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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Forces that fall under gravitational forces

I was explaining the air motion in the atmosphere, so I introduced Gravity, Pressure Gradient and Coriolis Forces. Then one of the Professors asked me this question, which I couldn't answer. He said ...
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2 balls projected upwards, find the place of collision [on hold]

Problem: A ball is thrown upward with velocity $19.6ms^{-1}.$ A second later, another ball is thrown upward with velocity $9.8ms^{-1}.$ When and where will these 2 stones collide? I recently ...
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29 views

How does energy density affect gravity?

If I have two equal mass of objects, and one is less dense but spread over a larger volume, how does their gravity differ from two masses of equal mass and density? (assuming the given volumes do not ...
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58 views

Is gravity's acceleration rate - squares of all natural numbers?

I've seen some science\history documentary in which they made a replica of Galileo's inclined plane experiment. They rolled a ball down the plane; and it's progressed in length units each unit of ...
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Can the stress energy tensor have nonzero value in a vacuum region?

In general relativity, when solving for the schwartzchild solution, we set $T=0$. 1) Is it possible for the stress energy tensor to have nonzero value in a vacuum region? 2) Is the stress $T=0$ in ...
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Isn't the fact that gravity acts exactly like velocity seem profound? [on hold]

I was just reading something that I guess I knew all along, which is that time slows down as gravity increases. I guess it was the way it was phrased, because I knew that was true with black holes ...
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20 views

Could it ever be possible to generate small gravitational waves?

Would it ever be possible to make a device that could generate small,short gravitational waves? If so, it would then be possible to use artificial gravitation for space travel. Assuming that gravity ...
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4k views

Do you feel gravity?

I have been reading a few articles about the question why we don't feel/notice gravity in everyday life, but I couldn't understand why exactly we don't feel/notice it, that is, why we don't feel a ...
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relations opf space-time to gravitation as an evolutionary process [on hold]

just thoughts - 1 -gravity - could it be that it is not a fundamental force after all - could it be that it evolved after the big bang? space time was evolving and things [lets call them string but ...
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67 views

What is wrong with this theory? - This is a unique way to visualize the universe [on hold]

Assuming that particles move in two ways: 1st, conformationally changing relative to itself over time regardless of its location in 3d space (i.e. staying in one place but conformationally changing) ...
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Is the stress energy tensor continuous at the interface between an object and vacuum?

The stress energy tensor has (as I understand) zero value in the region where there is no matter and non-zero value where there is matter. Suppose there is one matter object in space, now how does the ...
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135 views

Does gravitational field has gravitational mass?

Other questions closely related to the one of the title (as I will show) are Does speak about work done on photon has sense? Does photon has a gravitational mass? Does exists a modern (and more ...
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59 views

Is gravity weak negative electric charge? [duplicate]

This could be true since the both have infinite range and other common properties. They both have fields.
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29 views

In discrete models of spacetime, what are some implications of the Einstein equation

We have several models of discrete spacetime. Sorkin has a causal growth dynamics, there's spin foams, Panangaden showed a correspondence between interval domains and spacetimes. I am looking for ...
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225 views

Is gravitational Chern-Simons action “topological” or not?

Here are the 2+1D gravitational Chern-Simons action of the connection $\Gamma$ or spin-connection: $$ S=\int\Gamma\wedge\mathrm{d}\Gamma + \frac{2}{3}\Gamma\wedge\Gamma\wedge\Gamma \tag{a} $$ $$ ...
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111 views

Can anyone explain me how time can bend according to Einstein in simple way? [duplicate]

I am just 16 and curious to learn about Theory of Relativity. Can any one explain it simple enough for me to understand? I read that it is bending of time-space or space-time that causes gravity. How ...
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142 views

Potential Energy of Springs and Gravity, and Work of a force

I am currently really stuck on this problem and I am not sure how to actually solve it, I think I can reason it out logically but I do not know how to show it. Here it is and under I will show what I ...
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24 views

Throwing the object around the Earth [closed]

You have to throw an object to a point diametrically opposite od Earth surface, take that Earth does not rotate and that it is perfect sphere. What angle to the ground and velocity must object have? ...
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186 views

Equation derivation for skipping rocks

oWhy can rocks skip over water? For instance, if you conduct an experiment where you drop both rocks from the same height, but give one considerable acceleration in the x direction, one will fall in ...
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50 views

What fills the space between the galaxies, stars and planets? [duplicate]

What fills the space between the galaxies, stars and planets with the exception of gas clouds, dust, atoms, elementary particles and electromagnetic radiation? What the authoritative opinions exist on ...
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1answer
20 views

Is 0.1 bar (hydrostatic pressure) equivalent to 0.1 bar vacuum pressure (absolute pressure)?

Suppose we would like to test the ability of an objec to withstand the pressure under 1 meter of whater. I would like to understand how to simulate this situation using vacuum. Is the 0.1 bar (for 1 ...
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1answer
10 views

Lenghthwise center of gravity of a boat based on flotation angle

I am trying to determine the center of gravity horizontally along the length of a pontoon boat so I can properly position the load on my lift. Approximate will do. It seems like an impossible question ...
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33 views

Is the Universe a 4D elastic shell that is contracting with time, where particles are traveling waves or standing waves of energy density? [closed]

In gravitational red shift, “the phenomenon known as the red shift of a photon is really the blue shift of an atom.” This conclusion also applies to Galactic redshift. According to Hubble’s law, when ...
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Is electricty matter? [closed]

Electricity is a flow of electrons. I'm right until here, and matter is something that takes up space. (I can't be in the same place as my friend does). And correct me if I'm wrong but an electron ...
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86 views

Can gravity in principle be made to flow through a “wire”?

Electricity can be made to flow preferentially through a conductor such that a potential difference can be exploited and it can be used to do work remotely. In principle could an analogous "gravity ...
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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 ...
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46 views

“This Side Up” in Zero g?

I know that at a particular altitude above Earth, the effects of its gravitational pull become negligible- thus the feeling of weightlessness by astronauts. In most Sci-Fi movies, including the much ...
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27 views

Distance of closest approach

When deriving the gravitational bending angle of light, In this paper, the author introduced $R$ (the distance of closest approach), in equation ($7$), to solve the problem. My question: How is $R$ ...
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76 views

What is the binding energy in General Relativity?

In general relativity, the potential energy is given by $$V(r)=\frac{h^{2}}{2r^{2}}\left(1-\frac{2M}{r}\right)-\frac{M}{r}.$$ Solving $V^{\prime}(r)=0$, there are two points where circular orbits ...
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658 views

Velocity required for Horizontal Rain

Related to my previous question - Change in appearance of liquid drop due to gravity... Ok, I think we all have noticed this practical phenomena (a kind of illusion though)... During rain (while ...
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About spin 2, graviton, in the context of attractive force.

excerpt from Introduction to Black hole physics, Valeri P. Frolov and Andrei Zelnikov In this textbook, there is comment about spin of gravitons as follows For gravitating bodies the gravitational ...
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51 views

Choice of framing in Gravitational Chern-Simons

I was trying to understand formula(2.21) in Witten's paper "Quantum Field Theory and Jones Polynomial"(link: https://projecteuclid.org/euclid.cmp/1104178138) (Page 360). There, it was mentioned, the ...
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Swimming in a ball of water in space

What would I feel if I went swimming in a ball of water in space? Would I feel greater pressure as I went deeper into the sphere? What would it be like to swim in something like that? Also, let's say ...
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Isolation of a Physical System and Energy

I'm trying to grasp basic concepts of energy and i have a little doubt regarding conservation of energy. According to Feynman book and Wikipedia, the Law of Conservation of Energy states that ...
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246 views

Where does air pressure come from?

Where does air pressure come from? I thought it was from gravity or the speed of the gas resulting from its heat. However, analyzing my own hypotheses, I think that my 'heat conjecture' is probably ...
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805 views

What is the radius of the event horizon?

I know that the Schwarzschild radius is given by $$r~=~\frac{2GM}{c^{2}}.\tag{1}$$ However, If we had the metric $$ds^2~=~−A(r,t)dt^2+\frac{dr^2}{B(r,t)}+r^2(dθ^2+\sin^2{θ}dϕ^2),\tag{2}$$ where ...
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What is the difference between gravitation and magnetism?

If you compress a large mass, on the order of a star or the Earth, into a very small space, you get a black hole. Even for very large masses, it is possible in principle for it to occupy a very small ...
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127 views

Spiral galaxies and gravity lenses

Spiral Galaxies must have a great deal more mass than elliptical galaxies of the same size in order to account for the flat velocity curve. I've seen references of eight to ten times the visible ...
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136 views

How to derive the Schwarzschild radius? [duplicate]

I know that the Schwarzschild radius is given by $$r=\frac{2GM}{c^{2}}.$$ but I never seen a derivation for this equation. 1- Does anyone know how to derive this equation from general relativity? ...
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122 views

Physics of a cold and hot top

Imagine two tops made up of exactly one thousand atoms. One is kept at 4 degrees Kelvin, the other at room temperature. 1. Would they weigh the same given an arbitrarily precise scale in the Earth's ...
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41 views

Can pre-inflationary gravitational attraction affect objects after inflation?

According to inflation theory, the inflation itself took place at some short yet finite time after Big Bang, so there should be some gravitational interactions present before inflation, some objects ...
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129 views

Is the Universe being dragged into a singularity rather than expanding?

Recently I've read that the expansion of the Universe as observed is not exactly uniform as proposed by Hubble. Therefore is it possible that instead of space expanding in all directions all matter is ...
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1answer
65 views

Do gravational effects 'travel' through a wormhole?

Lets say a wormhole exists with point A inside the gravity well of a star and point B in a space where there is no notable nearby mass to create a gravitational force. If one were to approach point B, ...
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76 views

Geodetic effect and Frame dragging

Two gyroscopes pointing perpendicular to each other were housed inside Gravity Probe B which performed polar orbit around Earth to test Einstein's theory of relativity. As the probe is orbiting ...
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The age of black holes

I have a very small understanding of space-time however I have been watching some interviews and reading articles featuring theoretical physicist Kip Thorne and I have a few questions that I hope can ...
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7k views

Why does a parachute decrease terminal velocity?

Terminal Velocity depends on two things- surface area and speed. These are inversely proportionate. If both these variables affect terminal velocity, why do parachutes slow you down? Initially you ...
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Will a black hole cause scattering of a gravity wave?

In my GR textbook, it states that gravity waves can undergo interference but not scattering. I am just starting the chapter on linearised gravity concepts (weak field approximation) and my apologies ...
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Capillary effect to pump water up to cool water

Chinese scientists demonstrated anti-gravity pump, which uses capillary effect and super-hydrophobic screen to flow water upward by 1cm using internal energy of water. How much water will be cooled ...
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82 views

Gravitational potential in GR

In proving that the metric will play the role of gravitational potential, there is this chain of ideas: ...
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798 views

When space bends, what are the lines that are being bent?

In an electric field diagram, the lines represent the electrostatic force vector at the position. These lines are bent when you place a charge into the system. What is the equivalent description ...