to the skier's pressure
the Centripetal Force in physics is the force that deviates a body from a linear motion into circular motion, see Centripetal force
the bigger the angles, more of the Ground Reaction Force becomes Centripetal Force
unlike constant circular motion, where the Centripetal Force is constant, in skiing, it is variable along the turn
the more the ski turns across the direction of travel, the bigger the opposing force, as the mass of the skier creates more force
however, remember more force and more pressure does not equate more ski bend

So one may be left wondering, if I can't bend the ski with pressure anymore, can't I increase the edge angles at the end of the turn and create more bend?

Vaulting and trampolines

As to the energy stored in a bent ski, here is some hands-on experimenting:

Whether the ski itself is acting like a "trampoline" or is it mostly an effect of vaulting, there is much debate still.

This is more experimenting:

The consensus appears to be though that, although there is lots of energy in the ski itself, there is much more to be had by "vaulting" the body over the edges of the skis, from the forces of the turn.

Basically, as the skis turn across the direction of travel, towards the bottom of the turn, a lot of pressure develops, which we can use to generate and/or change the Impulse. We can think of it as a trampoline, but the energy powering it comes from the turn itself rather than your efforts (as would be say hopping), at the expert levels.

Also, here is a very good demonstration and discussion of ski bending at different angles:

Courtesy of Tom Gellie

Implications

Let's do some quick logic exercise, around bending a ski...

the more you tip the skis on edge, the more they bend - true
the more angulation you have at the right time, the more you can edge the skis (speed and slope notwithstanding) and the more they bend - true
the more weight there is on an edged ski, the more it bends - false
the more weight there is on an edged outside ski, the more it bends - false