B What kind of force acts in the center of the Earth?

[Gabriele Pinna]

What kind of force acts in the centre of the Earth ? What is the intensity ?

 

[BvU]

There is quite some pressure there and it is pretty hot as well.

 

[Svein]

And, of course, the force from the sun according to Newton's law (and from several other celestial bodies...).

 

[Gabriele Pinna]

What about the gravitational force acts by the Earth ?

 

[Doc Al]

What about the gravitational force acts by the Earth ?

If you assume the Earth has a spherically symmetric mass distribution, the gravitational force of the Earth on an object at the center of the Earth would be zero.

 

[ProfuselyQuarky]

Could you say normal force is acting on the center, or no?

 

[A.T.]

Could you say normal force is acting on the center, or no?

Normal to what?

 

[ProfuselyQuarky]

Normal force meaning any force acting on something at a $90^{\circ}$ (right) angle. If we’re talking about a single point in the center of the earth, would that mean that normal force is acting on the point in all directions?

 

[Doc Al]

Could you say normal force is acting on the center, or no?

A "normal" force is usually a force between an object and some supporting surface (and normal to that surface). What did you have in mind?

 

[ProfuselyQuarky]

and normal to that surface

Normal meaning orthogonal. I didn’t know there had to be a supporting surface.

If we’re talking about a single point in the center of the earth, would that mean that normal force is acting on the point in all directions?

I had that in mind. I was wondering if that was correct or incorrect. I guess it's incorrect?

 

[mfb]

Normal force meaning any force acting on something at a $90^{\circ}$ (right) angle. If we’re talking about a single point in the center of the earth, would that mean that normal force is acting on the point in all directions?

90 degree angle relative to what? Any direction looks the same, there is no normal force because the concept does not even make sense.
And a force from what?

 

[A.T.]

would that mean that normal force is acting on the point in all directions?

That is pressure in a fluid, not normal force.

 

[ProfuselyQuarky]

90 degree angle relative to what?

That’s what I was asking about. Since the 90 degrees would not be relative to any specific surface, I thought that would mean that the force could be acting on the point in all directions.

the concept does not even make sense.

Okay, fine. The idea is jargon.

That is pressure in a fluid, not normal force.

I see . . . thanks for the explanation :)

 

[BvU]

What about the gravitational force acts by the Earth ?

I figured that's what you were really inquiring about -- and teasingly avoided that in my first answer. The Doc made good on that, but perhaps it's good to elaborate a bit more. For $1/r^2$ laws such as Newton's law of gravity ( and following ) and Coulomb's law one can derive Gauss' theorem that popularly says: you only have to take into account what's underneath you -- the contributions from the part of the sphere with a greater distance to the center cancel.

And it makes sense: along a hole through the Earth something has to happen with the force from gravity, because at the other end it has the same magnitude but points the opposite way.