The problem with the "what a scale reads" definition of "weight" is that
you have to decide *which* scale you're going to read. Why should it
necessarily be the one you're standing on? What about the one between
your head and the ceiling when you stand up in a room that is too short to
accommodate your height? What about the one between your back and the
hand of a friend as she pushes you out the door? What about the one
between your neck and the rope wrapped around it as ... Well, you get the
picture.
Since *all* contact forces can be turned into scale readings, the only
sensible procedure is to add the forces they indicate as vectors and say
that the vector sum of all contact forces that you exert on other objects
is your weight. This brings you perilously close, however, to concluding
that your weight is equal to your mass times negative your acceleration.
Hmm. What a simplifying idea that might be. I wonder if anyone else has
ever thought of it?
John
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A. John Mallinckrodt http://www.intranet.csupomona.edu/~ajm
Professor of Physics mailto:ajmallinckro@csupomona.edu
Physics Department voice:909-869-4054
Cal Poly Pomona fax:909-869-5090
Pomona, CA 91768-4031 office:Building 8, Room 223