All Questions
Tagged with gravity reference-frames
103
questions
-1
votes
3
answers
101
views
Can two particles ever be in equilibrium under their mutual gravitational forces alone?
Can two particles be in equilibrium under the influence of their mutual gravitational forces alone?
Obviously, if the two particles are kept at rest at a distance apart, one will exert an attractive ...
- 11.7k
8
votes
5
answers
1k
views
Do you always experience the gravitational influence of other mass as you see them in your frame?
You see a galaxy far away. That galaxy is attracting you with a certain amount of gravity. I'm wondering if the gravity influence of the galaxy on you, as measured by you, always ends up being what ...
- 171
3
votes
2
answers
86
views
Tug of war between observers in frames with different rate of time
You have a very dense hollow sphere of matter. Observer A is inside the sphere inside a rocket. Observer B is in an identical rocket outside the sphere where the ring's gravity is negligible. They are ...
- 171
3
votes
2
answers
85
views
How is it that energy of matter yields gravity if the amount of energy in a system is frame dependent while the force caused by gravity is not?
I've been told that the gravitational field arises due to the energy density terms in the stress-energy tensor of matter and therefore that all energy of matter exerts a gravitational field effect, ...
- 531
4
votes
5
answers
262
views
How is Gravity, assuming only General Relativity, *not* like Centrifugal Force?
It is common to state that "Gravity is not a force" due to its interpretation as a curvature effect in general relativity. By this, is it right to say that gravity is a fictitious force due ...
0
votes
0
answers
28
views
When we are on the ground do we still accelerate with 9.8 m/s²? [duplicate]
Do we accelerate with 9.8 m/s² when we are on the ground , if so why we do not fall inside the eart . How is the net force is zero , how many real forces acts on the body ?
- 1
1
vote
0
answers
27
views
Fictitious forces and the Unruh effect
Here is a (practically infeasible) method to determine whether you are in a non-inertial frame of reference:
Look around you, and calculate all of the forces acting on you. The piece of lint on the ...
- 179
-2
votes
1
answer
139
views
If time moves slower the faster you go. Doesn't that mean that the gravity experienced will be lower too?
Disclaimer: I still don't understand the theory of general relativity. I'm completely ignorant.
I was watching the movie Interstellar yesterday and saw their interpretation of time dilation, I also ...
- 127
3
votes
1
answer
117
views
Transformation of derivatives of coordinates
I am quite new to this topic. Please bear with me.
Suppose we are given a transformation of both time and space coordinate's derivatives as
$$
\partial_t\to D_t=\partial_t-f(t,x)\partial_t\\
\nabla\to ...
- 1,335
2
votes
2
answers
2k
views
What kind of coordinate change is needed to make gravity disappear?
I understand that the Christoffel symbols associated with the metric will vanish locally once you perform the appropiate change of coordinates. These new coordinates correspond to an observer in free-...
- 391
4
votes
2
answers
371
views
Are objects in an uniform field inertial?
It is currently understood that gravity is not actually a force, and a fact that is often used to show this is that an object in free fall doesn't "feel" that it is accelerating and is thus ...
- 365
2
votes
2
answers
102
views
More on frames of reference and coordinates in GR
I have read other questions concerning this subject, and by now I believe that in order to solve a gravitational problem in GR, one has to basically abandon the notion of frames of reference. However, ...
- 307
25
votes
4
answers
7k
views
If gravity is not a force, then how come gravitational assists work?
I have learned about general relativity and how gravity arises from spacetime curvature. And I have always been taught that gravity is not a real force in the sense that
$$\frac{dp}{dt} = 0$$
And from ...
- 1,896
2
votes
2
answers
119
views
Does a linearly accelerated observer inside an inertial spherical charged shell detect an electric field?
The electric field inside a charged spherical shell moving inertially is, per Gauss's law, zero.
If the spherical shell is accelerated, the field inside is not zero anymore, but it gains a non-null ...
- 133
-2
votes
1
answer
243
views
A problem in the light beam experiment of the equivalence principle?
Could someone tell me where i'm wrong? The light beam experiment of the equivalence principle which was the mind experiment that made Einstein deduce the curvature of light around heavy objects, has a ...
user348262
2
votes
3
answers
184
views
Weight in Interplanetary Space
How is weight zero in interplanetary
space? The Moon is orbiting the Earth because of the gravitational pull of earth. Then gravity must exist in interplanetary space too. So any body in space must ...
- 19
1
vote
0
answers
117
views
Is the generating function the phase factor when transforming from inertial to non-inertial coordinates?
Question
When going from the Hamiltonian of an inertial frame $H$ to that of a non-inertial frame $H'$ they are related by the canonical transformation:
$$ H = H' + \frac{\partial F}{\partial t}$$
I ...
- 1,389
0
votes
1
answer
77
views
Defining acceleration in gravity-free space
Without information from outside a closed spaceship, an astronaut cannot distinguish A from B.
A) In gravity-free space, the floor accelerates upwards at $a=g$ and hits a dropped watch.
B) On earth's ...
- 65
0
votes
0
answers
43
views
Using position of a free particle to measure time
Hartle, gravity
An observer in an inertial frame can discover a parameter t with
respect to which the positions of all free particles are changing at constant rates.
This is time
Then goes on to say
...
- 1,270
1
vote
3
answers
165
views
Does Mach's principle imply that the gravitational field has a non-zero curl?
I would normally visualize the gravitational field as "radial", i.e., one whose curl is zero. However, while thinking about Mach's principle, particularly the notion of frame-dragging (as ...
- 1,325
2
votes
0
answers
58
views
Is there a way to know if you accelerate in empty space or in a uniform gravitational field?
If I'm in a room that accelerates through empty space uniformly I won't measure tidal forces. The situation is the same as standing on an infinite massive plane. So I could think, while looking ...
2
votes
2
answers
213
views
Why are there so many fundamental differences between contact forces and gravity?
I had this very fruitful conversation about the inertial motion of charged particles on gravitational/electric fields.
A field force like gravity, can't be felt, it does not produce proper ...
- 350
0
votes
1
answer
283
views
How can a person inside from a veiled and free-falling elevator distinguish whether he is in an inertial or non-inertial frame?
From wikipedia: "A non-inertial reference frame is a frame of reference that undergoes acceleration with respect to an inertial frame", according to that statement, I would say that an ...
- 339
2
votes
1
answer
198
views
Does an accelerated frame of reference have the same effect as that of mass in space time
According to the equivalence principle, gravity and inertial forces are similar. And according to general Relativity, If there’s a large object in space-time, it warps the space time’s geometry and ...
- 131
0
votes
2
answers
330
views
Earth as inertial reference frame: finite radius effects
In a recent question I tried to clarify under what conditions the Earth can be considered as an inertial reference frame. The opinions, summarized in my own answer to the cited question, are that
...
- 60.4k
10
votes
9
answers
4k
views
Why and when can the Earth be considered an inertial reference frame?
The question has been asked (e.g., here and here), but I would like to get a more definitive and mathematically formal answer.
The Earth rotates around its axis, around the Sun, and participates in ...
- 60.4k
2
votes
2
answers
207
views
Yet Another Twin Paradox Question - Is orbit an inertial reference frame?
This question The "Satellite Paradox": Twin paradox in orbiting satellites asks something similar, but none of the answers quite get at the meat of what I'm trying to understand. On the ...
- 215
3
votes
2
answers
247
views
Quantum gravity in an accelerated frame of reference
It is said that we can't study quantum gravity because gravity is a weak force. But gravity and acceleration are the same. Why can't we study quantum gravity in a strongly accelerated frame of ...
- 31
1
vote
0
answers
87
views
Can the spin connection defind on an orthonormal frame be non-metric compatible?
In the (holonomic) coordinate frame {$\partial_\mu$} with the affine connection $\Gamma^\alpha_{~\beta \gamma}$ and a generic metric $g_{\mu \nu}$, the manifold can acquire both torsion $T_{\alpha \...
1
vote
1
answer
198
views
Can an observer in a double tidal locked system figure out it is orbiting?
Tidal locking, when the spin rate of a body matches the orbital rate so that it always faces the other body with the same side, usually occurs for just one of the bodies in orbit. However, there are ...
- 310
8
votes
2
answers
569
views
Mach's principle and a reference frame for acceleration
Although there are different statements of Mach's principle, one statement could be that acceleration is meaningless unless it can be defined relative to something. The distance stars provide a fixed ...
- 13.7k
0
votes
2
answers
757
views
Is it possible to generate artificial gravity without using a centrifuge system?
I was doing research on General Relativity and Einstein's field equations and pondered on a device using that would generate artificial gravity without the use of rotational forces. I wondered since ...
1
vote
3
answers
115
views
Newtonian physics and equivalence principle: a doubt on acceleration and gravity
First of all, the famous Einstein's elevator experiment is quite clear in my head, both of versions.
But now, consider the following:
Suppose then you wake up inside a car that is traveling in ...
20
votes
14
answers
6k
views
Why don't you feel gravity the same way you feel a car's acceleration? [closed]
If you are in an accelerating car or spaceship you feel an apparent force pushing you backwards, which as I understand is due to your own body's inertia (it wants to keep its current velocity but the ...
- 317
3
votes
1
answer
191
views
Is inertia still considered a mysterious force?
When I first saw, for example, weightless objects in a space capsule, I assumed that pushing them would require no effort because, of course, they did not weigh anything. On Earth, heavy objects are ...
- 2,238
1
vote
1
answer
69
views
Conditions for Schwarzschild Metric to be applicable
The Wikipedia article regarding the two-body problem in General Relativity states that the Schwarzschild metric "corresponds to the external gravitational field of a stationary, uncharged, non-...
- 2,712
0
votes
1
answer
108
views
Are there different types of gravitational forces based on different types of masses ( inertial or relative etc)
There are different types of masses like inertial mass, passive gravitational mass, active gravitational mass, relative mass, et cetera. does Are there different types of gravitational forces that is ...
- 33
0
votes
2
answers
113
views
Nature of gravitation field
In many books, a truth of gravitation field has been stated in the following way: "No matter what mass does matter have, all objects will follow exactly the same trajectory under the action done ...
- 377
1
vote
1
answer
295
views
How can we explain the infinite time period of a simple pendulum in an artificial satellite from ground's frame of reference?
If we sit in the satellite's frame of reference(which is non-inertial because the satellite is accelerating) the pendulum's bob will feel a pseudo force just opposite to the gravitational force being ...
- 23
2
votes
2
answers
192
views
Effect of velocity on gravitational force
If I am aboard a spacecraft and have with me two identical metal spheres having rest mass $= m$, what happens to the gravitational force between these two spheres as the space craft velocity ...
0
votes
1
answer
104
views
A problem regarding light bending
My professor in his lectures has stated that a consequence of Einstein Equivalence Principle (EEP) alone is that light bends in a gravitational field.
The proof went as follow: Imagine to be a free ...
- 4,577
0
votes
1
answer
93
views
Non-existence of Lorentz frame at rest on Earth
So, I was reading Schutz First Course in General Relativity and in chapter 5 is states that " If SR is to be valid in a gravitational field, it is natural guess to assume that laboratory frame at ...
- 53
13
votes
6
answers
2k
views
Is spacetime curved in a near-earth-free-falling-object's frame of reference?
If I float motionless in outer space, I will measure spacetime to be approximately flat.
By the equivalence principle, I will get flat spacetime if I am free falling near earth.
Is this right? ...
- 131
1
vote
1
answer
110
views
Strong gravitational field equivalent to accelerated frame
I have recently learned about the equivalence principle and what it says is that( If I have understood it properly) the trajectory of the particles will be the same irrespective of the properties of ...
- 135
1
vote
0
answers
92
views
What is centrifugal force relative to? [duplicate]
Edit- the answer is mach's principle and mach's principle is sketchy so there is no good answer.
So I understand that centrifugal force is really just inertia and stuff but I still have a question.
...
- 11
0
votes
1
answer
194
views
Brans-Dicke gravity and the fifth force
In Brans-Dicke gravity, we have the following gravitational action:
$S_{BD} = \frac{1}{16\pi}\int d^4 x \sqrt{-g} [\phi R - \frac{\omega}{\phi}(\nabla \phi)^2] + S_m[g_{\mu \nu}; \Psi_n]$,
with $S_m$...
- 558
1
vote
1
answer
78
views
Can one identify the presence of a gravitational field?
This is a slight modification to the Einstein's relativity thought experiment that I have not been able to find a discussion on.
Suppose that you are in a spaceship with no windows. Is there any ...
- 11
1
vote
2
answers
100
views
Does a gravitational field get transformed when switching from one inertial frame to another?
We know that electric and magnetic fields get transformed when switching from one inertial frame to another as per the rules governed by special relativity. What about gravitational fields?
- 908
-4
votes
1
answer
773
views
If gravity is a fictitious force, could there be a real force counterpart for it atleast locally? [closed]
I wanted to ask the same question in different ways.
1.Consider the below example whereby we have a man M in a box B in outer space. B is acted upon by a force, F. B moves in direction of F. As the ...
- 73
-2
votes
2
answers
150
views
Can artificial force curve spacetime?
By artificial force, I mean a physical force applied by us onto an object which sets it in an accelerated motion (& not a natural force like gravity). eg: hitting a ball. Excuse me if the ...
- 73