All Questions
Tagged with newtonian-gravity energy
125
questions
31
votes
4
answers
7k
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Why aren't the energy levels of the Earth quantized?
The Hamiltonian of the Earth in the gravity field of the Sun is the same as that of the electron in the hydrogen atom (besides some constants), so why are the energy levels of the Earth not quantized?...
- 1,523
15
votes
3
answers
5k
views
Is it possible to convert gravitational energy directly into electrical energy?
It is possible to produce strong gravitational accelerations on the free electrons of a conductor in order to obtain electrical current. This allows the conversion of gravitational energy directly ...
- 1,070
12
votes
5
answers
9k
views
How much energy do you need to levitate/counteract gravity without any displacement or change in height?
I know you can't have work without any displacement, so I was kind of wondering as to what keeps, for example, a man on a jetpack, off the ground but with no more change in height from the initial ...
- 123
12
votes
5
answers
2k
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Why is cycling easier while standing on the pedals?
On high slopes and rugged terrains, riding a bicycle while standing on the pedals is easier. Even though I cannot physically define what is "easy"; since it is a feeling that my body ...
- 12.5k
11
votes
4
answers
3k
views
Why does an orbit become hyperbolic when total orbital energy is positive?
I stumbled across this page describing the energy of a given object in orbit.
It describes 'total energy' as:
$$E_{k} + E_{p} = E_{\mathrm{total}} $$
where
$$E_k = \frac{1}{2}mv^2$$
and
$$E_p = \...
- 113
10
votes
3
answers
2k
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Under which conditions do two moving bodies start orbiting each other around their center of mass?
If two bodies are close, both will get attracted to each other and collide. Under what conditions will the two bodies start revolving around their common center of mass? I understand that such bodies ...
- 415
10
votes
1
answer
21k
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How much energy would it take to blow up the Earth?
There is a common statement running around that we as a species has enough nuclear weapons to blow up the earth several times over. What I want to know is: by how many orders of magnitude is that a ...
- 203
9
votes
1
answer
4k
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Feynman Lectures: Why a non-reversible weight lifting machine cannot lift higher that a reversible one?
Consider weight-lifting machines—machines which have the property that they lift one weight by lowering another. Let us also make a hypothesis: that there is no such thing as perpetual motion with ...
- 2,983
9
votes
1
answer
614
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Marvin the Martian vs. the Death Star: how much energy will they actually need to disintegrate the Earth?
According to a detailed analysis by Dave Typinski, Marvin the Martian’s Illudium Q-36 Explosive Space Modulator will require $1.711 \cdot 10^{32}~\text{J}$ to shatter the Earth into a gravitationally ...
- 360
8
votes
6
answers
16k
views
Why is potential energy negative when orbiting in a gravitational field?
I had to do a problem, and part of it was to find the mechanical energy of satellite orbiting around mars, and I had all of the information I needed. I thought the total mechanical energy would be the ...
- 2,889
7
votes
2
answers
3k
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Lagrangian potential for Newtonian gravity
In the Wikipedia site for Lagrangian (field theory) the Lagrangian density for Newtonian gravity is given by
$${\cal L}(\mathbf{x},t) = \frac{1}{2}\rho(\mathbf{x},t)\mathbf{v}^2 -\rho(\mathbf{x},t) \...
- 105
7
votes
3
answers
1k
views
How is gravitational potential energy $mgh$?
I know the derivation that $W=Fd$, hence $F=mg$ and $d=h$ so energy gained by the body is $mgh$ considering the body on the ground to have $0$ gravitational potential energy.
But the definition of ...
- 1,168
6
votes
1
answer
4k
views
Why doesn't the potential energy of any object equal 0
Consider a particle on the ground. This particle is raised by a force of magnitude $mg$ to a height $h$ above the ground. At this point, the work done on the particle by the force is $mgh$, which is ...
- 2,780
5
votes
2
answers
227
views
Positive and Negative works [duplicate]
When we displace a body from ground to a height we do positive work against gravity and gravity too does work but negative. Do they cancel each other? Or does the external force do extra work?
5
votes
6
answers
6k
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From where does gravity get its energy to do work upon an object?
For an object or force to do work, it needs energy. But, from where does the gravitational force get the energy to do work upon, say, a falling object? The gravitational force is doing work upon the ...
- 185