On Sun, 14 Dec 2003 at 13:08:32 in message
, Peter Duniho
wrote:
"David CL Francis" wrote in message
...
Its mass is the same; its weight differs. You are still being confused
between weight and mass.

It is true that its weight differs. It's farther from the Earth's center of
gravity, thus the weight is necessarily less. However, I think what Jeffrey
was trying to point out is that the satellite still does *weigh* something.
And in fact, its weight is almost as great as it would be sitting on the
surface of the Earth.

That is mass you are talking about. I defined weight earlier. But why
'almost' in your world?

Weight is the measure that you find if you weigh something on a spring
balance.

I think this view of "weight" is what's tripping you up. The satellite in
freefall would appear to weigh nothing if weighed on a weighing scale that
is also in freefall with the satellite. However, that doesn't mean that the
satellite weighs nothing. In fact, if it weren't for its weight, it would
fly off at a tangent to its orbit.


It is not a 'view' it is definition to help to try and help you
understand the difference between force and mass. I am not the list bit
'tripped up'.

The satellite's weight is what keeps it in orbit. It's just not true that
the satellite weighs zero in orbit. It's my impression that this is what
Jeffrey was saying in his post.

Once more, it is the satellite's MASS that keeps it in orbit and the
MASS of the earth..

Mass is a measure of the total quantity of matter in an object. If you
are floating in deep space in free fall, then you cannot detect any
weight.

Detecting weight and the existence of weight are two different things.
Consider the folks riding the "Vomit Comet", the jet used to create freefall
conditions without going into orbit. The occupants of the aircraft during
its parabolic flight cannot detect their weight. However, it is their very
weight that keeps them accelerating toward the planet, as it always does
during the non-parablic phases of flight or even while standing on solid
ground.

You are talking mass again. Weight is a force, Mass is the _quantity_ of
material in an object.

However the _mass_ is the same and if a force (perhaps from a
rocket motor} is applied then the acceleration depends on the force
exerted by the rocket and the mass of the object.

I'm not sure what this has to do with the so-called "weightless satellite".


Some of the confusion arises because in the imperial system of units
there is no obvious distinction in the measurement of them.

I'm not sure that explains your confusion regarding whether a satellite in
orbit is weightless or not.

For the last time - I am not confused.

For ordinary everyday, stuck on the surface of earth, people the
distinction is subtle. To engineers, physicists and applied
mathematicians the distinction is essential.

Which is why it's odd you seem to think that a satellite in orbit is
weightless. It's not.

I give up. Get a book on physics or applied mechanics. Perhaps someone
else might be able to help. You seem to be stuck with your preconceived
idea as to what weight and mass are, or to put it another way as to what
a force and a mass are.

If I mention that force is a vector quantity (weight is a force) and
that mass is a scalar quantity, I suppose that will mean nothing to you?

A quote from an A level physics book:
~~~~~~begin quote~~~~~~~~~~
The weight of a body is the force of gravity acting on it towards the
centre of the earth. Weight is thus a _force_ , not to be confused with
mass which is independent of the presence or absence of the earth.
~~~~~~~~~~~~~end quote~~~~~

The Gravitational force F between two particles of masses m1 and m2 , a
distance r apart ,is given by;

F=(G*m1*m2)/r^2 where G is the Gravitational constant.
--
David CL Francis