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Re: Constraint and inertia



Is the speed used to calculate kinetic energy the same as speed used
to calculate a distance in kinematics? Yes. Why? Because we use
F=m*a to derive the "Work Kinetic Energy Theorem" and to give
a name to the quantity 0.5*m*v^2.

The mass and the inertia are not derived from each other and in that
sense they are two different physical quantities. It turns out however,
that they are identical in most cases, both numerically and dimensionally.
When are they not identical, Leigh? Which of them should we think
about while using the E=m*c^2 formula? My tentative answer would
be inertia, not the mass. Why? Because special relativity is kinematics.
Ludwik Kowalski

Joel Rauber wrote:

I can't resist commenting. Does the below mean that Leigh and the other
anonymous author believe that the concept of "coefficient of inertia" and
"'mass'" in terms of its "gravitational effect" are indeed different
concepts.

Leigh Palmer wrote:

Mass is the coefficient of inertia. It expresses the strength
of the tendency to "preserve velocity" quantitatively. "Mass"
has another function, its gravitational effect. Thus "inertia"
refers only to one attribute of mass. The terms are not
interchangeable in all contexts.

Was Newton aware that a "material object" has two attributes:
inertia, which appears in F=m*a, and mass, which appears in
the law of universal gravitation? Probably not. Who was the
first to make a clear distinction, and to show experimentally
that under common conditions the two physical quantities
(attributes) are identical?

In teaching we take the identity of mass and inertia for granted
when the mass of our planet is deduced from Cavendish data,
and from the value of g.