GROUND SUPPORT


In this post, I will discuss where the source of ground or GRF lies in relation to the forces applied by the outside or stance foot of a skier.

Explanatory diagrams of the forces of skiing typically show a resultant force (R) of the components of gravity (G) and centrifugal force (C) acting on the centre of mass (COM) of a skier. The vector of the resultant force (R) emanating from COM is shown acting at a point in the vicinity of the inside edge of the outside ski. If a force diagram is sophisticated, it might show a ground reaction force (GRF) acting at the inside edge of the outside ski or even the centripetal component of centrifugal force.

Regular

The overly simplistic nature of such force diagrams infers that control of the edge angle of the outside ski requires nothing more than an alignment of R with inside edge. In this context, the effect of the width of the ski under foot on the skier as shown in the image below is of no consequence.

Fats

The influence of the mechanics of both of the above ski configurations on the skier are inferred to be the same even though they are dramatically different as shown in the overlay below.

Overlay

The reality of such force diagrams is that they represent a static moment in time; a snapshot that tells nothing of the dynamic nature of the forces at play. In order to accurately represent the dynamic forces, force diagrams must include the load from the weight W of COM and especially how and where the load is transferred to the outside foot of a turn, to the ski and from there to the point that I call Ground Zero. Ground Zero is where the forces of the snow and skier meet. The forces at the skier/ski equipment/snow interface should be the subject of intense discussion and debate. More than simply being important, understanding and managing these forces is fundamental to skier balance and the global control of COM essential to a biomechanically sound technique.

Force diagrams like the one shown below should be the minimal starting point for meaningful dialogues on the forces of skiing.

With Central Axis