Friction & Skiing

I had learnt about friction in school physics as the force which hinders motion. The official definition of friction is "Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other." Delving deeper, we understand that it is basically the reluctance of any body to move. Hence one would need to overcome this frictional force to ensure that the body moves in the first place! And besides that once the motion begins, one has to continuously keep applying extra force to ensure that the frictional force is balanced and the motion continues.

Most times being an engineer, the focus is to reduce the effect of this friction to ensure easy motion. There are large number of lubricants available whose sole purpose is to reduce friction as it is in most cases considered to be an undesirable phenomenon in physics. However, it is often overlooked that the complete absence of friction could lead to uncontrolled motion and hence could lead to disasters. 

Last week, when I was at ski resort at a place called Auli, Uttarakhand, I encountered this dimension of friction. Standing on ski on an icy surface makes one realize how the complete absence of friction could make motion as difficult as the presence of it. The relative friction between ski and the ice surface to quote the least is minuscule and in most practical cases can be considered to be close to zero. 

The first encounter with this zero friction phenomenon came when I was wearing my ski. It is very common to see people slip even before they take their first step with the ski as the mind as well as feet are not habituated to motion without friction. I experienced a similar feeling and was on my knees even before I stood on my feet with skis on them.

After getting enough training, I learnt how to habituate yourself to this zero friction motion and also various techniques to ensure that there is some friction which is created either by weight transfers or the orientation of the ski which would later on come in handy in controlling as well as maneuvering motion.

To understand how to do this, one has to understand the construction of Ski . The main body of it is a flat surface which has almost zero possibility of generating any friction. The edges however are sharp and hence would cut into the ice and thus help in hindering motion and thus controlling it. Hence, the greater the exposure of edges to the direction of motion, the more will be the hinderance to it. Hence edges act as the braking force - Expose the edges more when you want to brake and reduce the exposure when you want to accelerate. It sounds simple but execution takes a little bit more time just like learning any other art.

The first lesson was to ensure that the ski pointing downhill are always in the shape of "V". The bigger the V, the higher is the friction as more of the edge comes in contact with the downhill slope and the smaller the V, the lesser is the friction and hence lesser is one's control. 

Next comes the management of body weight which is as important as management of the "V". When there is higher weight on one leg as compared to other, there is higher relative friction of that Ski which would lead to slower movement of that leg and hence lead to smooth turn in other direction. It is like drawing a circle using a rounder, The sharp edge fits into the paper and doesn't move and the one having pencil moves forming a circle. Same as the case with the ski. The only difference being that even the sharp edge moves too and so does the other edge! The only objective is to ensure that the other moves faster leading to a turn. So one can assume that your legs are the steering wheels of the ski. Turn left by putting more weight on left leg and vice versa.

So the next time you ski, Look how physics works and experience its magical impact on your movement!