Is gravity an inertial force or interaction force?

[Aeronautic Freek]

We feel that Earth pull as to the ground but is Earth accelaritng up "in some way" so gravity is also inertial force??
I read that we still don't understand what is gravity...

 

[Ibix]

Depends. In the Newtonian model, gravity is a true force. In relativity, "gravitational force" is an inertial force. Just like being in a car "being pressed into" your seat as you accelerate, you only feel a force because something is pressing into you and pushing you out of your inertial trajectory. That's why you can be weightless in a plane following a ballistic trajectory - look up the Vomit Comet if you haven't heard of that.

I believe at least one candidate for a quantum theory of gravity treats gravity as a true force, so the book is not yet closed.

 

[Dale]

We feel that Earth pull as to the ground but is Earth accelaritng up "in some way" so gravity is also inertial force??
I read that we still don't understand what is gravity...

Gravitational forces are a bit tricky. They share the following characteristics with inertial forces:

They cannot be detected by accelerometers
They are proportional to mass
They can be removed by changing reference frames

On the other hand gravitational forces share the following characteristic with interaction forces

They can follow Newton’s third law (they can conserve momentum)

I tend to still group them with inertial forces, but it isn’t a perfect match.

 

[vanhees71]

It depends on the accuracy you want to describe gravity. Gravity is equivalent to inertial forces in a limited region of space and time, over which the gravitational field can be assumed to be constant. Mathematically you can always find a reference frame, where at one point in space time you can describe locally everything as if there's no gravity and spacetime is described by Minkowski space. However, that's only true to the extent you don't look at higher accuracy for deviations, i.e., the socalled tidal forces, which occur on spacetime scales over which you cannot neglect to the given accuracy the inhomogeneity of the gravitational field. This manifests itself in a non-vanishing curvature of spacetime, i.e., you can approximate this curved spacetime only locally by a flat tangent space. That's analogous to the geometry on the earth. Only locally can you describe it by a flat Euclidean plane. As soon as you look over larger distances the curvature of the Earth becomes important for navigation.

 

[Aeronautic Freek]

Gravitational forces are a bit tricky. They share the following characteristics with inertial forces:

They cannot be detected by accelerometers
They are proportional to mass
They can be removed by changing reference frames

On the other hand gravitational forces share the following characteristic with interaction forces

They can follow Newton’s third law (they can conserve momentum)

I tend to still group them with inertial forces, but it isn’t a perfect match.

Do you have some animation how easier understand gravity with curved space time?
somethink like this..

 

[Ibix]

Do you have some animation how easier understand gravity with curved space time?

That "rubber sheet" picture is hopelessly misleading. xkcd puts it well.

Basically, no. There is no good animation of curved spacetime because any honest representation of a pseudo-Riemannian manifold needs a book-length explanation of how it should be interpreted. In other words, you need a textbook. And you need a textbook on special relativity before you even start on general relativity.

 

[vanhees71]

The only really intuitive experience with the curved pseudo-Riemannian spacetime is the action of the graviational interaction itself. There's not way to visualize it in an adequate way by curved surfaces in 3D space. Though shalt not make images (other than mathematical ones)!

 

[Dale]

Do you have some animation how easier understand gravity with curved space time?
somethink like this..

Our member @A.T. has some excellent animations, but it is not what you think from pop-science sources.

Are you familiar with space-time diagrams? You would need to understand those first.

 

[Aeronautic Freek]

Our member @A.T. has some excellent animations, but it is not what you think from pop-science sources.

Are you familiar with space-time diagrams? You would need to understand those first.

No I am not,also my physics basics is very poor..as everbody can see from my posts..

 

[A.T.]

Do you have some animation how easier understand gravity with curved space time?
somethink like this..