All Questions
16
questions
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What is the difference between GPE and gravitational self energy in GR?
What is the difference between gravitational potential energy and gravitational self energy in General Relativity? Are they both the same in Newtonian gravity?
- 476
1
vote
1
answer
93
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Some questions regarding graviational potential energy and the concept of potential energy in general
Starting off, I first want to know the relation between work and potential energy.
$\Delta\mathbf U = - W $
How was this expression formulated?
Moving on,
My second doubt was in the derivation of the ...
- 82
0
votes
1
answer
32
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What are the Gravitational PE conventions for setting the zero point at infinity?
If you set the zero point at infinity (the edge of the universe), is the gravitational PE still zero at a distance $\infty \pm r$? Or would you make it a $0 \pm (-Gm_1 m_2/r)$? Basically, is infinity ...
- 65
-1
votes
3
answers
194
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Can gravitation violate the law of conservation of energy? (Boils down to: Why is the force of gravity assigned a negative value?)
I guess it can't, but here is the idea:
Let's consider a massive object with mass $M$. Then we have another object with a way smaller mass $m$. Now, the smaller object is a distance $r$ away. The ...
- 103
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2
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51
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Simplified formula of potential energy giving different expected value of mass
I am trying to calculate the mass of a planet by the following image
I have the mass of the object, $2$ kg, and the radius of the planet, $5000$ km (also the gravitational constant $G$).
My first ...
- 105
0
votes
3
answers
451
views
How does an object gain energy when it enters a potential field?
Conservation of energy says total change in energy is $0$.
Let's assume a small object is in outer space (maybe like a football).
It moves towards a planet (assume planet has no atmosphere for ...
7
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2
answers
1k
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What is the physical reason for why gravitational potential (or electrical potential) due to two masses at a point can simply be added algebraically?
The simple explanation that textbooks and the internet say is that "gravitional potential is a scalar quantity hence can be added algebraically".
However, I'm not sure if it is that simple. Take for ...
- 797
0
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1
answer
546
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How do I calculate the actual gravitational potential energy between two objects $m_1$ $m_2$ that are at zero distance?
How do I calculate the gravitational potential energy between two objects that are separated by near to infinite distance? I would like to know if the two objects are kept at near infinite distance, ...
- 109
12
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2
answers
22k
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Gravitational potential energy of any spherical distribution
The general formula to get the potential energy of any spherical distribution is this :
\begin{equation}\tag{1}
U = - \int_0^R \frac{GM(r)}{r} \, \rho(r) \, 4 \pi r^2 \, dr,
\end{equation}
where $M(r)$...
- 7,592
0
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0
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143
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Deriving Kepler's First Law from Newton's Law of Universal Gravitation: Interpretation of the $u = 1/r$ change of variable
I'm working through a somewhat unsatisfying derivation of Kepler's First Law from Newton's Law of Universal Gravitation. The key to obtaining the equation of motion that you can solve lies in making ...
- 259
3
votes
4
answers
279
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How do I correctly introduce time into this equation?
So, for the past few years it's been my goal to create an equation that would give me the position of an object in a gravitational field at time $t$, given it's initial position and velocity. At first ...
- 145
0
votes
2
answers
433
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Why is the potential energy for a body raised up by a height negative?
I tried deriving the potential energy of a body when raised at a height $h$ above the earths surface, using the formula:
$$PE = -W_\text{conservative}$$
where $W_\text{conservative}$ is the work ...
0
votes
1
answer
182
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Is there anything interesting about an n-body system whose potential energy is constant?
I am curious about a system of gravitating bodies with particular characteristics. Before describing the characteristics of the system, let me say what I want to know about it:
Can this be a ...
- 1,517
4
votes
3
answers
7k
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Still trying to understand gravitational potential and Poisson's equation?
A week or so back I asked a question about the gravitational potential field
$$\phi=\frac{-Gm}{r}, \qquad r\neq 0, $$
and how to show the Laplacian of $\phi$ equals zero for $r\neq 0$? Eventually, (...
- 3,059
2
votes
2
answers
1k
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Why no basis vector in Newtonian gravitational vector field?
In my textbook, the gravitational field is given by$$\mathbf{g}\left(\mathbf{r}\right)=-G\frac{M}{\left|\mathbf{r}\right|^{2}}e_{r}$$
which is a vector field. On the same page, it is also given as a ...
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