All Questions
Tagged with newtonian-gravity energy
17
questions
9
votes
1
answer
4k
views
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
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
views
Lagrangian potential for Newtonian gravity
In the Wikipedia site for Lagrangian (field theory) the Lagrangian density for Newtonian gravity is given by
$${\cal L}(\mathbf{x},t) = \frac{1}{2}\rho(\mathbf{x},t)\mathbf{v}^2 -\rho(\mathbf{x},t) \...
- 105
11
votes
4
answers
3k
views
Why does an orbit become hyperbolic when total orbital energy is positive?
I stumbled across this page describing the energy of a given object in orbit.
It describes 'total energy' as:
$$E_{k} + E_{p} = E_{\mathrm{total}} $$
where
$$E_k = \frac{1}{2}mv^2$$
and
$$E_p = \...
- 113
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
0
votes
2
answers
420
views
How much more net energy do I use walking up hill?
I have a question regarding work done / energy done.
Say a $70\mathrm{kg}$ man walked $100\mathrm{m}$ on a horizontal surface as a constant speed, is it correct to assume the energy done by this man ...
10
votes
3
answers
2k
views
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
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
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?
4
votes
1
answer
218
views
Double counting potentials in $N$-Body Problem?
I suspect an error in my “Classical Dynamics” lecture notes but my lecturer doesn’t agree with me so I need your help!
We assume that in the $n$-body problem, the force between particle $i$ and $j$ ...
- 145
4
votes
5
answers
4k
views
Climbing Stairs and Calories Burnt
I climb stairs to work (20 floors) every day . The least amount of work my body is doing by gaining potential energy (P.E) = mgh where m is mass , g is acc. due to gravity and h is height . Assuming ...
- 143
2
votes
1
answer
42k
views
Needed Energy For Lifting 200 kg weight
I'd like to learn how much energy I need to lift a 200 kilograms weight on normal earth conditions?
For example how much electric power do we need?
I'm not a physicist and not a student and this is ...
- 123
1
vote
3
answers
988
views
Potential energy and work-energy theorem
Let us suppose that a ball is present on earth's surface, gravity acts on it. Now if a force is applied on the ball in the opposite direction of gravity such that the applied force counters gravity ...
10
votes
1
answer
21k
views
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
614
views
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