THE SIDECUT FACTOR


From a perspective of sound principles of science, the forces shown in THE BALANCE PUZZLE: CONNECTING THE DOTS, don’t fly even though the graphics are more comprehensive than most explanations of the mechanics of edge grip (set) which only show a resultant force emanating from CoM acting at the inside edge of the outside ski. But this was just the opening position. I have a lot of dots to lay out and connect before the balance issue in skiing coalesces.

Some may have questioned the need for the resultant force to be an angle of less than 90 degrees to the transverse aspect of the base of the outside ski of a turn in order for the edge to grip. If two equal and opposite forces are aligned in the same plane, wouldn’t this be the textbook definition of balance? Technically, yes. But there are lot of pieces of the puzzle missing. First, the Resultant Force (R) acting on the Centre of Mass (CoM) is not an applied force. It is an attractive force that is acting to pull CoM towards an object; in this case towards the inside edge of the outside ski. And I have not yet shown an applied force. But the big missing factor is the sidecut geometry of the ski. For some reason, this never seems to be included in explanations I have come across on the mechanics of  edge grip.

Here is the second sketch from my post THE BALANCE PUZZLE: CONNECTING THE DOTS. I have added a graphic element and a notation to show the point where the inside edge of the outside ski meets the snow as ground zero. It is my position that the mechanics, biomechanics and physics of edge grip and a base of support in the form of a platform that is a continuous source of reaction force for the outside foot emanate from ground zero.

 

Ground Zero

Here is the same graphic with the width of the shovel superimposed over the width of the ski at the waist (under foot).  The sketch does not accurately represent the dynamics of ski camber in a turn because the ski would normally be deformed into reverse camber by the forces acting on it. When the width of the shovel and tail that make up the sidecut geometry are added to the equation it becomes obvious that a resultant force that passes through ground zero will not apply the forces needed to cause the shovel and tail to grip and the ski to bend into reverse camber against the reaction force acting at at the limit of the shovel (and tail, not shown). Any explanation of edge grip and carving forces that does not consider the mechanics of sidecut geometry does not fly.

 

Sidecut