Energy and Work Energy and Work Physics Help Forum  4Likes
Aug 2nd 2019, 03:03 AM

#1  Junior Member
Join Date: Aug 2019
Posts: 2
 Definition of Gravitational Potential Energy
Can anyone explain to me the definition of gravitational potential energy? I mean, i understand that it is 'the total work done in bringing a mass from infinity to the point' for any mass at a point, but it just seems too vague. For instance, why is it zero at infinity and negative nearer to the gravitational body?
and why do we have to start counting from infinity, not from the gravitational body itself?

 
Aug 2nd 2019, 05:32 AM

#2  Senior Member
Join Date: Aug 2010
Posts: 434

"Potential" anything is a function whose derivative is that anything. That is, "potential energy" is the antiderivative of the energy function. An antiderivative always involves an arbitrary constant. For potential energy, it is purely a convention that the arbitrary constant is set by taking potential energy to be 0 "at infinity".

 
Aug 2nd 2019, 06:16 AM

#3  Senior Member
Join Date: Apr 2017
Posts: 513

Originally Posted by HallsofIvy For potential energy, it is purely a convention that the arbitrary constant is set by taking potential energy to be 0 "at infinity". 
I'm not sure that's correct ....
Suppose there are only two masses in the Universe . The condition of maximum potential energy is when they are infinity apart ...
Minimum potential energy is when their centers of mass coincide.

 
Aug 2nd 2019, 07:51 AM

#4  Senior Member
Join Date: Jun 2016 Location: England
Posts: 1,069

I agree Oz,
it does seem a totally backwards convention to use,
But HallsofIvy usually knows what he is posting about
and it wont be the only bizarre and totally counterintuitive convention I have encountered.
Sometimes it seems that the "oldtimers" who initially set these conventions were being deliberately contrary.
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Aug 2nd 2019, 04:39 PM

#5  Senior Member
Join Date: Mar 2019 Location: cosmos
Posts: 666
 positive vs negative
Actually, we can start from the infinite or the center of the gravitatioal body. It's only the difference between negative and positive values. If we start from the infinite, we can get an approximate feasible way to set out. If we start form the center of the gravitational body, we set out from a nearly impossible mission. In another hand, in the infinite the gravity is zero, if we take potential energy is also zero, then we feel more natural in logic.

 
Aug 2nd 2019, 05:46 PM

#6  Forum Admin
Join Date: Apr 2008 Location: On the dance floor, baby!
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Just to put my four cents worth (two cents worth + inflation):
There are many points to use to talk about a 0 potential energy for any system. I've seen GPE set at the Earth's surface, at it's core, at the Sun, and out at infinity. I think that the best answer is a blend of Oz and HallsofIvys concepts. It's like finding the sum torques on a system of forces... You just pick one that's useful. (I do agree with HallsofIvy when he gave the Mathematical definition of a PE. There's nothing for me to add to that.)
Dan
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Aug 2nd 2019, 06:54 PM

#7  Senior Member
Join Date: Mar 2019 Location: cosmos
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 cent vs cent
In APPLICATION the zero point of GPE could even set on the toe of that dragon. But I would rather to think about the DEFINITION in pure physics.
GPE is the experience of the difference of "curvature of space time". In the infinity, space time is "flat" (no curvature). So, the zero point of GPE defined in the infinity is reasonable in physics and nature. Non cent vs Non cent. FAIR.

 
Aug 2nd 2019, 07:01 PM

#8  Forum Admin
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Originally Posted by neila9876 In APPLICATION the zero point of GPE could even set on the toe of that dragon. But I would rather to think about the DEFINITION in pure physics.
GPE is the experience of the difference of "curvature of space time". In the infinity, space time is "flat" (no curvature). So, the zero point of GPE defined in the infinity is reasonable in physics and nature. Non cent vs Non cent. FAIR. 
No offence intended but I have a feeling that General Relativity is a little too abstract at the level of HS.
Dan
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Aug 2nd 2019, 07:33 PM

#9  Senior Member
Join Date: Mar 2019 Location: cosmos
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@dragon:
Oh...

 
Aug 5th 2019, 02:54 AM

#10  Senior Member
Join Date: Oct 2017 Location: Glasgow
Posts: 474

Originally Posted by topsquark Just to put my four cents worth (two cents worth + inflation):
There are many points to use to talk about a 0 potential energy for any system. I've seen GPE set at the Earth's surface, at it's core, at the Sun, and out at infinity. I think that the best answer is a blend of Oz and HallsofIvys concepts. It's like finding the sum torques on a system of forces... You just pick one that's useful. (I do agree with HallsofIvy when he gave the Mathematical definition of a PE. There's nothing for me to add to that.)
Dan 
This is exactly what we do in practise. Once a convenient fiducial value is identified and adopted by practitioners, it usually leads to a convention or standard reference value. A good example is the Rydberg energy.

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