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.

learn more… | top users | synonyms

1
vote
0answers
16 views

Gravitational effect at different depths in the earth [duplicate]

Hypothetically, if we could dig to the middle of the earth, how would gravity affect the people and equipment at different depths in the planet? It seems that at the centre, there would be equal ...
0
votes
1answer
48 views

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 ...
1
vote
0answers
48 views

Gravity effect of a star behind the sun during a solar eclipse [closed]

We know that stars blocked by the sun during a solar eclipse may still be observable as if they are not behind the sun but rather visible to the side unblocked by the sun (because the photons are ...
2
votes
0answers
23 views

Gravitational force: Is the gravitational force dependent on the nature of the medium present in between the two masses? [duplicate]

Is the gravitational force dependent on the nature of the medium present in between the two masses?
-6
votes
1answer
116 views

Traveling through time, reaching the past - POSSIBLE? [closed]

I was obsessed in studying the "faith" and I've made several great discoveries. I don't want to publish anything yet, but I have a semi-proven (proven partially) / theories / so I am curious on bones. ...
1
vote
0answers
41 views

Neck size of wormholes in shape dynamics

As far as a dilettante like me knows, in shape dynamics, black holes are really wormholes. What it the expected diameter of the necks of such wormholes (both for regular holes resulting from the ...
0
votes
2answers
54 views

Acceleration due to gravitational force [duplicate]

I need some help with below. So according to Newton's 2nd law, $a=F/m$, for a given mass, the acceleration depends on mass. But acceleration due to gravity is independent of mass. There seems some ...
0
votes
1answer
86 views

Relative speed of Geostationary satellite with respect to earth?

I was wondering whether relative speed of geostationary satellite with respect to earth is zero or not.Since angular velocity of satellite about earth is same as angular speed of earth about its own ...
2
votes
0answers
90 views

Gravitational mass defect

In nuclear physics we have a mass defect by the binding energy of the nuclides. A similar effect appears in the theory of gravitation induced by the gravitational binding energy, which reduces the ...
2
votes
1answer
67 views

Is there a gravitational radiation reaction force?

As you may know, the linearized relativity theory (or gravitoelectromagnetism), obeys equations analogous to Maxwell's equations in electrodynamics. These equations in ED result in the troubling ...
3
votes
2answers
253 views

Is the popular explanation given for gravity in General Relativity misleading? [duplicate]

In most popular explanations of General Relativity, both in print and film/television, gravity is demonstrated using an example of a 2 dimensional plane being flat, then when putting a heavy object in ...
5
votes
1answer
196 views

The cosmological constant as a Lagrange multiplier?

The cosmological constant $\Lambda$ can be introduced into the gravitational action like this : \begin{equation} S = \frac{1}{2 \kappa} \int_{\Omega} (R - 2 \Lambda) \sqrt{-g} \; d^4 x + \text{matter ...
1
vote
0answers
61 views

Is spacetime elastic or inelastic [closed]

If spacetime is nonelastic and the zero mass curvature is zero than local perturbations of spacetime by mass describable as circumference -2r(pi)is less than zero must be balanced by areas of ...
1
vote
0answers
43 views

Non-zero gravitational anomaly

Analogous to the Adler-Jackiw-Bell anomaly of QCD, we have an anomaly in gravity when we consider gravity to be coupled to chiral fermions: \begin{equation} \partial_\nu J^\nu_5\propto R\tilde{R}, ...
1
vote
0answers
30 views

Why escape velocity doesnot depend on angle of projection [duplicate]

For a projectile projected at a certain angle from horizontal, at the highest point its speed is not equal to zero that means only a part of its initial kinetic energy is utilized to raise the ...
0
votes
1answer
47 views

Galileo 5 and 6 satellites testing gravitational time dilation

In today's Guardian there an article titled "Satellite launch accident provides unexpected test of Einstein’s theory" - ...
0
votes
1answer
51 views

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 ...
1
vote
1answer
64 views

Looking for a specific theory concerning Dark Matter [closed]

I am looking for the name of a theory positing that "empty" space itself is not empty, but has substance, and that "fabric" or "substance" is actually what we call Dark Matter. In theory, dark matter ...
0
votes
1answer
59 views

Is there any way to create a globe with gravitational or similar attractive force - earth simulator?

This may sound like a dumb question. Is there anyway to create a miniature version of earth or its gravitational force. A globe or sphere which have force inside it which can attract the things ...
1
vote
0answers
97 views

Black hole's effect on itself with faster than the speed of light [closed]

If something were pulled into a black hole, my understanding is that you would approach the speed of light. Upon hitting the event horizon, you would be moving the speed of light. After that, you ...
2
votes
0answers
47 views

How sensitively can we detect a moon-sized mass of dark matter?

Suppose there is an object with the mass of the moon made entirely of dark matter. Suppose that somehow, it has the same mass density as the moon. By dark matter I mean matter that does not interact ...
1
vote
0answers
123 views

Le Sage's Theory of Gravitation, is “drag” the only reason why this theory fails? [closed]

Le Sage's Theory of Gravitation was originally proposed allready 1690 by Nicolas Fatio, and has ever since been studied by remarkable scientists; Leonhard Eluer once remarked that it was "infinitely ...
1
vote
1answer
92 views

Measure ball's acceleration down inclined plane

If I am asked to devise an experiment to find an expression for the acceleration of a uniform sphere (ball bearing) rolling down an inclined plane, as a function of the angle of incline. Hence deduce ...
0
votes
0answers
31 views

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 ...
1
vote
0answers
83 views

What pressure will stored water at height provide from a pipe? [closed]

A big open tank is filled with water ($10000$ litres) and kept at a height $15$ metres from ground. At its bottom, a pipe of $1.5$ inch diameter and $10$ meter length is connected. The water is ...
6
votes
4answers
394 views

What is the general relativity explanation for why objects at the center of the Earth are weightless?

The idea that as you move through the earth you get a symmetric cancelling of gravitational acceleration which approaches zero acceleration due to gravity at the center of the earth makes a lot of ...
1
vote
0answers
41 views

Boundary condition for holographic Green's function

I understand that to obtain retarded Green's function using AdS/CFT one needs to put ingoing wave boundary condition at the horizon, when one is considering a finite temperature system. For system ...
1
vote
0answers
60 views

Which property do the word Pressure refer to in General Theory of Relativity?

In this course by MIT Alan Guth while delivering the lecture stated " Both Pressure and Energy densities can produce gravitational fields. Negative pressure creates repulsive gravity and positive ...
-6
votes
1answer
70 views

gravity, it's positive or negative? [closed]

what is the direction of gravity, it's positive or negative?
2
votes
0answers
94 views

Can a Set of “Maxwell's Equations” for Newtonian Gravitation be Derived from Newton's Force + Special Relativity?

When I learned about electromagnetism in my first year of undergraduate school, Maxwell's equations were derived roughly in the following way (see also here or in [1]): Gauss's law for a static ...
0
votes
0answers
55 views

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 ...
3
votes
1answer
99 views

Thought experiment on space curvature due to gravity

Let's say you built a huge, straight rigid beam out in space, far from the sun (outside the orbit of Pluto). It is very long, say 200,000 miles long, but can be very narrow. Then you move it to the ...
0
votes
3answers
101 views

Why is the universe expanding while its components actually attract each other?

First of all, what's the difference between gravity & gravitation? Anyway that's not the actual question. If every matter attracts each other toward itself, then wasn't the universe supposed to be ...
1
vote
0answers
18 views

do gravity shows its effect in atomic level? [duplicate]

how much of a effect do gravity shown in atomic level. how significant or negligible is it. i am guessing the effect is small because the mass of nucleus and electron is small. But the distance ...
1
vote
2answers
59 views

What depth should water be filled to in a cylinder flask to make it the most stable

As said in title, a cylinder flask with a mass of 100g and radius of 3 has a center of balence 10cm above the base. Assuming negligible wall thickness, to what depth should water be added to this ...
1
vote
1answer
68 views

What constitutes a force? [duplicate]

There are a few questions on here about why Gravity is not a force, but I'm having trouble grasping why exactly. It sounds to me that Gravity is not a force because it is simply a by-product of mass ...
1
vote
0answers
69 views

Why gravitational collapse always end up in a black-hole singularity? [closed]

I know the positive energy condition and the singularity theorems by Penrose and Hawking. But still, why people didn't work on gravitational collapse to some exotic matter with an event horizon?// My ...
81
votes
10answers
13k views

If gravity isn't a force, then why do we learn in school that it is?

I have studied some of Einstein's Theory of General Relativity, and I understand that it states that gravity isn't a force but rather the effects of objects curving space-time. If this is true, then ...
0
votes
0answers
82 views

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 ...
4
votes
3answers
290 views

Is there proof gravity bends space or is it just the most convenient explanation?

I have read this sentence in an article: The theory [of general relativity] holds that gravity is geometry: particles are deflected when they pass near a massive object not because they feel a ...
1
vote
1answer
62 views

Comet's distance with and without gravity [closed]

I've got this question that I just can't seem to answer. The question is as follows: A comet approaches the solar system with velocity v and would, if the sun would not attract the comet, pass the ...
0
votes
1answer
28 views

Have hypothetical particles with gravitational mass unequal to their inertial mass been proposed in the past, e.g. as candidates for dark matter?

This is a question about history. To my understanding the equivalence of intertial and gravitational mass for all known particles is a weird empirical coincidence that has been confirmed to high ...
2
votes
2answers
84 views

Would a person in a gravity well observe the sky as rapidly moving due to time shift?

Inspired by the movie Interstellar (2014) - I was wondering about the crew on the surface of the planet which was deep in the gravity field of the black hole (Gargantua) - if they would look up at the ...
1
vote
0answers
36 views

Thermal AdS3 in Chern Simons

I am currently working with (2+1) gravity in Chern-Simons formulation and I have a question about thermal AdS. The way I understand that one retrieves thermal AdS is by Wick rotation and ...
-3
votes
1answer
211 views

Gravitational constant, $G$, What if it is not Constant?

The question is on title; What if Gravitational Constant, $G$, is not constant? Let's skip all the local consequences if it would suddenly change, like asked here; Can gravitational constant be ...
-1
votes
1answer
40 views

How can the speed and the mechanics of light be similar to the speed and the mechanics of gravity? [duplicate]

How can the speed and the mechanics of light be similar to the speed and the mechanics of gravity? Most say that light cannot escape a black hole. Then gravity cannot escape a black hole either, so ...
1
vote
2answers
115 views

Changing orbit of a space shuttle

In the figure here, a space shuttle is initially in a circular orbit of radius r about Earth. At point P, the pilot briefly fires a forward-pointing thruster to decrease the shuttle’s kinetic energy K ...
5
votes
2answers
377 views

Gravitational waves and time

Two questions. It is said that time can only go slower in gravity fields and if you move faster. I have heard that when a gravitational wave pass earth then the space/time vibrate and time change ...
0
votes
1answer
23 views

Equation for Turning Projectile

I'm trying to cook up an equation that will give me position for a projectile which operates in the Newtonian Domain. So a the fall equation is: $$\mathbf{p_t} = \frac{\mathbf gt^2}{2} + ...
0
votes
1answer
41 views

How can one interaction influence the way another interaction generates mass?

This question arose as a follow-up of this one and applies generally to all interactions and all ways to generate mass. To make it clear, I take here the example of the neutron, whose mass is in ...