Equivalence principle to other forces?

[Gerenuk]

Why is it that to derive general relativity you use the equivalence principle on gravity and not electromagnetism for example?

 

[Al68]

Why is it that to derive general relativity you use the equivalence principle on gravity and not electromagnetism for example?

Because the equivalence principle would be obviously false if applied to electromagnetism instead of gravity.

 

[Gerenuk]

That's a "Becauso so." answer

Electromagnetism is a force and acceleration exhibits a force. So at least from the basic ideas that I heard it doesn't make a difference.

 

[Nabeshin]

Gravitational mass and inertial mass are the same.

What equivalent statement could you possibly make about any of the other forces?

 

[Gerenuk]

I see. I was thinking about the force argument only. I have the feeling that's a good answer.

And I cannot apply the same concept to electric charge? (converting the units appropriately)

 

[Al68]

That's a "Becauso so." answer

Electromagnetism is a force and acceleration exhibits a force. So at least from the basic ideas that I heard it doesn't make a difference.

I don't know what a "Becauso so." answer is, but the "force" of electromagnetism isn't equivalent to a pseudoforce in accelerated reference frames the way gravitational "force" is.

The "basic idea" of the equivalence principle isn't about forces being equivalent, they generally aren't. It's about the equivalence of reference frames. Two accelerated reference frames are equivalent if the only difference between them is the presence of a gravitational field. No local experiment can even detect the presence of the gravitational field. In both cases a ball thrown "up" will "fall", for example. The ball "falls" because of the acceleration of the reference frame, not because of a real force.

An electromagnetic field can easily be detected by local experiments, so the equivalence principle is not valid for electromagnetism.

 

[DrGreg]

Why is it that to derive general relativity you use the equivalence principle on gravity and not electromagnetism for example?

I think you've more or less worked this out now. In Newtonian terminology, the "acceleration due to gravity" of a particle does not depend on the particle's mass (or any other property of the particle). The "acceleration due to electromagnetism" depends on the particle's charge-to-mass ratio.