So you know what inertia is then Pete

I've actually seen different definitions for it, as it been bothering me for a while.

Here's one good.

" Mass has two meanings, both of which can be viewed as proportionality

factors. "Inertial mass" is the factor that determines how much force

it takes to produce a given acceleration in an object, according to

Newton's first law of motion:

F = ma

"Gravitational mass" is the factor that determines how much

gravitational force is developed between two objects at a given

distance, according to Newton's law of gravity:

F = -GMm/r^2

where G is the gravitational constant, r is the distance between the

objects, and M and m are the masses of the two objects.

Inertial mass and gravitational mass are the same. (This is still the

subject of experiments seeking to verify it more and more precisely,

because it is intimately connected with Einstein's general theory of

relativity.) Because of this, the two equations above combine into

a = GM/r^2

On the surface of the earth, M (the mass of the earth) and r (the

radius of the earth) are fixed, and so a (the acceleration due to

gravity) is a constant, which we call g."

From

Doctor Rick, mathforum.org So according to this inertia is equivalent to (rest) mass, as I read it?

If I use that definition then what we have in different uniform motions as I try to stop a object moving relative me is not its inertia, as that will differ relative the perceived 'speed'. Against it we have the fact that no matter your uniform motion (in space) you should expend the same amount of energy in a acceleration, or 'displacement' if you like, to start to move relative whatever frame you earlier found yourself being still relative.

Well, as I think of it.

In relativity "All inertial frames are in a state of constant, rectilinear motion with respect to one another; they are not accelerating in the sense that an accelerometer at rest in one would detect zero acceleration. Measurements in one inertial frame can be converted to measurements in another by a simple transformation (the Galilean transformation in Newtonian physics and the Lorentz transformation in special relativity).

In general relativity, in any region small enough for the curvature of spacetime to be negligible one can find a set of inertial frames that approximately describe that region."

This contains several ideas that makes sense, but inertia boggles me mind

And then you have

its mass, which governs its resistance to the action of a force, and its moment of inertia about a specified axis, which measures its resistance to the action of a torque about the same axis. with accompanying math from PF

as well as the definition of 'Moment of Inertia' in engineering.

And your definition too. All of them seems sort of valid to me? But then again, none of them touches uniform motion and what I should call that 'resistance' to 'stopping' as I apply a 'force' to make that object stand still relative me. As I see all uniform motion to be the same, as can be proved by accelerating something from a 'inertial frame' where its 'relative motion', meaning that 'inertial frames' uniform motion through space, doesn't matter.

=

Sorry, had to add some text above to make the citation more understandable. As well as a link to that very nice and concise first citation.