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Hi!

I'm a real noob in physics, so to say in modern international language. I just got interested in it by starting to read Feynman's lectures on physics. So after reading a several dozen pages, collecting back much of the basic knowledge I threw out of my mind after school, spiced up with Feynman's insightful comprehensive way of explaining and putting it all together, it got me really intrigued and fascinated. But together with this forgotten knowledge and interest came back also some old questions that are bugging me. My English may be a bit buggy, too. I hope you will understand me anyway :)

First question: What is potential energy? Is potential energy always defined in terms of an arbitrarily chosen reference point? For example: The potential energy in the earth's gravitational field is _defined_ to be zero for a mass that is placed on the earth's surface and more than zero for a mass placed somewhere above in the sky, but it could be defined in another way, the difference from the other definition being a constant? Or is it the case that in fact there is a _canonic_ reference point (the earth's mass center that would be probably)?

If the first was the case it would bug me for the following reason: According to the theory of relativity mass is equivalent to energy, and energy, just as mass, causes gravitation. So what about potential energy? If we can define it this or that way things are spoiled. And, second, _where_ is the potential energy? A source of gravitation should be located somewhere. So, is the center of gravitation caused by the potential energy at the potential's zero point?

If, on the other side, the potential's zero is located at the mass center of the earth any other position would have a potential energy of infinity because it would take an infinite amount of energy (E=GMm(1/r_0-1/r) with 1/r_0 being infinity) to move a mass from the center of the gravitational field to somewhere else, wouldn't it?

As you may critizize I talked about the theory of relativity and am still using a classical formula for the potential energy of the gravitational field. That's because I don't know the relativistic formulae, and I hope that my question is not totally led ad absurdum by that.

The second question: I forgot. :(

So, I hope someone can answer this question that already got me suspicious towards physics back when I was at school among other things that I forgot. I'm really curious.

Sincerely

Unkraut

I'm a real noob in physics, so to say in modern international language. I just got interested in it by starting to read Feynman's lectures on physics. So after reading a several dozen pages, collecting back much of the basic knowledge I threw out of my mind after school, spiced up with Feynman's insightful comprehensive way of explaining and putting it all together, it got me really intrigued and fascinated. But together with this forgotten knowledge and interest came back also some old questions that are bugging me. My English may be a bit buggy, too. I hope you will understand me anyway :)

First question: What is potential energy? Is potential energy always defined in terms of an arbitrarily chosen reference point? For example: The potential energy in the earth's gravitational field is _defined_ to be zero for a mass that is placed on the earth's surface and more than zero for a mass placed somewhere above in the sky, but it could be defined in another way, the difference from the other definition being a constant? Or is it the case that in fact there is a _canonic_ reference point (the earth's mass center that would be probably)?

If the first was the case it would bug me for the following reason: According to the theory of relativity mass is equivalent to energy, and energy, just as mass, causes gravitation. So what about potential energy? If we can define it this or that way things are spoiled. And, second, _where_ is the potential energy? A source of gravitation should be located somewhere. So, is the center of gravitation caused by the potential energy at the potential's zero point?

If, on the other side, the potential's zero is located at the mass center of the earth any other position would have a potential energy of infinity because it would take an infinite amount of energy (E=GMm(1/r_0-1/r) with 1/r_0 being infinity) to move a mass from the center of the gravitational field to somewhere else, wouldn't it?

As you may critizize I talked about the theory of relativity and am still using a classical formula for the potential energy of the gravitational field. That's because I don't know the relativistic formulae, and I hope that my question is not totally led ad absurdum by that.

The second question: I forgot. :(

So, I hope someone can answer this question that already got me suspicious towards physics back when I was at school among other things that I forgot. I'm really curious.

Sincerely

Unkraut

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