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1answer
77 views

Showing $m_I = m_g$ follows from the equivalence principle

The inertial mass of an object is defined as its resistance to acceleration by $\vec{F}_{net} = m_I\vec{a}$. The gravitational mass of an object is defined as the scaling of the gravitational force an ...
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2answers
69 views

What exactly is the relationship between gravity and acceleration?

I know that one of Einstein's key steps towards General Relativity was the realization that gravity and acceleration were related. I understand the free-falling elevator analogy, but the relationship ...
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1answer
252 views

Geometric formulation of the equivalence principle

Let $(M,g)$ be a $4$-dimensional Lorentzian manifold. It is well know that given $(U,\psi=(x^1,\ldots,x^4))$ local chart around some $p\in M$, it is posible to find a change of coordinates given by $(...
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3answers
69 views

Second Law of Dynamics and Pulleys

The system in the figure is initially at rest . If the system starts to move , evaluate the acceleration of the block $A$. Mass of the block $A$ is $m_A = 60\;\mathrm{kg}$ ; mass of blocks $B$ and $C$ ...
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3answers
135 views

What is “a general covariant formulation of newtonian mechanics”?

I am a little confused: I read that there are general covariant formulations of Newtonian mechanics (e.g. here). I always thought: 1) A theory is covariant with respect to a group of transformations ...
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2answers
55 views

Locally remove a gravitational field

Let $K$ be an inertial frame of reference on $\mathbb{R}^3$ and $g=g(t,x)$ a nonuniform and nonstatic gravitational field. How I can choose a system of reference $\bar K$ such that mechanical effects ...
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1answer
54 views

Does curved spacetime arise from inhomogeneity of gravitational field?

In general relativity textbooks such as Sean Carroll's Spacetime and Geometry, there is often a line of reasoning that goes like this: Strong equivalence principle states that free falling frames ...
2
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1answer
48 views

An example of a theory that respects the Weak Equivalence Principle but violates the Einstein Equivalence Principle

The Weak Equivalence Principle has any one of the following forms: the inertial mass is equal to the gravitational mass there exists a preferred class of trajectories through spacetime, known as ...
3
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1answer
53 views

Difference between Fermi and Riemann normal coordinates

What is the difference between Fermi normal coordinates and Riemann normal coordinates? Which one of them is related to the vanishing of the Christoffel symbols?
3
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1answer
59 views

Does the Equivalence Principal account for inverse square law?

I realize this must have been considered but please explain what I am missing. My understanding is that the Equivalence Principal states essentially that someone in a closed cabin accelerating at 9.8 ...
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1answer
87 views

How does acceleration feel compared to gravitational pull?

I was debating a variation of this Phys.SE question with a friend. The original question is: "If you had your eyes closed, could you distinguish between standing still on earth and being in a ...
0
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1answer
48 views

Can a body under weightlessness detect if it's under free fall or under a zero gravity field?

My first thought was to use an accelerometer. However, quoting from wikipedia, an accelerometer at rest on the surface of the Earth will measure an acceleration g= 9.81 m/s2 straight upwards. By ...
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1answer
27 views

Distinguishing inertial reference frames

As described in Wikipedia as well as this entry here, "being at rest on the surface of the Earth is equivalent to being inside a spaceship (far from any sources of gravity) that is being accelerated ...
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0answers
16 views

How does curved space make an obejct move toward Earth? [duplicate]

I think I understand how the equivalence principle shows how light can bend and therefore space must be curved. What I do not understand is how curved space makes an object move directly toward the ...
1
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1answer
48 views

Einstein's Principle of Equivalence - Infinite Acceleration/Energy?

Hello and thank you for your time. I've been wondering about Einstein's Equivalence Principle core idea. That is, from experiment alone, one cannot differentiate between a gravitational field and a ...
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2answers
32 views

Practical limit of equivalence principle

The equivalence principle says, for a small elevator, it is not possible to distinguish between a closed elevator moving at a constant acceleration, and the same amount of gravitational acceleration ...
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2answers
159 views

Concept of mass

In classical mechanics, there seems to be a need to distinguish between inertial and gravitational mass. Some texts show how the concept of mass may be defined with some mathematical rigor. There is ...
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3answers
330 views

Can an observer know what is the source of gravity?

There's an observer in a closed room without windows under an influence of gravity force. Can he determine what is the source of gravity - whether it's a spinning motion, acceleration or huge mass ...
0
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1answer
98 views

The equivalence principle and identifying free-fall as a locally inertial frame

As far as I understand it the equivalence principle in general relativity is the statement that a frame at rest in a uniform gravitational field is equivalent (indistinguishable) to an accelerated (...
0
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1answer
183 views

LIGO discovery: if the space “time” metric is changed, how is it measured? [duplicate]

Regarding the wonderful 2016 news about gravitational waves. Travel time in one arm of the LIGO is ~ 30μs. A gravitational wave affects the arm for some few hundred of these laps. Then for example ...
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1answer
47 views

Gravity, Acceleration, Time Dilation and the Equivalence Principle

Three clocks are started at exactly the same time on Earth. The first and second clocks are taken into the vacuum of space. The first clock accelerates until it reaches 100,000m/s, then stays at this ...
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1answer
70 views

Graviton detector thought experiment

I was recently thinking of a thought experiment: Assumptions Graviton detectors can exist The equivalence principle will hold in the final theory of quantum gravity We can accelerate the graviton ...
3
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0answers
60 views

What is the inertial mass of a black hole?

Or the inertial mass of any spherically symmetric object, can I calculated by measuring very accurately the spacetime distortion this object produces in its surroundings? With 'inertial mass' I mean ...
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4answers
256 views

Can there be acceleration without velocity?

If I was in a spaceship continually accelerating at $9.81m/s^2 =1g$ in a straight line, I would reach near light speed within a year. On Earth, we are in a gravitational field of $1g$, which ...
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2answers
52 views

Time dilation and freefall (follow up and simplification) [closed]

A person is four miles up in the atmosphere, and freefalls towards earth. Another person is standing on earth, watching them come down. During this period of freefall, which person experiences more ...
0
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1answer
51 views

Acceleration in Space

Lets assume a body with a certain mass is in a region of space that has zero $g$ (or pretty close to zero $g$). Would acceleration in a straight line produce $g$-forces? Would that mass acquire ...
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0answers
38 views

Dark Matter and Equivalence Principle

Dark Matter effects show up in galaxies. Why isn't it considered as a violation of equivalence principle instead of assuming all these extra non-interacting particles as gravitational mass and ...
0
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1answer
156 views

F=ma is true in an accelerating coordinate system [closed]

There are plenty of similar topics about the physical or intuitive meaning of the equivalence principle or statement such as ''laws of physics are true in every frame of reference''. Usually answers ...
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0answers
69 views

Is the equivalence principle Machian?

There is a lot of discussion on the subject of Mach's principle, and whether it has any place in the theory of relativity. But it seems to me that one could argue that Mach's principle is at the heart ...
0
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1answer
43 views

Is a force acting on a freely falling body? [duplicate]

Albert Einstein in his equivalence principle stated that a freely falling body does not experience force, but if I let a ball free fall its velocity increases periodically (it accelerates). How is ...
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0answers
69 views

Bending of light in a gravitational field & the principle of equivalence

I have a few conceptual issues following a standard thought experiment to argue why light bends in a gravitational field and I'm hoping I can clear them up here. Consider an observer in a lift in ...
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0answers
24 views

Does any ordinary object emit radiation due to Unruh effect and equivalence principle? [duplicate]

I am just wondering is there Hawking radiation for any object (that has mass) due to its gravity. Base on the Unruh effect and equivalence principle, any object should emit Black-body radiation or ...
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2answers
88 views

How does general relativity explain the impact force after radial inward fall toward Earth?

I understand that, in the context of the Schwarzschild spacetime (General Relativity), a radially inward falling observer follows a time-like geodesic with zero four-acceleration. There are no forces ...
1
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1answer
75 views

Einstein equivalence principle cannot entirely predict gravitational time dilation

The Einstein equivalence principle can be used to derive the gravitational redshift of photons, but it does so in an unusual way. The derivation is as follows. Consider an source of photons on the ...
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0answers
31 views

Energy-Mass Equivalence applied to governing equations

To start off with this is an extremely general (vague) questions, and as such I expect vague answers. I've recently been studying the Navier-Stokes equations which govern fluid motion. These ...
0
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1answer
105 views

Accelerated reference frame in Minkowski space vs pure gravitational field

I just finished reading Einstein's "Relativity: The special and the General Theory", and if I understand Einstein correctly, he says that an accelerated reference frame in Minkowski space (i.e., empty ...
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1answer
31 views

EM wave generation from different frames of reference

Take 2 observers and a charged particle, Observer S is stationary to the particle and sees the electric field and no magnetic field as he is stationary to the particle. Observer A decides to ...
6
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1answer
205 views

Why must inertial mass and gravitational mass be equal, not just proportional?

I'm certain I'm just under a grave misapprehension. I really just don't understand how one can conclude that inertial mass is equal to gravitational mass. It seems to me that we've simply scaled our "...
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2answers
125 views

Falling with same acceleration and meaning of gravity

My question is what does falling with same acceleration has to do with what Einstein concluded concerning the gravity in terms of the curvature?
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0answers
41 views

Is there any such thing as gravity? [duplicate]

So I was seeing this documentary and ended up knowing that there is no such thing as gravity. It said that we are not being pulled by Earth but being pushed by the space time curvature acc. to general ...
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2answers
66 views

Principle of equivalence

Einstein's principle of equivalence states that one can not distinguish between a freely falling nonrotating system in a gravitational field and a uniformly moving system in the absence of a ...
1
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2answers
83 views

Black Hole horizons and the Equivalence Principle?

In the reference frame of a freefalling observer, does crossing the event horizon not cause a contradiction between two classical principles that supposedly apply at the event horizon: the equivalence ...
3
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1answer
49 views

What does gravitational mass mean if (weak) equivalence principle invalid? [closed]

As equivalence principle states Mass and weight are locally in identical ratio for all bodies. --Newton This implies that the gravitational mass does only depends on its inertial mass. Suppose ...
0
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1answer
31 views

The equivalence principle and experiments concerning it?

Imagine that we are in a rocket accelerating with some magnitude $a_1 = dx^2/d^2t$, also imagine that we have a stationary rocket ship in close proximity to ours, stationary relative to our reference ...
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3answers
117 views

Einstein's principle of equivalence; Standing on earth vs sitting in accelerated car

When I am seated in a car that is accelerating in a particular direction I could, for example, throw a ball and it would appear to be flying the opposite way. With the windows covered etc. An ...
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8answers
13k views

Why does a free-falling body experience no force despite accelerating?

Note: For the purposes of my question, when I refer to free fall assume it takes place in a vacuum. From my (admittedly weak) understanding of the equivalence principle, falling in a gravitational ...
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1answer
154 views

Curvature of spacetime and the equivalence principle

Assuming the Einstein equivalence principle, formulated as following: The outcome of any local non-gravitational experiment in a freely falling laboratory is independent of the velocity of the ...
1
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1answer
627 views

Graviton and principle of equivalence

Is it possible that in a theory of gravitons, i.e., a quantum field theory of gravitation, general relativity's principle of the equivalence of gravitational mass and inertial mass, no longer holds?
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6answers
5k views

Does a person inside a falling bus fall to the front of it?

So I was watching Final Destination 5 and something caught my attention. There's a part where a bridge collapses and everything falls apart, so there's this bus that has a person inside (unaware of ...
3
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3answers
264 views

I think I am misunderstanding Einstein's equivalence principle and his elevator

I'm having difficulties understanding why a gravitational acceleration can be guaranteed to be locally equivalent to an accelerating frame. Doesn't it matter on how the force is being applied? If the ...