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Re: definition of weight (again)



Part of the problem is we must have two definitions (at least) because we
speak to non physicists and it's impolite to correct them, especially if they
are communicating.

I prefer an operational definition i.e. what the bathroom scale says [I have a
high tech one-:)], even when it is supporting one in an elevator.

I suppose the point of the thread is what physicists use when communicating
among themselves -- in that case why not do what we accept from scientific
bodies e.g. SI. This is a job for NBS or AIP no?

bc (not totally serious)


Larry Smith wrote:

This debate seems to resurface every year (or is it every semester?), but
it would be nice if we could all agree on the definition of weight.

Here's what Hewitt says on page 159 of Conceptual Physics (9e): "In
Chapters 2 and 4 we defined weight as the force due to gravity on a body,
mg. Your weight does have the value mg if you're not accelerating. To be
more general we now refine this definition and say that the weight of
something is the force it exerts against a supporting floor or a weighing
scale. According to this definition you are as heavy as you feel."

Kirkpatric and Wheeler (4e) generally agree with Hewitt's _revised_
definition, with the caveat that they say weight is the support force
itself (the "reaction" force of Hewitt's weight, equal, of course, in
magnitude, but opposite in direction).

But Serway and Beicher (5e) say on page 119: "the weight of an object,
being defined as the magnitude of F_g, is mg." Other than being a scalar,
Serway's definition agrees with Hewitt's original "unrefined" definition.

Hobson, in Physics: Concepts and Connections, p. 99, seems to agree with
Serway but keeps the vector: "The weight of an object refers to the net
gravitational force exerted on the object by all other objects." Griffith
(The Physics of Everyday Phenomena p. 64) agrees that it is a vector: "The
force of gravity acting on an object is what physicists commonly refer to
as the weight of the object."

This issue is important enough by itself, but it also affects how we talk
about weightlessness and the definition of g.

I guess I'm looking for a little closure on this, folks. Is there any to
be had? Consensus, please.

Thanks,
Larry