Gravity Definition and 1000 Threads

In this paper (https://arxiv.org/abs/astro-ph/0603302) the authors derive the field equations for f(R) gravity considering a spherically symmetric and static metric. Now the Ricci scalar only depends on r so you could write f(R(r)) = g(r) for some g. However what it seems the authors have done...

Homework Statement The center of a 1.40 km diameter spherical pocket of oil is 1.40 km beneath the Earth's surface. Estimate by what percentage g directly above the pocket of oil would differ from the expected value of g for a uniform Earth? Assume the density of oil is 8.0×102kg/m3. Homework...

This is a rather old issue, but one that has recently been on my mind. We often say that gravity is the curvature of space-time, with good reason. At the same time, we also talk about the "gravity" in Einstein's elevator, as an example of the equivalence principle. This is also with good...

If, according to general relativity, gravity doesn't exist and falling bodies simply follow curved space, what starts them falling to begin with? If a car parked on a hill slips its brakes what starts it rolling downhill, and what force accelerates it?

Time is neither matter nor energy then why it is influenced by Gravity?

Homework Statement https://ibb.co/g6iKDQ Calculate the magnitude of the force on cables 1 and 2 in the figure below if θ_1 = 55° and θ_2 = 35°. (Round your answers to two decimal places.) Homework Equations Is my method incorrect or did I go wrong somewhere in my calculations?? The...

Appearently, two beams of light in a vacuum are attracted to each other. Photons have no Newtonian mass, but their relativistic mass (e=mc^2 or mass-energy equivalence) causes this (as is my understanding). So will a 10^4 Hz beam bend more towards a 10^20 Hz beam than the 10^20 Hz bends towards...

“If the weak gravity conjecture is right, loop quantum gravity is definitely wrong,” said Nima Arkani-Hamed, a professor at the Institute for Advanced Study who co-discovered the weak gravity conjecture. source...

Homework Statement [/B] http://imgur.com/a/Ssolz Homework Equations [/B] Elastic Collision so $$ mgh = \frac{1}{2}mv_i^2 = \frac{1}{2}mv_f^2 + \frac{1}{2}I\omega^2 $$ $$ F=ma $$ The Attempt at a Solution [/B] So the problem is similar to this one which allows me to work out the normal force...

hey guys! i am very confused about the concept of potential energy and gravity. we know that as an object is continuously lifted above ground, its potential energy increases. but i was wondering if that potential energy is physically affecting the body, like if the potential energy increases...

Hello, this is my first experience in this forum. :) I was wondering if someone can help me understanding my accelerometer data installed in a project consisting in an object that is dropped in the air from an altitude of approximately 1000 meters. The descent is controlled by a parachute...

Homework Statement My professor said that since gravity pushes down any object on earth, the objects themselves push up against earth. Intuitively this is difficult too grasp, can anyone give an example or anything to help me out. Thank you

So there will be a few hypothetical in the original story here, but in the end ill wrap it up with what I believe are facts. My question, how does Einstien’s theory of relativity interact with consciousness? Let’s say I have a twin, he becomes a farmer and I become an astronaut. I go to space...

Hi all, I'm doing some reading about special/general relativity, and have come across the ideas of curved space etc. I've very much a novice in physics, so please excuse my (possibly) stupid questions. For background, I'm interested in writing a sci-fi story, and would like to have at least...

##2+1##-dimensional Einstein gravity has no local degrees of freedom. This can be proved in two different ways: 1. In ##D##-dimensional spacetime, a symmetric metric tensor appears to have ##\frac{D(D+1)}{2}## degrees of freedom satisfying ##\frac{D(D+1)}{2}## apparently independent Einstein...

Why is it the case that, in a semiclassical description of the Einstein-Hilbert action, the cosmological constant is small in Planck units? Why does this mean that $$\ell \gg G$$ for ##\Lambda = - 1/\ell^{2}##?

In the rest frame , the measured time interval is the time elapsed between the two ticks (so two events T1and T2) of one clock. In moving frame,the time elapsed between the two ticks T1and T2 are measured by the two synchronized clocks kept at two different places x'1 and x'2. The...

I read paper https://arxiv.org/ftp/arxiv/papers/1011/1011.3719.pdf . I do not understand figure 2. Such double phase space (x-p) can be also for a harmonic oscillator. But, at a harmonic oscillator we cannot have two ellipses (or a circle and an ellipse) which touch on some points, but have the...

Currently reading the following document which is a bit of a brain overload at the minute! Im considering Equation (4.61). It is the general relativistic correction due to the Schwarzschild field for a near Earth satellite when the parameters \beta, \;\gamma \equiv 1. However, as you will...

In coordinates given by x^\mu = (ct,x,y,z) the line element is given (ds)^2 = g_{00} (cdt)^2 + 2g_{oi}(cdt\;dx^i) + g_{ij}dx^idx^j, where the g_{\mu\nu} are the components of the metric tensor and latin indices run from 1-3. In the first post-Newtonian approximation the space time metric is...

If we assume I live in Jupiter and there is one year passed in my clock how many years passes in the earth? And how can I use that Equation in the attached?

Einstein proved that gravity wasn't a force, but a distortion of spacetime, when he got some guy to take a photo of an eclipse in Africa. Also we have more proof today because time is slightly faster on the ISS than on earth. So when I google it, why does it say gravity is a force? Why does my...

I have looked but do not seem to be able to pin down how Hubble's Constant deals with Gravity. Is it considered as Newtonian or Einstein special theory?

I got stucked with a solution of a problem. I have a pendulum of r radius which is in G gravitational field. So the working acceleration on the bob is a function of the angle. That is Gcosθ. The mass of the bob = m The radius of the string of the pendulum = r Gravitational force is G. So the...

In analogy to the fine structure constant, the dimensionless coupling constant of gravity is defined as some reference mass divided by the Planck mass, squared. But what is the reference mass?? I have read thread...

Hi, I'm trying to figure out the equivalent change of the Centre of Gravity when an amount of liquid is reduced. This could be a fuel oil tank on a ship. In other words, if I e.g. reduce the content what would be the equivalent vertical change of Centre of Gravity on a ship with a total...

Homework Statement Homework Equations Flux rule: ξ= -dΦ/dt' F= ma The Attempt at a Solution Let's assume that the loop is going down with speed 'v <0'. Using Flux rule, ξ = - Bva Current will move in clockwise direction to increase Φ. The effect of magnetic force on AC gets canceled by the...

The speed of light (in the vacuum) is a function of the permeability and permittivity of the vacuum. In other mediums the phase velocity will be different. It is assumed (by me) that the speed of a gravitational wave does not change depending on the medium i.e. a gravitational wave would not...

In trying to understand the relationship between Higgs particles and gravitons, I would like to pose a question on hypothetical question: What would happen if you increase the Higgs field around a planet? It seems it would mean its mass increases, which would mean its gravitation increases...

Homework Statement Homework Equations Centre of gravity: X=m1x1-m2x2/m1-m2 MOI rectangle: 1/3ml^2 MOI triangle: 1/18md^2 Radius of gyration: Ixx=mk^2 The Attempt at a Solution Mass of body 1: b*l*p = 0.8*1*10=8kg Mass of body 2: 1/2b*h*p = 1/2(0.4)*0.6*10=1.2kg1.1 X=m1x1-m2x2/m1-m2...

Suitable for a student who has a background in undergrad general relativity. Many thanks

In his little book for the layman, Seven Brief Lessons on Physics author Carlo Rovelli states: What is it about SR which is incompatible with gravity-as-a-force?

Let's assume that negative mass is possible. How would it react with gravity? Since F=ma, the acceleration would be in the opposite direction to the force applied. Keep this in mind :wink: Now, the gravitational force, F=GMm/r2. Usually this force acts towards the centre of the Earth since 'G'...

I am aware that an observer in free fall in a gravitational well will measure the local speed of light as c, but what about someone outside the well. Imagine this, Me and my friend are near Earth, and he starts freefalling to the surface, while i stay in space. If he then fires a laser beam at...

We say that, for gravity, F=mg, where g≈-9.8 m/s2. Then, we have U=mgh. But, it seems like that equation would only work if g were positive 9.8 m/s2. That is, because ##F=-\frac{dU}{dr}##, and ##\frac{dU}{dr}## is essentially ##\frac{dU}{dh}##, we should get F=-mg. So, for the two equations to...

Homework Statement If the centripetal force is at the left side of the equation; that means if we move it over to the other side, it'll have a negative sign, which means it is opposite in sense in relation to N and mg. But how is that possible, considering that the centripetal force always...

Homework Statement Let g be the acceleration due to gravity at the Earth's surface and K be the rotational kinetic energy of the Earth. Suppose the Earth's radius decreases by 2%. Keeping all other quantities constant, (a) g increases by 2% and K increases by 2% (b) g increases by 4% and K...

As I understand Aristotle believed that gravity was caused by certain objects trying to find the centre of the universe which was of course at the centre of the Earth. Newton gave us a better theory of gravity, but there were heliocentric philosophers before Newton. Not just Copernicus , Galileo...

Can someone explain how gravity pushes? I know that it bends space-time, and I've seen pictures of this. But in all of the pictures, they are just objects on a flat surface. Is it really like this, because then wouldn't space-time itself have its own gravity.

It is often said that gravity is a curvature of space-time and not a force. But since gravity is caused by mass, there must be some way in which mass curves space-time. What are the equations for how mass affect space-time?

Is it possible that the reason why gravity is the weakest fundamental force is because it is disappearing into the distant future? Similar to string theory's notion that gravity dissipates into other dimensions, only in this case it is time it dissipates through? Radon 220 and radium 224 nuclei...

Hi guys. I'm new to this forum so I'm not sure if I'm posting this in the right place or correctly, but I was totally stumped on a Physics 12 question as I was studying for my exam. The question is: An explorer spacecraft is descending towards Mars using a rocket engine for braking. The...

1. The problem statement, all variables and given/known There is an Earth but the hole is not in the middle but the side.find the period of oscillation Homework Equations Simple harmonic equation.Newton gravitational force The Attempt at a Solution I got GMx/R^3+acc=0 so period of...

[Moderator's note: moved to homework forum.] Hello there, I am stuck at a problem, and I need some hits/solution strategy to get going. Suppose we consider linearized gravity, and there is some mass, ##M## at the origin at some unknown coordinates the metric is $$ ds^2 = -(1 + 2 \phi)dt^2 +...

Hey all, *this is my first post on this forum* I've read a lot about the different ways of artificial gravity on this forum, and we've discussed everything from realistic ideas that can be accomplished with today's tech, all the way to fictitious situations in sci fi books. BASICALLY, I would...

I am doing research for my aerospace engineering dissertation to plan a mission to a Jupiter trojan asteroid. I was researching the type of outgoing trajectories used in missions such as JUNO, Galileo and Europa and noticed they all use Earth as a gravity assist in getting to deep space. Surely...

Would a hollow sphere measure the same gravitationally as a solid sphere if it was the same mass? Just sharing an interesting question

Homework Statement This isn't actually a coursework problem, but I can't solve it and I'd definitely be interested in the answer! The acceleration due to gravity at the surface of a uniform, spherical asteroid is ##g_0##. Half of the asteroid is destroyed in a collision, leaving only a...

Consider the following two definitions of the surface gravity of a black hole (taken from page 23 of Thomas Hartman's lecture notes(http://www.hartmanhep.net/topics2015/) on Quantum Gravity): 1. The surface gravity is the acceleration due to gravity near the horizon (which goes to infinity)...

Hi, I have a software application which calculates the CoG of an item when it is placed on to four weighing indicators. It calculates the CoG using the weight and distance between weighing points and provides the output as an X and Y co-ordinate of the object. What I would like to do is...