Gravitational Definition and 1000 Threads

Gravity (from Latin gravitas 'weight'), or gravitation, is a natural phenomenon by which all things with mass or energy—including planets, stars, galaxies, and even light—are attracted to (or gravitate toward) one another. On Earth, gravity gives weight to physical objects, and the Moon's gravity causes the ocean tides. The gravitational attraction of the original gaseous matter present in the Universe caused it to begin coalescing and forming stars and caused the stars to group together into galaxies, so gravity is responsible for many of the large-scale structures in the Universe. Gravity has an infinite range, although its effects become weaker as objects get further away.
Gravity is most accurately described by the general theory of relativity (proposed by Albert Einstein in 1915), which describes gravity not as a force, but as a consequence of masses moving along geodesic lines in a curved spacetime caused by the uneven distribution of mass. The most extreme example of this curvature of spacetime is a black hole, from which nothing—not even light—can escape once past the black hole's event horizon. However, for most applications, gravity is well approximated by Newton's law of universal gravitation, which describes gravity as a force causing any two bodies to be attracted toward each other, with magnitude proportional to the product of their masses and inversely proportional to the square of the distance between them.
Gravity is the weakest of the four fundamental interactions of physics, approximately 1038 times weaker than the strong interaction, 1036 times weaker than the electromagnetic force and 1029 times weaker than the weak interaction. As a consequence, it has no significant influence at the level of subatomic particles. In contrast, it is the dominant interaction at the macroscopic scale, and is the cause of the formation, shape and trajectory (orbit) of astronomical bodies.
Current models of particle physics imply that the earliest instance of gravity in the Universe, possibly in the form of quantum gravity, supergravity or a gravitational singularity, along with ordinary space and time, developed during the Planck epoch (up to 10−43 seconds after the birth of the Universe), possibly from a primeval state, such as a false vacuum, quantum vacuum or virtual particle, in a currently unknown manner. Attempts to develop a theory of gravity consistent with quantum mechanics, a quantum gravity theory, which would allow gravity to be united in a common mathematical framework (a theory of everything) with the other three fundamental interactions of physics, are a current area of research.

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  1. AN630078

    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...
  2. AN630078

    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...
  3. AN630078

    Rearranging gravitational and centripetal equations to derive formulas

    1. Newton's Second Law states F=ma and the formula for centripetal acceleration is v^2/r Therefore, F= mv^2/r Would this be complete, I just feel that I should need to do something further but I am not sure what? 2.F=mv^2/r Gravitational force = GMm/r^2 Gravity is the cause of centripetal...
  4. AN630078

    Difference in Gravitational Potential on the Moon

    1. Since the gravitaional field strength is 1/6 of that on Earth: W=mg W=90*9.81/6 W=90*1.635 W=147.15 ~ 147 N 2. ∆Ep=mg∆h ∆Ep=90*1.635*50 ∆Ep=7357.5 J I do not now whether this method would be suitable and if I should have instead used the formula for gravitaional Potential, V grav=-Gm/r? 3...
  5. R

    B Gravitational Waves: Prevalence Across the Universe

    Would it be correct to say, that gravitational waves of the magnitude that is currently detected by LIGO and similar detectors, are prevalent to the extent that there is no single location in the known universe, that such magnitude of gravitational waves, don't pass through at least several...
  6. R

    B Measuring Gravitational Waves w/ Elevator Accelerometer

    An elevator in outer space where there is negligible gravity, accelerates at the most precise constant acceleration that current technology enables. Inside that elevator, resides an accelerometer that is the most precise accelerometer that current technology enables, but not more precise than...
  7. R

    B Gravitational Waves: A Question on Earth's Magnitude & Frequency

    Here is a video i have watched: It made me think of the following questions: A. Gravitational waves at the scale that emanate from earth: 1. It is doubtful if they exist at all. 2. They are predicted to exist, but at an extremely small magnitude. B. In case the answer is A2: 1. These...
  8. plomeiko

    Question about gravitational potential energy and angular motion

    hello I would like some help with the first part of this homework. for the moment i have done this: E initial=m*g*h Efinal= 1/2 m*v ^ 2+1/2I*ω ^ 2 Ei=m*g*h+1/2I*ω ^ 2 Ef=1/2*m*v ^ 2 my doubt is with the potential energy since it confuses me when there is or not...
  9. T

    B Gravitational Waves in Positively Curved Universe?

    Hello everyone! I was listening to a podcast that featured a cosmologist and she mentioned that if the universe was positively curved (and therefore a sphere overall), light would travel around the universe and then end up where it started. I wondered, would a gravitational wave do the same?
  10. snoopies622

    B Does E=mc^2 apply to gravitational potential energy?

    I'm reading Schutz's A First Course In General Relativity and in chapter 5 he discusses an idealized experiment in which an object is dropped from a tower, then turned into a photon and sent back up to its original height. In classical mechanics we would say that as the object falls it loses...
  11. M

    Gravitational wave source triangulation

    In my new novel, Handwavium, renowned genius physics Professor Samuel Clements Silver has created a prototype gravitational wave radio. For plot purposes, the protagonist needs to use the signal to triangulate his location. I know LIGO has three detectors and have seen reports of sources like...
  12. E

    How Does Gravitational Compression Generate Heat in Protostars?

    When I did this the first time I didn't really think too much about it, so I just wrote$$p = \frac{nRT}{V} \implies W = \Delta U - Q = - Q = -\int_{\frac{4}{3}\pi r_0^3}^{\frac{4}{3}\pi r^3} \frac{nRT}{V} dV$$That turned out to be correct, but when I thought about it I didn't understand why this...
  13. Hamiltonian

    Gravitational potential energy -- Why is it always negative?

    the gravitational potential energy of a body at any point is defined to be negative of the work done by the conservative force(gravity in this case) from bringing it to that point from a given reference point. if the reference point is taken to be at infinity and the potential energy at this...
  14. R

    B Detecting Gravitational Waves: Earth-Like Planet Possibility

    Is it theoretically possible that one day a gravitational wave detector will be developed, that is sensitive enough to detect gravitation at the order of magnitude that an Earth like planet has?
  15. Helena Wells

    I Mass of the Moon and Gravitational Lensing

    During an eclipse the Moon covers the Sun.However this shouldn't be happening due to gravitational lensing we should be able to see some light? Is the mass of the Moon not big enough or photons do reach us but they are so little our eyes can't detect them?
  16. Z

    I Gravitational Redshift: Units, Velocity & Ratio Explained

    I noticed in physics papers that gravitational redshift is expressed in m/s or km/s. I assume that this must be the equivalent velocity to produce that same redshift. So for example, if the gravitational redshift was measured as 3x10 ↑ -4 then; z= v/c 3x10^-4= v/c v = 9x10^4 m/s v=90km/s...
  17. Ranku

    Electrostatic and gravitational forces

    An object on the surface of the ground does not penetrate the ground. How much is this because of the electrostatic force between the particles constituting the ground and the object, and thereby maintaining their integrity? And, how much is it because of the materiality of the mass of the...
  18. R

    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?
  19. J

    B Gravitational Mass of C/2 Objects: Jim Adrian's Inquiry

    I would like to be sure that objects passing at high speed (half or more of the speed of light) have more gravitational attraction to each other than they would if their relative speed were forty miles per hour. Thank you for your help. Jim Adrian
  20. jaumzaum

    A Gravitational Energy: Field x Moment

    Hello! I was wondering if it is possible to express the gravitational energy as a product of the gravitational field by a moment, as we do with the magnetic and electric energy? Would this require the existence of bodies with negative mass? How could we relate this to the existence or total...
  21. pelinkovac

    I Gravitational Wave Creation: Is a Stationary Wave Possible?

    Hello, Apart from the graviton postulate, which would permit such a mechanism, my question is: would a similar mechanism be possible with a stationary wave? (the simplest scenario I can immagine is of two opposing waves). My background is in DSP and Acoustics so I might get things wrong (a...
  22. Paul Stowe

    I The Non Constant Gravitational Constant (G)?

    History & evidence can be found in: https://onlinelibrary.wiley.com/doi/full/10.1002/andp.201900013 https://phys.org/news/2015-04-gravitational-constant-vary.html {unacceptable reference deleted} The experimental data strongly suggest are actual x,y,z,t variations in the measured value of G
  23. marialovesphysics

    Gravitational potential energy formulas

    m.g.h = (GMm)/r how can we prove that mgh is potential energy and both equal to that?
  24. E

    B Gravitational Lensing & MOND: Does DM Explain Observations?

    Do gravitational lensing observations support the need for huge amounts of DM? If so, what do the MOND proponents say about that?
  25. P

    B Consequences of the Existence of Gravitational Waves?

    I'd like to see some of the consequences of the existence of gravitational waves (both expected and unexpected), in laymen's terms so a simpleton like me can understand and relate to them. A possible consequence that I thought of (and I'm sure someone will correct me if I'm wrong) is that...
  26. R

    Why gravitational potential energy is a system property?

    Spring has more potential energy when it is compressed or stretched from its initially balanced state. As external work is done, it stores energy in the form of potential energy. Here, we know energy is stored in spring but For the Earth-ball system, where the energy stored?
  27. R

    What is the reason that the Gravitational Constant (G) varies?

    If G really not a constant then what are the implications in science?
  28. sbrothy

    B Lensing Gravitational Waves Like Light?

    I was reading (or at least skimming) this paper: https://arxiv.org/abs/2005.10702 in which they seem to be discussing gravitational wave lensing. Is this an analogue of light lensing or is it another subject entirely? I mean, as I understand it, light is bend using gravity (as for...
  29. J

    Net Gravitational force on an object

    First, start off with x and y directional forces F (Test object 1) - F x(Test object 2) I need help primarily with finding the horizontal component of the force from object 2. How do I find it and express it? Thanks
  30. olgerm

    I Testing Gravitomagnetic Effect: Max Practical Results

    I was thinking about an experiment to demonstrate gravitomagnetic effect. I did my calculations using gravitomagnetic model. It is not as accurate as general relativity, but GR should give similar predictions. I do not know if it would be possible to to this experiment in real life(are there...
  31. E

    How will the equation for gravitational force be changed?

    At first, I thought when the rod goes really far away from the particle, then L would approach to zero in a particle's reference view. As a result, the equation will be GmM/d^2. However, I just thought that L just remain as it is regardless of change in d, but not sure...
  32. LCSphysicist

    What is the gravitational strength "G"?

    I am doing a book that have only exercises, and an introduction to the posterior theme, so, in the introduction, there is the relevant equations, and there is a equation: G = -Gm/r^3 called strength G, in the gravitational topic, what is this? I never saw it.
  33. J

    I Gravitational time dilation using an accelerating light-clock

    I've been trying to understand gravitational time dilation by considering a light-clock of length ##l## undergoing an equivalent acceleration ##a## from rest along the direction of the bouncing light pulse. I find that the time ##t## that the light pulse takes to travel to the forward receding...
  34. K

    I Using AI for Gravitational Wave Generation

    Hello! Can someone point me towards some papers that use AI for gravitational wave generation? I found many papers using AI to analyze data, but not really something where AI is used to actually generate waveforms. For example this was done for particle physics simulations to increase the speed...
  35. T

    Java Changing the Universal Gravitational Constant: A Java Applet

    Hello folks, I am working on Java program just for fun to model an n-body problem using 3-dimension graphics. I'm looking for a way to speed up the model. Suppose for example that I decide to increase the speeds of all objects by a factor of, say, 2. To compensate, I would also increase the...
  36. pinball1970

    I Gravitational lensing used to observe a distant galaxy

    The alert is here, https://www.sciencealert.com/supermassive-black-hole-jets-have-been-seen-slamming-into-gas-in-the-early-universe The abstract from the paper here, https://iopscience.iop.org/article/10.3847/2041-8213/ab7b7e The effects of jets from a black hole within the galaxy including...
  37. G

    A Moller Tetrad Gravitational Lagrangian: Limits on Lambda?

    This is a quite specific question, but maybe someone knows (part of) the answers, what would be much appreciated. The Moller (the o is a specific Danish character) Lagrangian for gravitation reads (see for example Aldrovandi-Pereira, Teleparallel Gravity, Springer 2013) ##L = \partial_\mu...
  38. Yassin98

    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...
  39. cianfa72

    I Gravitational time dilatation and curved spacetime - follow up

    Hi, starting from this very interesting thread I'm still a bit confused about the conclusions. The main point, as far as I can understand, is all about conditions for a quadrilateral to be considered a parallelogram. My first basic doubt is: the concept of 'parallel' applies just to geodesic...
  40. T

    I The existence of negative gravitational plus positive inertial mass?

    The term “negative mass” gets puts forth occasionally, and it’s definitions can sometimes be unclear. the topic I’m interested in is particles which have both positive inertial mass and negative gravitational mass. So far, what theories do physicists have of speculating on the existence of...
  41. jamiebean

    Is Gravitational Acceleration Positive or Negative in Upward Motion Problems?

    I attempted the question with d=vi x t + (at^2)/2 gravitation acceleration= -9.8 and I got the solution of 22.724. Should I use the value of -9.8? or should I just use 9.8? should I use the equation above? I feel like what I am calculating is not displacement but distance... thank you
  42. T

    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?
  43. V

    Tension forces of two wires in comparison to the gravitational force

    The correct answer is the second one. I honestly have no idea why this is so. I understand that the right rope has less tension that the left one since it's at a shallower angle from real world experience, but I don't really know why this is so, let alone how the forces compare to gravitational...
  44. John10086

    Irodov problem 1.12 — A 3-body gravitational attraction problem

    The thing is, I've already looked up at the solution online at it's t= 2a/3v. But I've approached it a different way and I can't really tell what I'm doing wrong, my solutions gives out t= (a/√3v )* (π/3),I don't know what's wrong with it. Here's my approach: The points will meet at the...
  45. F

    Stargazing Is a star's size changed due to gravitational deflection (lensing)?

    Using the Sun as example, we know from the Eddington experiment that the Sun deflects light. Does light from other stars get deflected towards or away from the centre of mass, or is it a mix? Does light coming from the Sun get deflected towards or away from the centre of mass? Would this make an...
  46. B

    Finding distance between Earth and Moon in gravitational fields

    Here are 2 questions that I have tried to answer and was hoping if these are right ways to go about it? Q1) Find the distance in meters (m) between centre of the Moon and the centre of the Earth, assuming that the Moon moves in a circular orbit with a period of 27.5 days. Take the mass of the...
  47. Athenian

    [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...
  48. Staticboson

    I Inertial frames in changing gravitational fields

    The man floating inside the elevator travels through space at constant velocity, and soon reaches proximity to a planet. To an outside observer, the elevator appears to change course and accelerate towards the planet, so he reasons there is a force acting on the elevator, changing its course and...
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