Gravity Definition and 1000 Threads

Inverse square law would reduce the gravity from the parts of Earth that are farthest from our feet. It'll also reduce the gravity from Earth's center by a lesser amount, but would that be lesser enough so the gravity 20 kilometers under our feet is stronger than the core's gravity or even the...

Quantum decoherence. and the emergence of continuous space/time and gravity In another forum I have experienced a lot of combative dialogue asserting that continuous time/space is a property of the smallest Quantum scale. My present knowledge indicates this not true, and that the goal of the...

Hi, you all, I have been for a couple of semesters interested in quantum gravity as a problem, but truth is I never have been properly introduced to any of the candidate theories. Actually, there are multiple candidates and I would like to compare them. The question then is the following: do...

Shouldn't work be minus when the man climbing up and force on him is down? shouldn't the power be also in minus? Can someone explain to me why is it positive please!

Can the energy of a gravitational wave be related to Plancks constant?

Hello friends of the Forum. I want to ask you why the inertial acceleration in free fall in the relativistic geodesic equations is assumed equal to zero in free fall and equal to 9.8 m/s at rest on the earth's surface. On the other hand, assuming that zero acceleration in free fall, what would...

[Mentors' note: No template because the thread was moved from the technical forums] TL;DR Summary: I need help with determining the value of 'g' using the data I have collected in the lab, using an apparatus consisting of light gates fixated on a stand, the positions of which can be varied...

Many explanations out there for gravity. One that I saw a few months ago explained that our gravity hete on earth is space moving toward the center of the earth, and we should be falling to the center of earth at a rate of 9.8 m/ s/s. But the surface of the earth is in the way... What happens to...

I can't find the answer anywhere here's my question. can a centrifuge exist outside a field of gravity. More specifically, in a theoretical void of nothing without stars in view or any point of reference for comparison how could motion like spinning or acceleration exist?

I began by drawing a diagram and resolving the forces. Since the question asked for 'apparent gravity' I tried to find the normal force. I started with the equations: $$\\(\frac{GM}{R^2}-N)sin\lambda-Fsin\lambda=m\omega^2Rcos\lambda$$ $$\\(\frac{GM}{R^2}-N)sin\lambda-Fcos\lambda=0$$ Solving...

Based on the fact of observed cosmological redshift, scientists have proposed different ideas to explain. One interesting question is whether gravity does negative or positive work now: According to universe expanding in Big Bang theory (Lemaitre, 1927), obviously gravity does overall negative...

Hello, I am attempting to work through problem 12.6 in MTW which involves formulating Newtonian Gravity using Curvature as opposed to the standard formulation. This is a precursor before standard GR. In it he states that the curvature tensor in this formulation is as follows...

It didn't work and I don't know how to do it.

Assuming dark energy is fairly, uniformly distributed through out the cosmos, how strong is it, or how much energy is associate with it, out in the deepest, emptiest voids in space? I'm specificlaly refering to the great voids in between the great walls of galaxy clusters. I'm making the...

Homework Statement:: Model for Gravity Relevant Equations:: Rg -Rg = G/(8pi*c^4)T The rubber table model for gravity can't quite translate to reality. One sees that a ball placed on the table distorts it, but this is due to it being in a uniform gravity field. Just what mechanism distorts...

This might sound as a dumb and silly question but if you think about it, it makes sense. If we wrongly assume that gravity is a force just like any other, and given the fact that time is closely related to gravity and that gravitational time dilation is a thing, wouldn't reverse time travel...

Since gravity accelerate things (even with some people saying that it's not a force) there must be a consense that it adds energy to things. There are even hydroeletric power plants generating energy everywhere. So where does the energy of gravity come from? Is it spontaneous generation of energy?

Surface acceleration is proportional to density and radius of planet (as 2 powers of R cancel with the volume) g(moon)/g(earth) = density(moon)*radius(moon)/density (earth)*radius(earth) = (1/4)*density(moon)/density(earth)

Can anyone tell me how to solve this problem? I have the stem of a tree that is X feet tall. It's just a cylinder as the top and all branches have been cut off. I want to cut off the top portion such that when it falls, it will do precisely a 3/4 rotation and land perfectly flat. What fraction...

For story purposes, I want a portal from the Earth to a sealed cave on the Moon. But how would gravity behave near such a portal? A test mass on the moon end feels 1.6m/s^2 acceleration towards the center of the Moon, a test mass on the Earth end feels 9.8m/s^2 acceleration towards the center...

IIRC, the Sun's gravity was calculated by Einstein et-al to provide a 'focus' about 550 AU out. Current value is ~542 AU. Aside from effects due solar oblateness, frame dragging etc, may I assume this value also applies to eg neutrinos, gravitational waves etc etc ??

Einstein showed (via general relativity) that spacetime is curved by mass, mass moves in relation to this curvature, and that gravitation arises as secondary effect. Why then are we looking for quantum gravity as some sort of mass<->mass interaction? Aren't the fundamental interactions better...

I listened to and quite liked Sabine Hossenfelder's recent vid on relativity. Though one thing struck me as wrong. "Gravity is not a force," so it's effects does not cause true acceleration, so it has no effect on time. OK, but I'm pretty sure that satellites in different orbits have...

...y and Coulomb's law diverge as ##r\rightarrow##0? I mean, if a point light source emits light omnidirectionally, the intensity converges at the source, right? THIS is how I should've worded my previous post!

I was reading this paper (*Green's functions for gravitational waves in FRW spacetimes:* [https://arxiv.org/abs/gr-qc/9309025](https://arxiv.org/abs/gr-qc/9309025)) and I had a specific question about one statement in the paper that I would like to ask: At page 6, the author says that...

When we throw a ball in a projectile motion, the ball follows a parabolic path due to gravity. And we see that earth moves in an elliptical path around the sun due the same force of gravity. So why two paths are different due to the same force? Explain using the idea of central force

TL;DR Summary: A question about a game which gravity affect much of the game-play. In a space game I'm trying to arrive as fast as I can on a low atmosphere planet. There's an autopilot to get me at low orbit but that would mean having a speed of zero compared to the surface I'm over if it let...

Why on Earth does anyone, let along Roger Penrose, think gravity might be what causes the wave function to collapse? The most basic experiment in quantum physics, the double slit experiment, shows that collapse is most closely analogous to whether or not the item at issue (for example, an...

Im prototyping a machine to lower liquid from a height using a chains and sprockets. Essentially liquid will fill at top, be lowered over a distance of 4.8 metres then emptied at bottom. The liquid needs to be lowered at a slow pace due to resistance on the output shaft, I am considering...

Since the radius is "very far", I cannot find the total mechanical energy by using the gravitational potential energy formula and find the kinetic energy at impact. I can't think of any other way to find final velocity without knowing the radius.

Is the linearized gravity that describes the gravitational waves of general relativity a bimetric theory of gravity? Your adding the flat spacetime metric of minkowski spacetime to the perturbed metric, usually denoted h, to arrive at g.

Hi, mathematically in the F = GMm/r^2 equation r can be very close to infinity (or the size of the universe), but gravitational force always will be some number. But how is that in the real world? Let's say we have a perfectly empty universe but only with two sun-like stars. If they are away...

One of the leading theories of physics is that forces are mediated by virtual particles. Well, it seems as though these virtual particles can escape a black hole. Why is that?

Newton's gravity depends on the euclidean distance between two masses. Two comoving frames will have different values of length between masses so the forces will be different in two frames. Is it enough to prove that the gravity rule has to be modified?

I found a paper (https://www.researchgate.net/publication/312123871_Introducing_a_Modified_Water_Powered_Funicular_Technology_and_its_Prospective_In_Nepal) where the authors design a funicular system powered by water but with a modification from traditional systems where apparently the funicular...

My current spaceship design with several ring habitats (6 in my case) works well for worldbuilding purposes, in the sense that the reader should easily be able to tell what types of facilities can be found where on the ship. That’s because the rings distinguish themselves from each other by...

Since gravity is caused by mass deforming spacetime, is gravity actually a force or just a consequence? Are there really 4 forces in nature or just 3?

I'm new to this forum and I'm not sure if I have chosen the correct subject heading. I watched this Youtube video showing how 2 helium filled balloons sank in a vacuum chamber. The presenter used this to prove that helium would sink in a vacuum. I think he was wrong. It was the balloons that...

Summary: Trying to understand the relationship between gravity, thermodynamics and entropy, thank you. Gravity can take a diffuse cloud of gas filling a given volume of space at equilibrium density and temperature, and turn it into a burning star surrounded by empty space. Does this mean that...

I was thinking about how various objects would slide down on an inclined plane, and I just couldn't figure this problem out. So let's say I have this screw or cone on its side, on an inclined plane. If friction exists, what would the motion of the screw be as it slides down the inclined plane...

Hi I'm just a student so this: F = - mg - kv (Being kv friction) doesn't sound intuitive. Looks like both are going in the same direction... I just don't get it. But that's what my book says (Symon mechanics) and my classmates are also using "-"kv . Can someone explain me please? Shouldn't...

I am trying to understand how one derives the dilaton monopole interaction. In "Black holes and membranes in higher-dimensional theories with dilaton fields", Gibbons and Maeda mentioned that one could obtain the dilaton monopole interaction as such: where the action is given by However, I...

While solving this question I could not figure out the concept of two blocks sticking together. the question is, Two particles A and B of masses 1 kg and 2 kg respectively are projected in the directions shown in figure with speed uA =200m/s and uB =50m/s. Initially they were 90m apart. They...

I'd like to understand how gravity does not combine with quantum mechanics. At least there is no accepted theory of quantum gravity, so I assume it is not solved? I'm only starting to learn QFT and eventually GR. Maybe, someone can already outline where those theories fail to combine and comment...

I am reading a popular-science book Reality Is Not What It Seems by Carlo Rovelli, one of the founders of loop quantum gravity. He writes: and and So basically, space (spacetime) is just another quantum field like all the others, and the quanta of this field is the nod. Nods have volume...

Hello, In the Wikipedia article on "Inflaton" there appears the following formula: ##S=\int d^{4}x \sqrt{-g}[ \frac{1}{2}m^2_{P}R-\frac{1}{2}\partial^\mu\Phi\partial_{ \mu }\Phi-V(\Phi)-\frac{ 1 }{ 2}\xi R \Phi^]## with ##\xi## representing the strength of the interaction between R and...

I saw 2 recent papers on MOND are they promising [Submitted on 21 Jul 2022] Noncommutative geometry and MOND Peter K.F. Kuhfittig Comments: 5 pages, no figures Subjects...

Greetings. I registered to this forum because of a particular issue regarding Gravity. I'm no astrophysicist or mathematician, i searched to find an answer, but the terminology and equations are a little much for me. I feel the best direct way is to ask people with the right expertise. It is...

Not sure how to mark the level, I know what the math in the Einstein field equations represents (stress energy tensor, Riemann curvature etc), but have no facility in doing anything with that math. so take 2 black holes, with say 100 solar masses. A is not spinning, B is spinning at...

Hello, I noticed while trying to calculate the stardart gravity acceleration of the Earth that I never arrived at the defined value of 9.80665 m/s2 no matter that I calculate it with the equatorial radius, the polar radius, mean radius or the average of the equatorial and polar radius. With what...