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Re: Apparent weight



John Mallinckrodt wrote:

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.

An operational definition is just that. If you want to operationally
redefine the meter, you can, but it won't be the accepted operational
definition. I don't hold fast to my operational definition, but a
definition was asked for and the one offered is the one I give my
students. It avoids a lot of problems.

The non-contact force mg acting toward the center of the earth on an
object is NOT the weight of the object according to my definition,
although, for bodies in static equalibrium on the earth's surface, the
numerical value of the mg force is nearly equal to the numerical value
of the weight. (It is the normal force that is equal to the weight.)

Once our students get this separation of weight from the mg force, then
they are far more successful with solving dynamics and statics problems.

Roger

================================
| Roger A. Pruitt, PhD |
| Department of Physics |
| Fort Hays State University |
| Hays, KS 67601 |
| Ph. (785) 628-5357 |
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