What is inertia?

[bumab]

I always thought I knew... resistance to movement, or the reason force needs to be applied to accelerate someting.

 

Apparently it's not that simple, and like a two year old, I'm going to ask "why?"

 

This site has a longish explanation, which makes sense, but since contractory reports are all over the net (from valid sources) I was wondering if anyone here had any thoughts.

 

http://www.calphysics.org/inertia.html

[C1ay]

I always thought I knew... resistance to movement, or the reason force needs to be applied to accelerate someting.

It is more accurately described as the persistence of a body to remain in it's present state, be it rest or uniform motion.

[nkt]

I always thought I knew...

No-one knows. I think of it as an after effect of gravity.

 

I think that gravity, though the weakest of the four forces, is the only one which distorts the "fabric" of the universe, due to some interaction with matter, what we call mass. This is obvious when you think that inertia and mass exist in freefall, but weight means nothing.

 

Higher gravity areas distort the fabric more than low or zero gravity areas, and you can think of these as being the same thing - gravity being higher is due to the fabric being more sloped "towards" the mass doing the distorting. This is what most people think of when they see a picture of a star and the planets moving round it.

 

Inertia could well be thought of as the drag that the mass of the object exerts on that fabric of space-time.

 

< my theory>

And very like a neutral conductor in a static electric or magnetic field, the force applied to the object is only there when a force/acceleration is applied, and it acts to prevent that change, as eddy currents act against the force on the conductor.

 

The difference is obvious, though, in that once moving, there are no more "eddy currents" in the inertia/gravity side of things, so the object is not brought back to rest, and, in fact, the opposite happens, and when you want to slow the object, you again have to overcome that same drag.

 

A test on the level of inertia experienced far out of the earth's (and sun's?) gravity well would perhaps shed some light on this. It could explain a lot of things.

</my theory>

[bumab]

It is more accurately described as the persistence of a body to remain in it's present state, be it rest or uniform motion.

 

Yes, I was being vauge. But why? Why does mass possess the property of persistence, and is resistant to movement?

 

I don't think there's an answer as of yet. Looking around, I've found many things related which refer to the Higgs field, but nothing definitive. Just looking for any new theories i've not seen.

[Qfwfq]

Why does mass possess the property of persistence, and is resistant to movement?

Because, just think how odd the universe would be, otherwise!

 

The first thing Nkt said is quite right: Nobody knows...

 

The second thing was proposed by Mach quite some time ago.

 

Looking around, I've found many things related which refer to the Higgs field, but nothing definitive.

The Higgs boson in the standard model determines what mass each particle has, as usual in terms of "more fundamental" things including Higgs' own huge mass. This is a slightly different thing from saying why things have mass and yet different from saying why something that has mass has inertia.

 

First: from a perspective of 20th century physics it's better to say that energy has inertia.

 

For any given Lagragian or Hamiltonian, there is a relation between force and motion which determines the law such as Newton's third. Why things should have a Lagrangian and Hamiltonian of a certain form is, again, hacking away at the metaphysical.

 

Just looking for any new theories i've not seen.

Personally, I haven't seen or heard of any others.

[UncleAl]

Stochastic electrodynamics is stillborn to date. Apeals to Unruh radiation as the source of reactive force of inertia were discredited by Unruh. SED cannot produce the Schroedinger equation. SED is only mathematics and philosophy until it can produce some results - novel predictions vs. observations or even basic physical theory.