Skiing up hills:

  • Unlike, flat surfaces where the force gravity is canceled out by the normal force, it is not when going up a hill. As shown in the Free Body Diagram (FBD); there are two components to the force of gravity. Therefore; in order to ski up a hill you must not only exceed the maximum force of friction, but must exceed the force of gravity as well. This becomes harder and harder as the hill gets more steep.
    https://farm1.staticflickr.com/87/228393229_af9297ade5.jpg

                     https://farm1.staticflickr.com/87/228393229_af9297ade5.jpg

http://wordsandphotographsdotcom.files.wordpress.com/2013/11/pb160288.jpg