# Tagged Questions

Gravity is an attractive force that affects and is effected by all mass and - in general relativity - energy, pressure and stress. Prefer newtonian-gravity or general-relativity if sensible.

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### Calculating the force of someone falling backwards

Say someone was standing and fell backwards. Knowing their mass and height, would it be possible to calculating the force they hit the ground with, not accounting for air resistance? What I've tried: ...
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### Can we use gravity for faster than light communication? [duplicate]

I have been told that I am being affected by the gravity of everything in the universe - that even the most distant matter is exerting a gravitational force on me. If this is true, I have wondered how ...
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### Spherically Symmetric Metric in Nordstrom gravity

Nordstrom's theory of gravity postulates that the metric is of the form $g_{\mu \nu} = \phi ^2 (x) \eta_{\mu \nu}.$ The field equations, in vacuum are of the form $R=0$, where $R$ is the Ricci ...
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### Gravity: Why Do things fall to Earth? [duplicate]

If gravity is in reality spacetime geometry why when I drop an object on the surface of the Earth does it fall to the ground? Does spacetime push it?
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### Sitting to Standing Posture Transition Accelerometer Triaxial Data Explanation

I don't have a physics background. (I'm a Computer Science student) I have a waist-worn accelerometer provided by the school which is quite reliable. I've captured data of sitting still to standing ...
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### What unusual effects will we observe on the non-rotating Dyson sphere with earth gravity around the Sun?

First let's place our sphere Let's assume there is a two-layer non-rotating Dyson sphere around the Sun (ignore the scale): Green is empty air. How far should the inner border of this sphere be ...
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### How person in different gravity field be seen?

We know that gravity affects time. More the gravity, slower the time, and vice-versa. Now consider a hypothetical condition where two people are walking next to each other. One person is subjected ...
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### Deriving Kepler's First Law from Newton's Law of Universal Gravitation: Interpretation of the $u = 1/r$ change of variable

I'm working through a somewhat unsatisfying derivation of Kepler's First Law from Newton's Law of Universal Gravitation. The key to obtaining the equation of motion that you can solve lies in making ...
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### Gravity's force on space

Here is a quote from Brian Greene, The Fabric of the Cosmos: Space, Time, and the Texture of Reality, p. 273: “The early universe provided an arena in which gravity exerted its repulsive side with ...
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### Are all forces explained in terms of curved spacetime? [duplicate]

Gravity is explained in general relativity as curved spacetime. Can the other forces (electromagnetic and weak/strong nuclear) also be explained by this?
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### Can the curvature of space be measured using a swimming pool?

I read somewhere that if the center of mass of two twelve ton elephants was one meter apart then the space they curve would be one nanometer longer. (Though I doubt elephants come that dense) This ...
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### How do I find the energy difference between two points of a gravitational gradient?

What I'm ultimately trying to figure out is how to calculate only the potential energy attributed to the differences in the force of gravity at two distances from the Earth's center of gravity.
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### Would a fast moving (approaching $c$) stream of particles be affected by the gravitational pull of a gas giant?

I was inspired by this SE question. Would the gravitational field of a gas giant (such as Yavin IV) have an effect on the super laser (i.e. slow it down, change the direction), or is the mass so ...
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### Gravity and centre of mass

Does gravity act entirely as if on the centre of mass? Often I have heard this, but it seems more realistic (even if less practical) if it acts on individual bits of matter, therefore weaker further ...
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### Expanding Electric Field, Magnetic Field in post-Newtonian Gravitational Potential

I've cross-posted this question from Mathematics since Physics is probably better suited for the nature of the question. I've ...
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### Gravitational intensity [closed]

I calculated the gravitational intensity and potential at a point P due to a horizontal linear mass distribution of length '$L$', mass '$M$' and uniform linear density at a distance '$R$' apart from ...
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### Books on Spin-2 Gravity / Fierz-Pauli theory

I am trying to find a good pedagogical book/set of notes on Gravity as a spin-2 particle. I have been reading through Gravity & Strings by Ortin but it's very brief and offers little justification/...
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### Singular isothermal density distribution

Does anyone know where the Singular isothermal density distribution $$\rho(r)=\frac{\sigma_{V}^{2}}{2\pi\,G\,r^{2}}$$ or how it was derived. Are there any good references on how this equation was ...
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### 2D space-time curvature [closed]

Actually, why is the space-time curvature considered 2D plane. As 2-D dimensional space-time curve is used to explain why moon revolves around the earth stating because the massive objects wraps the ...
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### If a spaceship accelerates enough can it overcome spaghettification?

If a spaceship accelerates at the right amount would that counteract the spaghettification caused by falling into a black hole?
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### How does space-time behaves between opposite gravitational pulls? [duplicate]

this is my first question in physics.stackexchange. I'll try to be more specific. I have a very basic understanding that time flows (is there a better word?) differently depending on the gravity ...
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### Problems of General Relativity on small and large scales [duplicate]

As far as I know, the most important problem of GR on large scales is the cosmological constant problem which in some manner can be thought of as a dark energy problem (please correct me if I am wrong)...
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### Can you use the force of gravity (ie. surface of Earth = 9.8m/s^2) to calculate gravitational time dilation?

I am having trouble tying the Schwarzschild radius to gravitational force as I believe it is not fixed when considering different masses. I am getting results that show a different time dilation for ...
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### Gravitational boson violating relativity [duplicate]

Currently doing a introductory degree level physics course, they were talking about how changes in gravity/gravitational field cause changes so quickly that if you assigned it the "graviton" said ...
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### Is it possible to directly test whether of not the vacuum gravitates?

According to GR, all sources of stress-energy (e.g. everything on the $T_{\mu\nu}$ side of the EFE) should gravitate (e.g. affect the curvature/$G_{\mu\nu}$ side of the EFE). We observe the expansion ...
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### Vibrating water container problem

I am struggling with visualising and understanding the phrasing of this question - cross posted from Math stack exchange since this forum is more appropriate: "A water-filled container is ...
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### What force causes massive objects to bend space? [duplicate]

The visualization of gravity as shown by this video is pretty good at explaining how massive objects bend space, and such bending causes objects around it to fall towards it (a.k.a: gravity). However,...
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### Scalar gravity coupled to matter

I am reading Ortin's Gravity and Strings and trying to understand the generalisation of Newtonian Gravity to a relativistic field theory. On page 47 (link above) he motivates the study of the Poisson ...