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Ludwik writes:...
-----Original Message-----
From: Ludwik Kowalski [mailto:kowalskiL@MAIL.MONTCLAIR.EDU]
Most introductory textbooks teach that PEgrv = 0 can be
chosen arbitrarily at any distance between a particle and
the center of our planet. For example, at the sea level, at
the floor level, at the top of a laboratory table, at the roof
of that building, etc. A blunder or an apparent paradox?
Operationally, it's neither a blunder nor a paradox. The measurable
quantity is the work done between two points, equal within a minus sign to
the difference in potential energy. The zero point is "arbitrary" because
it cannot be uniquely measured.
George Spagna