All Questions
Tagged with gravity reference-frames
103
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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 ...
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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
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2
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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
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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, ...
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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 ...
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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 ?
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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 ...
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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 ...
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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
$$
\partial_t\to D_t=\partial_t-f(t,x)\partial_t\\
\nabla\to ...
- 1,335
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What kind of coordinate change is needed to make gravity disappear?
I understand that the Christoffel symbols associated with the metric will vanish locally once you perform the appropiate change of coordinates. These new coordinates correspond to an observer in free-...
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Are objects in an uniform field inertial?
It is currently understood that gravity is not actually a force, and a fact that is often used to show this is that an object in free fall doesn't "feel" that it is accelerating and is thus ...
- 365
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More on frames of reference and coordinates in GR
I have read other questions concerning this subject, and by now I believe that in order to solve a gravitational problem in GR, one has to basically abandon the notion of frames of reference. However, ...
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If gravity is not a force, then how come gravitational assists work?
I have learned about general relativity and how gravity arises from spacetime curvature. And I have always been taught that gravity is not a real force in the sense that
$$\frac{dp}{dt} = 0$$
And from ...
- 1,896
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119
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Does a linearly accelerated observer inside an inertial spherical charged shell detect an electric field?
The electric field inside a charged spherical shell moving inertially is, per Gauss's law, zero.
If the spherical shell is accelerated, the field inside is not zero anymore, but it gains a non-null ...
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A problem in the light beam experiment of the equivalence principle?
Could someone tell me where i'm wrong? The light beam experiment of the equivalence principle which was the mind experiment that made Einstein deduce the curvature of light around heavy objects, has a ...
user348262
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Weight in Interplanetary Space
How is weight zero in interplanetary
space? The Moon is orbiting the Earth because of the gravitational pull of earth. Then gravity must exist in interplanetary space too. So any body in space must ...
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Is the generating function the phase factor when transforming from inertial to non-inertial coordinates?
Question
When going from the Hamiltonian of an inertial frame $H$ to that of a non-inertial frame $H'$ they are related by the canonical transformation:
$$ H = H' + \frac{\partial F}{\partial t}$$
I ...
- 1,389
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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 ...
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43
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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
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165
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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 ...
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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 ...
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213
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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 ...
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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 ...
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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 ...
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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
...
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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 ...
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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 ...
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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 ...
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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 \...
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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 ...
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