# What is Gravitational field: Definition and 369 Discussions

In physics, a gravitational field is a model used to explain the influences that a massive body extends into the space around itself, producing a force on another massive body. Thus, a gravitational field is used to explain gravitational phenomena, and is measured in newtons per kilogram (N/kg). In its original concept, gravity was a force between point masses. Following Isaac Newton, Pierre-Simon Laplace attempted to model gravity as some kind of radiation field or fluid, and since the 19th century, explanations for gravity have usually been taught in terms of a field model, rather than a point attraction.
In a field model, rather than two particles attracting each other, the particles distort spacetime via their mass, and this distortion is what is perceived and measured as a "force". In such a model one states that matter moves in certain ways in response to the curvature of spacetime, and that there is either no gravitational force, or that gravity is a fictitious force.Gravity is distinguished from other forces by its obedience to the equivalence principle.

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1. ### B How does gravitational field exert gravitational force on a body?

I am not sure if there is in fact a classical description of how it occurs, but I’d like to know if there isn’t too!
2. ### I Potential energy and the gravitational field of a collapsing cloud of gas

Imagine an empty void of intergalactic space. In this space there is a cloud of diffuse gas, mostly hydrogen and helium. The gas is non-rotating and very cold just above absolute zero. There is nothing else around this cloud, and so it has a clear center of gravity, and no other objects...
3. ### I Connection b/w curvature and gravitational field-removing coordinate transformations

I'm studying Susskind's GR TTM book, in which he gives a nice explanation of why differential geometry is needed for GR. But there is one gap that I want to fill. The argument is: through a thought experiment, it seems that a uniform gravitation field can be seen as an artifact of going from an...
4. ### I Congruent worldlines in "static" gravitational field

I'm reading Carroll's GR book and can't quite understand one particular statement. I'll summarize for context: There's a tower with a physicist at the base and one at the top. Ground guy emits a beam of light with wavelength ##\lambda_0## from height ##z_0##, which travels to the top of the...
5. ### I Gravitational field modulation of a moving mass

If a mass is moving it has a wavelength - my question is, is the gravitational field of the mass then modulated accordingly ?
6. ### Gravitational equipotential multiple choice problem

Hello everyone, thank you for taking your time to read this. I was assigned a homework task of multiple choice questions to do with gravitational fields. This is one of the last questions and I have been pondering over it for some time now. I don't understand how any sort of answer is...
7. ### I Gravitational Field Existence in Void: Philosophical Inquiry

This is of a more philosophical inquiry. If two particles are in a void and moving apart, if they are sufficiently far apart, like say the distance between two galaxy cluster walls, does the gravitational field between them still fundamentally exist? I'm trying to understand if gravity will...
8. ### A Static Gravitational Field: Why Must ##g_{m0} = 0##?

In Dirac's "General Theory of Relativity", he begins Chap 16, with "Let us consider a static gravitational field and refer it to a static coordinate system. The ##g_{\mu\nu}## are then constant in time, ##g_{\mu\nu,0}=0##. Further, we must have ##g_{m0} = 0, (m=1,2,3)##." It's obvious that...
9. ### I Time Dilation in Gravitational Field: Potential vs Field Strength

I'm wondering is whether it is the gravitational potential (in J/kg) at a point in space that determines the rate of passage of time, or whether it is the gravitational field strength (in m/s2). To clarify, suppose you had a very heavy hollow spherical shell. The gravitational potential would...
10. ### A Exploring the Electric Field of a Moving Charged Spherical Shell

The electric field inside a charged spherical shell moving inertially is, per Gauss's law, zero. If the spherical shell is accelerated, the field inside is not zero anymore, but it gains a non-null component along the direction of the acceleration, as mentioned, for example, in this paper. The...
11. ### Gravitational field of a hollow sphere

Why the area of the thin rings are ##2πasin\theta \, ds##? (a is the radius of the hollow sphere) If we look from a little bit different way, the ring can be viewed as a thin trapezoid that has the same base length ( ##2πa sin\theta##), and the legs are ## ds##. The angle between the leg and...
12. ### I Uniform gravitational field possible in GR?

Mentors’ note: this thread is forked from https://www.physicsforums.com/threads/free-fall-in-curved-spacetime.1016510/ But what if the gravity field is homogeneous? Like that of an infinite massive plane? The objects in the ship will stay where they are. An infinite massive plane is quite...
13. ### I Postulating a minimum gravitational field strength

this paper postulating a minimum gravitational field strength postulating a minimum gravitational field strength (minimum curvature) and a minimum acceleration but otherwise leaving Gr could reproduce MOND [Submitted on 25 May 2022] MONG: An extension to galaxy...
14. ### I Acceleration at 1g in space -- Does it create a gravitational field?

Does a body accelerating at 1g in outer space create a gravitational field around it ?
15. ### I Gravitational Field with Dark Energy: Observable Effects?

since the cosmological constant observed is that there is a small amount of energy in empty space, and in general relativity anytime there is energy there is curvature and therefore gravity, how to calculate gravitational field with dark energy and does it have any observable effects on matter...
16. ### Gravitational Field and Potential at certain point

The removed mass is ##\frac{1}{8}M## My idea is to find ##g## from large sphere then minus it with ##g## from small sphere (because of the removed mass): ##g## at A = $$\frac{GM}{R^3}\left(\frac{1}{2}R\right)-\frac{G\left(\frac{1}{8}M\right)}{R^2}$$ Is this correct? Thanks
17. ### B A question from Resnik about g-force

Suppose there is one force gravitational force ##\vec{f_g}##. We can relate this downward force and downward acceleration with Newton sec law. This law can be written as ##F_{net,y}=ma_y## which becomes $$-F_g=m(-g)$$ or $$F_g=mg$$ $$\vec{F_g}=-F_g \hat j=-mg \hat j=m\vec g$$. Is it right...
18. ### I Gravitational Field of Electromagnetic Waves: How is it Generated?

Hi ! It catches my attention that atomic particles such as protons, neutornes, electrons and their respective subparticles such as Quarks are theoretically formed by high-energy electromagnetic fields such as gamma rays and then the gravitational field that would generate the mass of these...
19. ### I Rindler Transformation & 't Hooft's Introduction to General Relativity

I am reading 't Hooft introduction to general relativity. https://webspace.science.uu.nl/~hooft10 ... l_2010.pdf In this text 't Hoof derives the Rindler transformation. A little bit further he writes My question is, how does he come to that formula $$\rho^{-2}g(\zeta)$$
20. ### B Maxwell-Boltzmann distribution under the influence of a gravitational field

Could anyone suggest a simple video showing the Maxwell-Boltzmann distribution under the influence of a gravitational field? I trying to show a flat earther idiot how pressure gradients arise in a simple manner. Thank you all. DF
21. ### Find the gravitational field strength of planet X

weight/mass = gravitational field strength. my working is -> weight = 150kgx10m/s² = 1500N mass = 150kg gravitational field strength= 10N/kg. is this correct?
22. ### I Weak Gravitational Field & Wave Eq. - Analyzing Effects on Massless Scalar Field

A massless scalar field in a curved spacetime propagates as $$(-g)^{-1/2}\partial_\mu(-g)^{1/2}g^{\mu\nu}\partial_\nu \psi=0 .$$ Suppose the gravitational field is weak, and ##g_{\mu\nu}=\eta_{\mu\nu}+\epsilon \gamma_{\mu\nu}## where ##\epsilon## is the perturbation parameter. And let the field...
23. ### A Gravitational field of an infinite flat slab

Off the back of a recently closed thread where there was some discussion about the gravitational field of an infinite flat slab, I decided to have a play at investigating that. I've found a few interesting things. It's fairly straightforward to solve for this situation. You use Cartesian-esque...
24. ### Non-interacting gas in homogeneous gravitational field

It even gives a hint, it says "consider two horizontal surfaces z1 and z2 and think about what thermodynamic equilibrium means for particles traveling from one surface to the other". This really trips me up because I am not sure what to do with this. Obviously in equilibrium the number of...
25. ### A The g_ij as potentials for the gravitational field

The equation of motion for a particle in a gravitational field is ai = -Γijk vj vk In inertial coordinates the Lorentz force is mai = qFij vk So it seems like F corresponds to Γ. Just like F is expressed in terms of the derivatives of A, the christoffel symbols are expressed in terms of...
26. ### Gravitational Field Multiple Choice Help

1. I believe that the gravitational field strength would decrease because it is inversely proportional to the square of the distance from the centre of the Earth, g∝1/r^2. Gravitational potential energy at large distances is directly proportional to the masses and inversely proportional to the...
27. ### Gravitational Field Strength at the equator and poles

1. The centripetal force is equal to F= mv^2/r. The velocity of the Earth can be found by: V=2πr/T T=1 day = 24 hr*60min*60sec=86400 s v=2π*6.4 x 10^6/86400 s v=465.4211 ... ~465 ms^-1 to 3.s.f Therefore, F=1*465/6.4 x 10^6 F=98/1280000=7.265626 *10^-5 ~7.3 *10^-5 N Would this be correct since...
28. ### B Gravitational Field Representation: Why 1-Plane?

How did you find PF?: Surfing web Can someone advise on this? In most diagrams showing how mass effects the gravitation field (earth for instance), bending fabric of space, it is demonstrated on one plane. Why is it shown this way and is there any other way of illustrating this?
29. ### The Equivalence Principle -- Is this a way to distinguish between a gravitational field and an accelerated rocket?

If we are in a cabine in a gravitational field and inside, we have a racket and a ball. We put strings in each side of the racket and we connect the racket to the ceiling of the cabine. This strings only allows us to keep the weight of the racket. Then, we drop a ball to the racket. We do this...
30. ### I Electromagnetic Radiation in Strong Gravity Field

Does the electric and magnetic fields of electromagnetic radiation remain perpendicular in the presence of an intense gravity field? If not, what is the physical ramifications of this?
31. ### [SR] - Test Particle inside the Sun's Gravitational Field - Part 4

So, here's an attempted solution: With ##r_{min}##, $$r_{min} = \frac{1}{B + \frac{\beta}{\alpha^2}}$$ With ##r_{max}##, I get: $$r_{max} = \frac{1}{B - \frac{\beta}{\alpha^2}}$$ or $$r_{max} = \frac{1}{\frac{\beta}{\alpha^2}}$$ Other than this, I and the team have absolutely no idea on how...
32. ### [SR] - Test Particle inside the Sun's Gravitational Field - Part 3

Below, I have already solved - I assume - correctly for question 1. Question 2, I am nearing to what I believe is the solution. Question 3, I simply have no idea where I should begin considering that it is interconnected with question 2. With that said, below is the lengthy and somewhat tedious...
33. ### [SR] - Test Particle inside the Sun's Gravitational Field - Part 2

To begin with, I posted this thread ahead of time simply because I thought it may provide me some insight on how to solve for another problem that I have previously posted here: https://www.physicsforums.com/threads/special-relativity-test-particle-inside-suns-gravitational-field.983171/unread...
34. ### [Special Relativity] Test Particle Inside the Sun's Gravitational Field

Below is an attempted solution based off of another user's work on StackExchange: Source: [https://physics.stackexchange.com/questions/525169/special-relativity-test-particle-inside-the-suns-gravitational-field/525212#525212] To begin with, I will be using the following equation mentioned in...
35. E

### Working out the kinetic energy of a body due to a gravitational field

Usually when setting up an energy equation I use the general form, (Initial KE) + (Initial PE) + (Any other work done to the body) = (Final KE) + (Final PE) ... For this I said the initial GPE and KE are 0, and the work done by the field is GMm/x (derived by integrating a force of -GMm/r^2 from...
36. ### I Invariant Mass in Gravitational Fields: Special Relativity

In Special Relativity, you learn that invariant mass is computed by taking the difference between energy squared and momentum squared. (For simplicity, I'm saying c = 1). m^2 = E^2 - \vec{p}^2 This can also be written with the Minkowski metric as: m^2 = \eta_{\mu\nu} p^\mu p^\nu More...
37. ### B Propagation of changes in a gravitational field

I thought gravitational waves were how changes in the gravitational field was propagated. The Insight https://www.physicsforums.com/insights/how-fast-do-changes-in-the-gravitational-field-propagate/ says so as well. What got me confused was the following scenario: take a stationary black hole...
38. ### I Gravitational field versus acceleration

Would it be possible for a person in a lift to know if he is in a gravitational field if he measures the gravitational acceleration at the bottom of the lift versus the top as they would differ since gravitational field strength would be different between the bottom and top. In an accelerating...
39. ### B Does the mass of an object increase in a gravitational field?

From a frame of reference outside of a gravitational field, does the mass of an object near a gravitational field increase?
40. ### I Gravitational field in the galaxy and Schwarzschild´s time dilation

Is it possible to estimate the gravitational force of the center of a Galaxy (it could be Andromeda or the Milky way) to any point (such as a planet) of its Orbit? Furthermore is there such as Schwarzschild solution that calculates the time dilation of any point of an external Galaxy (e.g...
41. ### I Problem with gravitation field perpendicular vector.

since it is known that ##\vec{A_\perp} = -{mG \over R^2}## why did the professor write it as ##\vec{A_\perp} = {- R G \rho \over 3}## for perfect sphere with perfect mass distribution ? Shouldn't it be ##\vec{A_\perp} = -{4 \over 3} \pi R G \rho##? I need help thanks.

This paradox may have come from Feynman's Lectures on Physics, or I may have dreamed it up myself. I am not sure. It has been around for a while and if you have already seen it, I apologize. I am not aware of any resolution. An electron is at rest in a gravitational field. We know from...
43. ### I Time Dilation: Does Gravitational Field Strength Matter?

Hi I have 2 questions. There are 2 planets and one clock on each of them. One of them has a bigger gravitational field strength. And two clock have same distance from the core. 1-) Does time dilation occur between two? Which clock ticks slower? 2-) If time dilation occurs, which formula...
44. ### Calculating Magnetic Flux Density for an Electron Orbiting Near Earth's Surface

I've been given a question to find the magnetic flux density of the Earth if an electron is orbiting near to the surface. The answer to the question makes the magnetic force equal to the centripetal force and solves for B from there. However, I am confused to why the gravitational force has no...
45. ### Calculations based on Neutrons in a Gravitational field

Hello everybody! I am TanX. I was reading about neutrons in a gravitational field, which was based on the Grenoble experiment ( Institute Laue - Langevin ) conducted in 2002. I have put a link down here to the research papers below ( Refer to page number 17 in the booklet for the important...
46. ### I Unruh temperature in gravitational field

According to the Unruh effect an observer who is has an acceleration ##g## will observe the temperature of the vacuum to be $$T=\frac{\hbar g}{2 \pi c k_B}.$$ According to the equivalence principle the observer should measure the same Unruh temperature if he is sitting on a planet whose surface...
47. ### How Does a Plane Wave Affect the Metric in a Weak Gravitational Field?

Homework Statement Show that a plane wave with ##A_{xy}=0## (see below) has the metric ##ds^2=-dt^2+(1+h_+)dx^2+(1-h_+)dy^2+dz^2##, where ##h_+=A_{xx}sin[\omega(t-z)]## Homework Equations ##h_{\mu \nu}## is small perturbation of the Minkowski metric i.e. in the space now ##g_{\mu \nu} =...
48. ### I Gravitational field seen be relativistic particle

The gravitational field of some massive body appears one way to a nearby stationary particle. But does the field appear to be distorted to a particle traveling at relativistic speeds?
49. S

### Derivation of an expression for centripetal acceleration

Homework Statement I have derived the expression for the velocity of the satellite v= root of GM/r however I'm struggling to derive an expression for the centripetal acceleration of a satellite orbiting Earth. Homework EquationsThe Attempt at a Solution I'm not entirely sure which equations to...
50. M

### Mass and kinematics -- motion of objects in a gravitational field

does mass affect the motion of the vertical upward, vertical motion down, free fall motion, and parabolic motion?