On Thu, 18 Dec 2003 02:23:00 -0600, R wrote:

On Wed, 17 Dec 2003 21:40:51 -0800, "Peter Duniho"
wrote:


Weight cannot be detected except
when a body is not in free fall.

Of course it can. Simply note your acceleration, multiply by your mass, and
you get your weight. The acceleration itself is proof of the force called
"weight". Without a force, there is no acceleration. In free fall, the
*only* force acting on the object is weight.

So in orbit an object has no weight.

Again, yes it does.

However, the spacecraft is moving in a straight line along the
geodisc. There is no way to distinguish a "weightless" (freefall)
object moving in a straight line along the geodisc of a gravitational
field from a "weightless" (non-accelerating) object that is nowhere
near a gravitational field. Both travel in straight lines along the
geodisc. What you're saying is dead-on in the Newtonian sense, but
as far as relativity is concerned, an object in freefall is synonymous
with an object not affected by a gravitational field. An object not
affected by a gravitational field by definition has no weight.

The Earth is "accelerating" towards the sun in the Newtonian sense
every day, just as the Sun is "accelerating" towards the center of the
galaxy, but I'm guessing all but the most insufferable graduate
student is willing to leave these non-negligable forces out when they
report their weight on their driver's licence.

-R

Bad example. All forces, of whatever kind, are totally irrelevant to
the weight on that driver's license.

http://physics.nist.gov/Pubs/SP811/sec08.html

Thus the SI unit of the quantity weight used in this
sense is the kilogram (kg) and the verb "to weigh" means
"to determine the mass of" or "to have a mass of".

Examples: the child's weight is 23 kg

American Society for Testing and Materials, Standard for Metric
Practice, E 380-79, ASTM 1979.

3.4.1.2 Considerable confusion exists in the use
of the term weight as a quantity to mean either force
or mass. In commercial and everyday use, the term
weight nearly always means mass; thus, when one
speaks of a person's weight, the quantity referred to
is mass.

Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/