The list has just been through a big discussion on this topic, and there is no unanimous agreement on the definition. Some say, as you have suggested, that it is "what a spring scale would read." Others say that it is the mean (or local) gravitational attraction of a dominant planetary body (Gmm'/r^2). According to your definition, astronauts in the ISS indeed are 'weightless' whereas planetary-gravitationally they are not.
Bottom line: State a definition, show how that definition affects the solutions to problems, advise that others might use a different reasonable definition and may work the problem differently. The results must agree as to the behavior, subject to transformations of coordinates.
As long as one understands the definition of a word and how it relates to the physical measurements involved, agreement on which definition is correct is not important. On the other hand, casual use of a word might create a mis-conception.
There's a early QM story regarding German and American theorists. They kept getting phase factors in various calculations that were different by pi. They eventually realized that the Germans were using left-handed coordinates while the Americans were using right-handed. Once they understood the definitions, their results were identical.
Bill
-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Espinosa, James
Sent: Wednesday, November 17, 2010 12:06 PM
To: Forum for Physics Educators
Subject: [Phys-l] Weight?
What is weight? Sometimes, when the origin of the lay word has not been technically defined (as is done in mathematics), it helps to find its etymology. The etymology of "weight" goes back to "lift." It, therefore, appears that the weight of a body has been considered an upward force. I tell my students that weight is a force of support, pointing vertically upward. From Newton's laws it follows that weight is equal and opposite to the force (pull) of gravity on the body. It can then be shown that N = mg. What I emphasize to the students is that mg (pull of gravity) is due to the whole Earth, including India, China, the Pacific Ocean, etc.; but N (the force of support is due only to the floor which is in contact with the soles of the shoes. The agent of the force is completely different on the two sides of the equation. I do not attempt to confuse the students with corrections that might exist from the Earth's rotation, Special Relativity, General Relativity, Quantum