(Richard Harrison) wrote in message ...
Dave Shrader wrote:
"If that assertion (I am 240 pounds "mass" on earth. That`s a fact. I am
240 pounds "mass" on moon. That`s a weird assertion!) is true, who
changed te density of the moon??"

Mass is the bulk of matter though not necessarily equal to its weight. A
mass weighing 240 pounds on earth weighs less on the moon because there
is less mutual attraction between the moon, of much smaller mass than
the earth`s mass, and the object which weighs 240 pounds on the earth.

Mass is the property which provides a body with inertia. Mass is the
mechanical analogy of inductance. Mass is equal to the weight of a body
divided by the acceleration due from gravity (32ft./sec./sec.). This is
an expression of Newton`s 2nd law of motion: F = MA, thus M = F/A.

Newton`s 1st law says that to move a body at rest, enough force must be
applied to overcome its inertia.

Newton`s 3rd law says that for every action there is an equal and
opposite reaction.

The gravitational force of the earth is stated as "1".

Not really; the standard acceleration due to gravity (more accurately,
of free fall), or an approximation of the local acceleration, is
sometimes expressed as 1 lb/lbf, or 1 kgf/kg, or 1 gee. But it isn't
dimensionless, and it is also often expressed with units in which its
numerical value is not one (always, if you are using SI units, the
modern metric system).

The gravitational
force on the moon is about 0.16 that on earth, so an object weighing 240
pounds on earth would weigh only 38.4 pounds on the moon.

That's certainly true enough, at least for one definition of weight.
But it has nothing to do with Dave Shrader's "I am 240 pounds "mass"
on moon. That`s a weird assertion!" You are talking about something
different from mass.

Gene Nygaard

Gene Nygaard wrote:
"You are talking about something different from mass."

Yes. An orbiting astronaut may be weightless due to a particular balance
of forces, but he has mass and inertia.

We have weight and force. Either weight or force may be expressed in
pounds or kilograms. The conversion number I remember and use is: 2.2
pounds equal 1 kilogram.

The dictionary says the kilogram is a unit of mass, since a mass can
conveniently be accurately represented by an object. That particular
object is a cylinder of platinum-iridium alloy, called the international
prototype kilogram. This object is preserved in a vault at Sevres,
France.

Work may be meaasured as force times distance or as pounds times feet.
Power is work per unit time. Power may be expressed as foot-pounds per
minute. James Watt`s horse was said capable of working at a rate of
33,000 foot-pounds per minute. I calculate that as 250 kilogram-feet per
second or 76.2 kilogram-meters per second.

Best regards, Richard Harrison, KB5WZI

On Sun, 28 Sep 2003 02:02:54 -0500 (CDT),
(Richard Harrison) wrote:

Gene Nygaard wrote:
"You are talking about something different from mass."

Yes. An orbiting astronaut may be weightless due to a particular balance
of forces, but he has mass and inertia.

We have weight and force. Either weight or force may be expressed in
pounds or kilograms.

This is the only place you deal with Dave Shrader's comment.

The fact that you are implying he SHOULD NOT be surprised that his
mass on the moon would be 240 lb is totally obscured by the rest of
your ramblings.

The conversion number I remember and use is: 2.2
pounds equal 1 kilogram.

That will be acceptable for many purposes, iff

1. You are smarter than Roger Halstead and realize that you cannot
get six significant digits in your result by using this conversion
factor.

2. You are dealing with pounds in their normal definition as units of
mass, not pounds force.

You ought to be remembering both 1 lb = 453.6 g and 1 lbf = 4.448 N,
or something along those lines.

The dictionary says the kilogram is a unit of mass, since a mass can
conveniently be accurately represented by an object.

Of course, that applies to a troy pound standard as well (in the
United States from 1828 until at least after 1850, and probably until
1893 when the avoirdupois pound was redefined as an exact fraction of
a kilogram, our primary standard was a particular artifact known as
the Troy Pound of the Mint, and our avoirdupois pounds were units of
mass defined as an exact fraction of this standard).

That particular
object is a cylinder of platinum-iridium alloy, called the international
prototype kilogram. This object is preserved in a vault at Sevres,
France.

Work may be meaasured as force times distance or as pounds times feet.
Power is work per unit time. Power may be expressed as foot-pounds per
minute. James Watt`s horse was said capable of working at a rate of
33,000 foot-pounds per minute. I calculate that as 250 kilogram-feet per
second or 76.2 kilogram-meters per second.

Those aren't acceptable units in the modern metric system, however
(and it would actually be 76.0 kgf m/s, not 76.2).

BTW, Watt used the miner's measurements of mass as if they were
measurments of force in determining that a mine pony could do
sustained work at the rate of 22,000 foot-pounds per minute, before
using his arbitrary 1 horsepower = 1.5 ponypower conversion.

In the modern metric system, an English horsepower is 745.700 newton
meters per second, or 745.700 joules per second, or 745.700 watts.
Those pounds force convert to newtons, not to kilograms force, in SI.
The metric horsepower (PS in German acronym, CV in French acronym) is
75 kgf m/s, or 4500 kgf m/min. In SI, that's 735.4875 W.

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