Gravitation Definition and 918 Threads

It is well-known that Newtonian's law of gravitation \Phi(\vec{r}) = -\frac{Gm}{|\vec{r} - \vec{a}|} for the gravitational potential ##\Phi## generated by a mass ##m## located at ##\vec{a}## is in several ways inconsistent with special relativity. What one could do is to modify the...

Hi, while I'm going deeper in my SR/GR knowledge, having LQG unrderstanding as main goal ( my QM background and maths is a bit stronger than GR's one, til now ) I came across some interesting youtube lectures about Gauge theory of Gravitation...

In classical electromagnetism, Coulomb's constant is derived from Gauss's law. The result is: ke = 1/4πε = μc^2/4π = 8987551787.3681764 N·m2/C2 Where ε is the electric permittivity of free space, μ is the magnetic permeability of free space, c is the speed of light in a vaccuum, and 4π is...

Homework Statement Homework Equations ∑F=ma The Attempt at a Solution This is a problem that can be solved by looking at impulse and momentum and I understand how the problem is solved in the book but I'm wondering about the reasoning before, if this is the only way to look at it...

Hi, I've just started Gravitation and Inertia by Wheeler and Ciufolini. This is really a sort of trasure to me, since I was looking for something about it since when I read Einstein's relativity papers, involving Mach's principle. The main point is really simple "Inertia here arises from mass...

Homework Statement A uniform sphere has mass M and radius r. A spherical cavity (no mass) of radius r/2 is then carved within this sphere (the cavity's surface passes through the sphere's center and just touches the sphere's outer surface). The centers of the original sphere and the cavity...

Homework Statement Two identical point masses, each of mass M, always remain separated by a distance of 2R. A third mass m, is then placed a distance x along the perpendicular bisector of the original two masses. (Picture attached.) Show that the gravitational force on the third mass is...

Homework Statement I'm having trouble with this problem attached. Any help would be appreciated. Homework Equations The Attempt at a Solution

Hi all, I'm currently a student teacher. Next week I'm going to teach a lesson on universal gravitation to grade 11 students. It's the first lesson on the topic, so it will be an introduction and not too in-depth. I'm struggling with ways to make it interesting. I decided to start the lesson...

Homework Statement its 3.8 x 10^8 from Earth's core to the lunar's core calculate the gravitational attraction exerted by Earth on the moon Homework Equations ag = GM/ r^2 G= 6.67 x 10^-11 M of earth= 5.98 x 10^24 ... r= 6.37 x 10^6 M of moon= 7.36 x 10^22 ... r= 1.74 X...

Homework Statement The gravitational attraction due to a nearby mountain range might be expected to cause a plumb bob to hang at an angle slightly different from the vertical. If a mountain range could be represented by an infinite half-cylinder of radius a and density ρ lying on a flat plane...

Homework Statement Let's suppose that we wanted to launch a spacecraft of mass m out of the Solar System. a) If we want to launch the spacecraft directly from Earth, what boost Δv would be required and what direction relative to the Earth's velocity about the Sun would this boost be...

page 71 he appears to define the affine connection in terms of derivatives on the locally inertial coordinates with respect to the laboratory coordinates and then the very next page claims that all you need is the affine connection and metric tensor to determine the locally inertial...

Homework Statement In the not-too-distant future astronauts will travel to Mars to carry out scientific explorations. As part of their mission, it is likely that a "geosynchronous" satelite will be placed above a given point on the Martian equator to facilitate communcations. At what altitude...

Homework Statement Particle A having mass mA is placed at a fixed distance r from particle B which has twice the mass of particle A. Which of the following statements will be true? Select one: a. The magnitude of the force on A will be twice the magnitude of the force on B. b. The...

Homework Statement At a certain instant, the earth, the moon, and a stationary 1030kg spacecraft lie at the vertices of an equilateral triangle whose sides are 3.84×10^5km in length. Find the magnitude of the net gravitational force exerted on the spacecraft by the Earth and moon.Homework...

Homework Statement Having problems on the method of calculating the acceleration due to gravity of the planet. A certain planet has a diameter of 1715 km and a density of 5254 kg/m³. The planet has a moon that orbits every 4.46 earth-days. What is the acceleration due to gravity...

Homework Statement Hello, I need somebody to double check and confirm my answer. I have absolutely no idea what the solution manual is doing. Moon effect. Some people believe that the Moon controls their activities. If the Moon moves from being directly on the opposite side of Earth...

Hello, physicsforums. I'm trying to write a proof for a function involving Newton's law of gravitation, and I seem to be stuck. The function I'm trying to build is a function of time with respect to distance. This is the formula I want to transform. \mathrm{A}=-\frac{GM}{x^{2}} For...

Hi, Homework Statement A satellite with mass m orbits a planet of mass M in a circular path with radius r and velocity v. Due to some internal technical failure, the satellite breaks into two, similar parts with mass m/2 each. In the satellite's frame of reference, it appears the two parts...

Homework Statement Has anyone solved the part (d) of 5.6 problem of that book? I am unable to solve it. It asks the reader to prove that the radius ##R## of a rotating cylinder (rotating around its symmetry axis) has to be greater or equal than ##\frac{|S|}{ M } ##, in other words...

Imagine you are in an elevator accelerating downwards with acceleration g, holding a balloon (which would fly upwards if left outside). Now if the thread you are holding snaps, what will happen to the balloon? Since the acceleration felt inside the elevator is 0, the balloon should not...

I don't get the difference between these equations: U = \dfrac{-Gm_1m_2}{r} F_g = \dfrac{-Gm_1m_2}{r^2} g = \dfrac{F_g}{m} = \dfrac{GM}{r^2} Also, why are the first two negative? Here's my thinking: The first equation is like U=mgh. Except it's when two masses are very far apart. It...

I am very interested to know which peer-reviewed journals are considered seriously by mainstream scientists for articles on SR/GR (even if they are not restricted to SR/GR only). There are a lot of 'peer-reviewed' journals out there which publish on SR/GR, but which are the well regarded ones...

Hello, I'm new here :) I'm stuck on a homework problem, even though it's probably really easy and I'm just being stupid. Homework Statement In outer space, two solid spheres of radius 10.0 cm are held 30.0 cm apart center to center. One has a mass of 20.0 kg while the other has a mass of...

Homework Statement The radius of the Earth is 6400km. A 7200n spacecraft travels away from the earth. what would be the weight of the spacecraft at the following distances from the Earths surface: 6400km, 12800km Homework Equations Fg=mg F=Gm1m2/r^2 The Attempt at a Solution Just...

I was writing a script to help me calculate gravitation and various other things when i noticed i don't know how to calculate this I need to calculate the kinetic energy of an object being pulled towards a second object until they meet knowing only the weight of the objects, the distance of the...

Homework Statement This question is from the Nelson Grade 12 Physics textbook. The force of attraction between masses m1 and m2 is 26N in magnitude. What will the magnitude of the force become if m2 is tripled, and the distance between m2 and m1 is halved? Homework Equations...

Originally I asked on another thread whether the GR effects on light can be described as light passing through a medium of varying density- so exerting its effects by refraction. A.T. kindly posted the following links: http://www.newscientist.com/article/dn24289#.UlsOR-B3Zmh...

Homework Statement Homework Equations The Attempt at a Solution I really don't know how to start with this problem. The four point masses of mass m oscillate together so I am confused as to how should I begin making the equations. Just a guess, should I write down the expression for potential...

Universal Gravitation Constant - HELP! Hello, I'm a little confused... What is the difference between the "Constant of Universal Gravitation" and the "Gravitational Force"? I know that there is a radius between two or more objects like the Earth and the Moon and bla bla bla... But the thing...

Homework Statement A star of mass 5 × 10e30 kg is located at ‹ 7 × 10e12, 3 × 10e12, 0 › m. A planet of mass 4 × 10e24 kg is located at ‹ 5 × 10e12, 5 × 10e12, 0 › m and is moving with a velocity of ‹ 0.6 × 10e4, 1.4 × 10e4, 0 › m/s. A. During a time interval of 1x10e6 seconds, what is the...

"scalar gravity" -Feynman lectures on gravitation Hi all, I'm trying to understand the following claim from Feynman's lectures on gravitation, section 3.1 (p.30 in my edition). He's considering how heating or cooling two clouds of gas would change their mutual gravitational attraction. I...

Homework Statement Two asteroids are traveling side by side, touching each other. They are both spherical and are made of pure iron. What must their diameters be in feet to exert a force of 3 lb's onto each other?Homework Equations V = 4/3*∏*r^3 density of Iron = 7.63*10^3 1 lb = 4.448N 1 foot...

Hello, Does anyone know what "induced gravity" is and where can one read (something not too technical) about it? I am trying to understand how a system with zero Lagrangian has something to do with gravity. Could someone explain perhaps? Thanks

I don't know how famous are Iranian physicists,but anyway.Once I was watching one of the videos of the Reza Mansouri's lectures on GR,it was the first or the second lecture in the series I guess and so he was just talking about general aspects of Gravitation.When he was explaining about the...

##F = G \frac{ m_{1} m_{2}}{ r^{2} } ## Where does the formula come from? And why does it work that way? How would it relate to Newton's Second Law? ##F = ma## Using Newton's Second Law, is it possible to get the Law of Universal Gravitation?

I am trying to study the motion of a falling body in the earth’s gravitational field however not assuming a constant acceleration. I want to work out the distance traveled in a given time. We know that  a = \frac{{GM}}{{{r^2}}} Likewise, we can calculate that \begin{array}{l}...

Homework Statement A planet of mass ##M## moves around the Sun along an ellipse so that its minimum distance from the Sun is equal to ##r## and the maximum distance is ##R##. Making use of Kepler's laws, find its period of revolution. (Ans: ##\pi \sqrt{(r+R)^3/(2GM)}##) Homework...

Homework Statement The electric field, E, a distance D away from a charged particle is directly proportional to the size of the charge Q, and inversely proportional to the square of the distance D. If the charge is increased by 40% and the distance is increased by 30%, by what percentage does...

Gravitation is described on one hand as curvature of space in the presence of matter. It is also described as a field acting through gravitons on matter. How can the two views be reconciled?

Hello I studied about the Newton law of Gravitation which states that in universe every matter attract each other with a force which is denoted by F= Gm1m2/r^2. But in my view it is only happen within the region of gravity of a matter. but not in the space. please can anybody help me in...

Consider a man standing inside lift which is free from all external influences (gravitational or otherwise). Suddenly someone begins to pull the lift with some acceleration. Now if the man releases a ball he sees it falls onto the floor. Since he sees the lift at rest he concludes that there is...

The law of gravitation states force between two point masses m and M is proportional to their product and inversely proportional to the square of distance between them. So I'm just curious to know how did Newton discover this law? What kind of experiments he did to derive this formula? I want...

Homework Statement So a 1kg mass and a 2kg mass are placed 10m away from each other, somewhere in between them the force of gravity cancles out. Where would am object with a mass of m be placed so that it is not affected by either of the 1kg and 2kg masses? Homework Equations Not...

"Planet X" Gravitation Question Homework Statement Planet X is a planet that has two spherical moons in circular orbits. The table summarizes the hypothetical data about the moons. Both moons have low axial spin rates. (G=6.67*10-11 Nm2/kg2). Moon A: Mass=4.0*1020 kg. Radius - Data not...

Hi guys, I'm not sure if I'm going about this the correct way, but it seems to be the only one that makes sense right now. The problem reads: Io, a satellite of Jupiter, has an orbital period of 1.77 days and an orbital radius of 4.22E5 km. From these data, determine the mass of Jupiter...

A pulsar – a highly magnetized, rotating neutron star – has a radius of 9.98 Km, a mass of 1.98 × 1030 kg, and revolves around itself at a rate of 30.02 times per second. Calculate the nearest distance that a person 1.99 m tall could approach the pulsar without being pulled and torn apart...

Homework Statement The picture attached shows the answer to a sample problem... I don't understand the last step... how does ∇g = C (1/r^2)∂/∂r(r^4) ? where did the r^4 come from and what does the triple dot triangle: "∴" mean? I understand every step except for the last one... thanks...

So for a point mass in an enclosed shell, the net force of gravity is zero (similar to electricity in a Faraday cage I presume). However, what happens when that point mass is placed in side the ring of mass m and uniform density. Say the outer shell has radius r and inner shell has radius x, so...