Accurate plane performace?

"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.

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.

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.

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.

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 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.

Pete