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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Gravitational waves vs. electromagnetic for telecommunications

Assuming it would be possible, what would be the advantages/disadvantages of manipulating gravitational waves for telecommunications versus using electromagnetic?
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Explanation of galaxy rotation curves by space-time drag

I expect, that known effect of rotating body (made of galaxy stellar mass) it too small to explain galaxy rotation curves. By how small is it comparing to required value? What if introduce ...
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The Validity of a Heuristic Explanation of Black Hole Complementarity?

In one of the messenger lectures at Cornell in 2013, Leonard Susskind gave a heuristic argument for black hole complementarity. Suppose Alice is stationed far away from a Schwarzschild black hole and ...
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Why is gravity viewed as a force? [on hold]

Before I say my thoughts on this I wanted to state that most of my knowledge on physics and such is from college books, and not from actual instruction. From my understanding of forces, there must be ...
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slippery slope facts of spherical and plane object [on hold]

Imagine a slippery slope and from the top of the slope I threw two object one is spherical stone and the other is plane box. Why the stone would reach the bottom by rolling randomly where the box ...
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1answer
43 views

Does gravity cause the gravity of another mass to curve?

For example say star 1 is at position x, however star 2 causes gravitational lensing on star 1's light that is traveling toward you and you now see star 1 at position y. Will star 1's gravity move you ...
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Can we make high acceleration safe to our bodies thanks to this gravity trick?

According to Wikipedia, a human body can resist g-force of about $5 g$. It can be a greater value in some circumstances, but even as low as $2 g$ would be unpleasant after several seconds. This means ...
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23 views

Gravity of Masses in 4-D [closed]

I have developed a fairly stable understanding of the curvature of spacetime caused by a massive object (meaning with mass, not necessarily a lot of mass), though I have been wondering about a new ...
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3answers
114 views

How did the constant $\pi$ creep into Einstein's field equation? [duplicate]

The ratio of a circle to its diameter in Euclidean space appears in places that sometimes appear to be mysterious. I am wondering if in Einstein's field equations he is using Poisson's formulation of ...
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How does critical density affect the expansion of the universe if gravity is the curvature of space-time?

From what I know there are three scenarios about the end and expansion of the universe that all depend on the concept of critical density: If the matter of our universe is above critical density, ...
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50 views

Would order 1AU metric expansion of space begin if the solar system were not inside a galaxy?

In this question I describe the >30 years of laser ranging between lasers on Earth and the retroreflector arrays on the Moon. Amazingly, after comparing this data to simulation of all of the orbital ...
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160 views

Will the Graviton discovery mean the end of the General Relativity [closed]

I know that this question has been addressed in one form or the other however I would appreciate some other thoughts - other then "GR works so it doesn't matter what's behind it". In fact it does ...
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2answers
93 views

How to best cut this fallen tree? [closed]

I have a fallen tree. The root structure is painted dark brown, is nearly perpendicular to the ground and is about 12 feet tall. The main trunk is lighter brown and is supported on the ground by a ...
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1answer
59 views

Calculate the gravitational force between two stars having common centre

Two star of mass $M$ and $2M$, a distance $3x$ apart, rotate in circles about their common centre of mass $O$. Express the gravitational force acting on the stars in terms of $G,M$ and $x$. I ...
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most efficient set of weights with whole number mass to n-power for balancing unknown mass on vertex of regular triangle

I saw this qustion: http://puzzling.stackexchange.com/questions/186/whats-the-fewest-weights-you-need-to-balance-any-weight-from-1-to-40-pounds Suppose you want to create a set of weights so ...
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2answers
71 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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25 views

Can the mass of air bubble in material medium be considered negative?

When I was going through the chapter of "GRAVITATION" from high school level physics book, I encountered a problem with a statement made. I couldn't make out the clear vision regarding the following: "...
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1answer
13 views

Potential and Field for a sphere with a central core of differing density [closed]

A spherically symmetric planet of radius $a$ consists of a central core of radius $b(<a)$ of uniform density $\rho_1$ surrounded by an outer region of uniform density $\rho_2$. Obtain an expression ...
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1answer
42 views

Electron traveling through gravitational and magnetic field

When an electron travels through a magnetic field it experiences the Lorentz force. The force acting on the electron causes an acceleration and therefore Cyclotron radiation is emitted. After reading ...
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124 views

Visualizing gravity

When you see graphics trying to help people visualize what gravity in Einstein's relativity "looks" like it will often be a mostly two-dimensional plane with a concave warp where a massive object is ...
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How to calculate the lensing amplification of the weak field images in schwartzchild metric?

In Strong field limit of black hole gravitational lensing, Bozza et al state (without proof) that the amplification of each weak field image is given by $$ \mu_{wfi}=\frac{1}{\beta}\sqrt{\frac{2\,D_{...
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12 views

How does a position based force work on a torus?

Consider a 2 particle system in $\Bbb R^2$. Let's say they have some force acting between them. For the sake of argument let that be $F=\mathbf r/|\mathbf r|^3$. This is a simple inverse square system ...
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1answer
45 views

g force when freefalling on different planet

My understanding is that g force is apparent weight/normal Earth weight, and is calculated by a+g/g where g=9.8. Now, apparent weight is the total force exerted on an object by its support, which is ...
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1answer
52 views

Is it equally difficult to lift something as it is to lower it?

This just seems a bit counterintuitive cause lifting stuff seems harder, but if I do them at the same, constant speed, I will apply the same force opposing gravity, just over opposite displacements, ...
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3answers
105 views

What is the connection between inertial/gravitational mass and relativity?

In Einstein/Infield 's The Evolution of Physics (32-35) the authors establish that inertial mass and gravitational mass are the same and then connect this to relativity.Throughout these pages I was ...
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44 views

A function for calculating velocity at several distances as you fall towards the earth's center

Assuming there is no drag, no friction and no other objects affecting you. If you drop into the earth (through a tube). Your velocity will be 7900 m/s at the center of the earth according to http://...
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122 views

Does a planet/star itself lose mass when it 'emits' gravitational waves?

Orbiting planets and stars can create gravitational waves, as seen with the LIGO. But are they also losing mass-energy. Beside that, the kinetic energy associated with their orbital angular momentum ...
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4answers
68 views

Gravitational potential energy defined in terms of work

An outcome of my high school syllabus is to "define gravitational potential energy as the work done to move an object from a very large distance away to a point in a gravitational field: $-GMm/r$". ...
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28 views

Resources on how to estimate the power density of gravity?

If a drop a ball from a height $h$, the work done by gravity (in this particular situation $i$) is $w_i=\int_0^h F_G \cdot dl \approx mgh$. What I would like, is to estimate the work done by gravity ...
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2answers
36 views

Is the magnitude and direction of gravity on an object the same as the objects vertical velocity?

I need to make a diagram for an entry level college physics class. I need to show the magnitude and direction of gravity on a flying object and also show the magnitude and direction of the objects ...
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2answers
293 views

Atomic Weight and Time Dilation

So, this might sound kind of ridiculous but I was thinking about Relativity and since Gravity is a warping of Space-Time, or Time Dilation, why don't we measure Atomic Mass in Units of Time Dilation? ...
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112 views

Metric transformation, polygons and gravitons

I'm trying to understand the paper by Hitchin called: ''Polygons and gravitons". I'm stuck at page 471. At this point, he does some computations and obtains a metric: $$ \gamma dz d\bar{z}+\...
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62 views

Position / velocity / acceleration vs time graphs when falling towards a black hole

In Newtonian physics, as far as I understand it, for a small object falling towards a massive object, the graphs of position, speed and acceleration vs time look like this: (If the massive object ...
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What is the difference between $\theta^{0}_{n}$ and $\theta_n$ in Strong gravitational lensing?

I am currently studying the strong gravitational lensing effects by general relativity. However, when studying these effects I came across several paper (especially these two papers, Paper One and ...
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Is critical mass of fissile material the same in gravitational fields with different force?

Let's take plutonium-239 for example. $10\, Kg$ (sphere $9.9\, cm$) need for a nuclear reaction. Are we talking about these numbers in Earth environment with $\approx 9.8\, m/s^2$ gravitational ...
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1answer
63 views

How Long Did It Take For The Sun To Form?

I realise this may be a difficult question to answer because, AFAIK, we don't have an accurate estimate of the size of the protostellar cloud, or whether our sun formed from a subsection of a much ...
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What is signifcance of density of the universe if it changes?

So theories of expansion of the universe (before dark matter and energy) said that the ultimate fate of the universe is based on the density of the universe and this being compared to the critical ...
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1answer
52 views

Are there any numerical predictions of the Newtonian gravitational constant $G$ from modern theories?

There are no established relationships between the Newtonian gravitational constant $G$ and other fundamental constants, so there is no way to derive its value from other quantities. Its value must be ...
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1answer
50 views

Confirmation of a concept under General Relativity and Frames of Reference

I would like to preface this by saying that this isn't necessarily meant to be a full question, though it may become that, but it rather a confirmation of my understanding of a concept. Newton would ...
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34 views

Why is the water still in the glass while rolling?

Pilot drinks glass of water while rolling the plane. The water stays in the glass, even if the plane is upside down. How is this possible? Why doesn't the water leave the glass, as it does when I ...
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1answer
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Black hole gravity at bottom (deepest end) [closed]

If black holes are hole in space and time then at bottom or below bottom there is no more gravity of black hole. As any hole has an end (Deepest end). Is this true ? ******** EDIT *********** http:/...
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1answer
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How to calculate orbit of a sphere around a bigger one in microgravity?

I don't have any knowledge in physics, but in a world building related question, I need to know how can I calculate the orbit or the distance in each point of the orbit around a spherical object in ...
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1answer
1k views

Is running in a zigzag helpful in avoiding being shot by an arrow? [closed]

Two people A and B start at a certain point. B runs away from A to another point. A shoots arrows at B. Is it helpful for A to run in a zigzag rather than in a constant direction? To be more ...
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1answer
17 views

Position of normal to the free surface of a liquid

If the free surface of a liquid resting in an inertial frame is horizontal. Does the normal to the free surface pass through the centre of the earth. I wonder what will be the outcome if the liquid is ...
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4answers
199 views

Does Dark Matter Exert The Same Gravitational Force As Ordinary Matter?

I have read through this Wikipedia article on Dark Matter and it contains references to the methods used to demonstrate the existence of dark matter. A galaxy rotation curve is a plot of the ...
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103 views

Deriving the field equations for a dark energy / modified gravity effective field theory

Question I'm trying to derive the modified gravity EFT field equations and, from their 00 component, this Friedmann equation: \begin{equation} H^{2}+H\frac{\dot{\Omega}}{\Omega}=\frac{\kappa \rho_{m}+...
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2answers
106 views

Can two heavy objects circling around each other be separated because the speed of gravity?

Imagine two massive objects, with the same mass (M) circling around each other at equal distances from the centre of mass (C.M.). Their distance is 1 lightour. Don´t the two bodies get accelerated and ...
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Is the Weitzenböck connection the only connection with Torsion but without Curvature?

In teleparallel gravity, the (local) connection coefficients of the Weitzenböck connection are given by $$ \Pi^{\beta}{}_{\mu\nu}= h^{\beta}_{i} \partial_{\nu}h^{i}_{\mu} - \Gamma^{\beta}{}_{\mu\nu}...
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Is a puffy object heavier than a contracted object?

From here, I know the spring becomes heavier when potential energy stores in it , how about gravitional potential energy? Is the case similar?consider a puffy object, eg, a gas giant, when it ...
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Since there is no absolute reference frame, and if there were only two, how would the two bodies know whether to fall or orbit?

Imagine the earth and a satellite in geostationary orbit. Now subtract the rest of the universe, with nothing else to frame the velocity, and from a certain point of view the two bodies seem to be ...