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Questions tagged [gravity]

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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Does Graviton bend light?

In the weak gravitational regime where the low-energy effective action holds,(linearized) gravity can be quantized, and we can treat graviton as quantum fields on a Minkowski background. One can also ...
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Does the heat created by gravitational energy cause Infinite energy?

As everyone knows there is this thing called geothermal energy. Many people in Iceland and such countries get their energy from geothermal plants. My question is since some of the heat in the earth is ...
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How does the momentum conservation law hold for gravitational interactions in special relativity with Newton's third law being invalid?

Griffiths' argument that Newton's third law is invalid in special relativity The selected answer to the post above talked about momentum conservation in electrodynamics – Newton's third law ...
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How much pressure does the water ring exert on the spacecraft when gravity is generated by rotation?

We all know that the rotating spacecraft will generate artificial gravity. If there is a water ring along the wall of the spacecraft, the width of the water ring is b, the depth of the water ring is H,...
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How to calculate the volume resulting from mixed materials [on hold]

How can we calculate the volume of mixed materials? For example, if I mix 1000 grams of wheat flour with 750 grams of water, what would the volume be then?
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Metric for a Collapsing Disk and FLRW

I have to obtain a time-dependent metric for a disk which satisfies a simple differential equation but I am stuck with making sure that the physics is correct. To be explicit, I'll first describe a ...
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Question (mostly) About Relativity

Before I get into the actual question, I'd like to say that my only knowledge on Einstein's Theory of Relativity (both Special and General) have been obtained through about an hours worth of videos ...
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Doubt about energy conditions: the Time-like Convergence Condition

First of all, consider a congruence of smooth time-like geodesics parametrized by proper time $\tau$. So, a tangent vector to a time-like geodesic is indeed a four-velocity up to a factor constant; ...
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How can a system of Atwood machine lose gravitational potential energy?

The heavier block in an Atwood machine has a mass twice that of the lighter one. The tension in the string is 16.0 N when the system is set into motion. Find the decrease in the gravitational ...
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Using two simple pendulums to estimate $g$

I know that using the period expression for a simple pendulum we can have an estimation of the acceleration of gravity $g$. I encountered the following question One way of measuring the terrestrial ...
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Kinematic aspects of quantum gravity

Quantum gravity proposals at the leading perturbative order, such as the quantisation of linearized gravity, or the low-energy effective action like in string theory, provide the dynamics for the ...
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Gravitational force between large square plate and spherical object touching the plate [on hold]

How do I calculate the gravitational force between a very large square plate object and a small sphere touching that plate? I am assuming it is some kind of integration exercise but my mathematics is ...
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Insert sensors in an aerostat with helium?

Hy is possible for you insert sensors (to calculate pressure and temperature) inside an aerostat with helium ? I ask this because... I have an helium balloon anchored to the ground by a rope with a ...
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Derivation of Komar formulae from ADM formalism?

Is there a way to derive the Komar formulae from the ADM formulae? Both the formulae give the same answer for mass and angular momentum, so I was wondering if one can be derived from another. On an ...
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Can we define gravity on Calabi-Yau manifolds?

I have read about applying Hermitian geometry in general relativity in deriving holomorphic gravity. But if we take it some steps further i.e. allowing Kähler manifolds with the Ricci flatness ...
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Which way would objects, inside a container falling through earth's atmosphere, move, relative to the container?

Say, a sealed hollow container with 1 atm air pressure inside, is falling through earth's atmosphere. It is falling steadily with one side always facing the ground (Front Side) Inside the container, ...
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Casimir Vacuum Energy and the Sakharov Correction for Virtual Particles

There already exists a geometric interpretation in the Casimir equation for vacuum energy since it contains an area: $$\frac{F}{A} = -\frac{d}{dR} \frac{E}{A} = -\frac{\pi^2 \hbar c}{240 R^4}.$$ Can ...
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Bivector Gravity and d'Alembertian

Just wanting to check with the community if they can spot anything wrong with the following. First of all, let's quickly rehash the main equation, I arrived at independently for a construction of ...
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Physical Distance Calculation [closed]

Given that the redshift at recombination is $$z_R = \frac{a_0}{a_\text{R}} - 1 \approx 1096.41\quad\Rightarrow\quad z_R + 1 = \frac{a_0}{a_\text{R}} = 1097.41$$ If I have the physical distance of ...
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What is the value of $g$ at height 10 mile above from earth? [closed]

What is the value of $g$ at height 10 mile from Earth's surface?
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Stacked or focused gravitation [closed]

If there is such thing or concept stacked or focused gravitation? By this I mean that bodies who has gravitation themselves when put together with another body have sinergie on theyr gravitation wich ...
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Friction of a body [closed]

A body of mass 2kg is on point of slipping down a plane which is inclined at 15° to the horizontal. What force parallel to the plane will move from the plane?(g=10m/s²)
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How gravity really works in 3D and how and massive object attracts another object? [duplicate]

space is 3d then how an massive object creates curvature in 3d an how another object falls into that 3d curvature also if you are answering plese show an image of it.
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Does a body experience no decrease in its deceleration when it moves freely upwards in the earth gravitational field? [closed]

In the earth gravitational field: (a)Work is done when a force moves its point of application around a closed point (b)Bodies repel themselves when they come close (c)Energy is released when an ...
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Null Kruskal Coordinates and affine parameterization

Let $(M,g)$ be the Schwarzschild spacetime. The usual metric tensor in Schwarzschild coordinates reads: $$g=-f(r)dt^2+f(r)^{-1}dr^2+r^2d\Omega^2\quad f(r)=1-\frac{2M}{r}.$$ Now consider radial null ...
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Why this constant is included in the tortoise coordinate?

In the Schwarzschild spacetime, the tortoise coordinate $r_\ast$ is defined by the property that $$\dfrac{dr_\ast}{dr}=\left(1-\dfrac{2M}{r}\right)^{-1}$$ Now, we cam integrate this. Multiply by $r$ ...
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Is this PR Letter suggesting that sound transports mass, or only that it can be a source of gravitation?

Question: Is the point of the letter that sound can transport mass, or only that it can be a source of gravitation? The Phys.org article More evidence of sound waves carrying mass says: Using ...
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What Is The Connection Between The Planck Force And Black-holes? [duplicate]

This question deals with a unique case where the gravitational force at the event-horizon of a Black-hole can be expressed by The Planck Force acting at the boundary of a Schwarzschild envelope. If ...
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How similarly are light and matter affected by gravity?

For a path of travel in a shape that is straight before it curves, if the curvature of the path is attributable to gravitational force, what additional information (if any) would be capable of ...
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Gravity breaks Newton's third law?

Consider a thought experiment where there is a point mass M present in empty universe. Then another point mass m materializes (This is ONLY a thought experiment) at a distance of 1 light year from M. ...
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Why $g$ on equator is less than $g$ on poles? [duplicate]

I found this on my physics book. The book says $g$ on equator 9.78 $m/s^2$ and on the poles 9.81 $m/s^2$. Is it due to gravity?
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What is the direction of gravitational constant?

Our book says: $$\vec F=\dfrac{GMm}{r^2}$$ If Force is a vector quantity, $G$ must also be vector quantity so what is the direction of $G$. I am a school kid please explain simply and kindly
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What would be the time dilation standing on a neutron star in comparison to earth?

What would be the combined gravitational and velocity time dilation one would experience if they stood on the surface of a neutron star in comparison to standing on the earth's surface? Specifically, ...
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Quantum gravity: How do we know gravity operates at quantum scales? [duplicate]

Edit: An alternate angle on the original question I asked below: Would general relativity still create singularities in special cases (center of black holes) if we assumed that gravity had a lower ...
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Einstein field equations in terms of invariants [duplicate]

Is it possible to express Einstein field equations of general relativity in terms of invariants of Riemann tensor and Stress-energy tensor? I suppose field equations should lead to an algebraic ...
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Is there a Geometric Algebra for gravity?

I have been reading a lot on geometric algebra. I came to ask whether we had a formula for gravity under this algebra? - it turns out that an electromagnetic geometric algebra does exist but I could ...
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Calculating Inital Velocity required to stablize an orbit of a moon

I am currently attempting to create a little solar system simulation and I was curious if there's a decent way to calculate what a moon or planet's initial velocity would need to be to remain in orbit ...
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Does theoretical physics suggest that gravity is the exchange of gravitons or deformation/bending of spacetime?

Throughout my life, I have always been taught that gravity is a simple force, however now I struggle to see that being strictly true. Hence I wanted to ask what modern theoretical physics suggests ...
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Gravitation inside spherical hole in universe

I was doing a little thought experiment and ran into a paradox. How to compute the gravitational field inside a spherical hole in a universe that is otherwise filled with uniformly distributed mass? ...
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A bullet fired at a pendulum

I am taking a first year undergrad physics class (waves & modern physics), and the answer my book gives to the question bellow has left me a bit confused. Here is the question (excuse me if it’s ...
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Would a massive graviton emit more massive gravitons?

In the theory of massive gravity, suppose that two bodies start interacting by exchanging gravitons. Wouldn't these gravitons, having mass, have to exchange gravitons between themselves, with these ...
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Is it true that when you accelerate due to a non-gravitational interaction gravity is pulling you in the direction opposite to the acceleration?

We don't feel acceleration when we are only in a gravitational field due to equivalence principle as I understand it says gravity is simply inertia in spacetime. Is there any other type of force ...
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Now when we can measure gravitational field, how does the principle of equivalence hold true?

LIGO measured gravitational field waves. The whole thought experiment of Einstein, leading to ‘principle of equivalence’, assumes that there is no way to know inside the rocket that whether its ...
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Pressure on the outer hull of aeroplane on theoretical emergency landing

I'm trying to figure out the proper way to calculate the pressure on the hull of aeroplane when landing on water. Let's say the horizontal velocity of plane is $1000$ km/h and it starts free-falling ...
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What is the relationship between spin network spacetime and tensor network (entanglement) spacetime?

In 1971, Sir Roger Penrose, suggested a combinatorial construction of spacetime using the angular momentum of particles. This work led to and introduced the idea of spin networks which are ...
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Can a proton and an electron annihilate in a gravitational field?

According to this Physics.SE comment, it is gravitationally allowed, though very unlikely, for a proton and an electron to annihilate yielding two photons. Is that correct? If so, why? (In ...
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Unification of gravity and electromagnetism

Have there been any attempts at unifying gravity and electromagnetism at least at classical level since Hermann Weyl's idea of gauge principle (1918)? We now have Standard Model which is very ...
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Need help with Gauss Bonnet gravity

I am trying to find the equations of motion for a coupling Gauss-Bonnet gravity. The action is : \begin{equation} S=\int{d^4x \sqrt{-g}\left[\frac{R}{2k}+f(\phi)(\alpha R^2+\beta R_{\mu\nu} R^{\...
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Experimental proof of length elongation due to gravitational field?

In general relativity we see that length around a massive object is elongated due to its effect on the geometry of spacetime which elongates the length due to stretched space time. Is there any ...
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Reasons for not experiencing a force of attraction by the objects around us [duplicate]

When every body in the universe attracts other body, why do not we feel the force of attraction by massive buildings around us?