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Suppose a ball rolls without slipping down a rough inclined plane. I
am guessing you would like to call this an example of conservation of
mechanical energy: gravitational PE is converted into bulk
translational and rotational energy since static friction does no
work. This argument can be found in many intro books, but IMHO it's
nonsense.
By the same logic, if I start from rest and accelerate up to walking
speed without slipping on a level floor, my mechanical energy has
been conserved!!
Carl E. Mungan, Asst. Prof. of Physics 410-293-6680 (O) -3729 (F)
U.S. Naval Academy, Stop 9C, Annapolis, MD 21402-5040
mailto:mungan@usna.edu http://usna.edu/Users/physics/mungan/