Gravity Definition and 1000 Threads

Consider the following paragraph taken from page 30 of Thomas Hartman's lecture notes (http://www.hartmanhep.net/topics2015/) on Quantum Gravity: Hawking radiation is a feature of QFT in curved spacetime. It does not require that we quantize gravity - it just requires that we quantize the...

Homework Statement There is a planet (spherical) with a hollow that is concentric with the planet.if the inner radius is r and outer radius is R and mass of the planet is M what would the gravity be outside of the planet at distance x from the center ? Homework Equations Shell theorem...

Dark Matter was never found, what Modified Gravity theories should we check now?

You Heard me.:smile: Seriously, I have seen some so called low effective theories of gravity, so if they are any good why aren't they taken to be as established theories, since all other ones seem to be valid in some energy scale anyway. Although I do admit that I dislike this adding one more...

If the Earth were divided into 4 sections and separated far enough that they have no gravitational pull on each other, would the gravity on each section be 25% of the current gravity on Earth?

If the Universe is expanding, wouldn't it be common sense to think everything inside it is expanding too?

I came across this website and I intend to find out more about work done by gravity and derivation of gravitational potential energy (Sorry, the thread name is too long, so I abbreviate it as G.P.E.) Ok, here is the problem. I am quite confused with the calculation of work done against gravity...

It is recorded that someone has survived a free-fall from an airplane by being lucky enough to land on snow-laden fir trees. My challenge is this: Create a mathematical model which describes the forces at play in order to determine the viability of creating a safe and fun 'thrill-seeker'...

It occurs to me that any force which acts on all of your atoms individually (as gravity does) would have the same feature that one would not "feel" accelerated. We only detect acceleration because parts of the system are acted on by different amounts right? When we accelerate in a car, the seat...

I have a question. I have a flywheel that is 108' is diameter and it weights approximately 1600 lbs. It has an external force of 600lbs acting upon it at 90* to the axel. Like a water wheel. How can i determine the RPMs that my flywheel will turn with this type of force being applied to the...

Minimal surfaces are sort of the "shortest path" but in terms of surface shapes. So I figured I could characterize the shape of a hammock by adding the influence of gravity, much like you can get the shape of a catenary cable (y=cosh(x)). The equation of motion I get from the Lagrangian is...

Homework Statement Suppose there is an object that is a distance ##r_0## from the center of a planet that is nearby (the object is outside the surface of the planet). Let ## r ## represent the distance from the object to the planet's center. Let ## t ## represent time. The object, which is...

Homework Statement The problem is your typical N-body simulation, implemented using Python and Numpy. The implementation specifically calls for using the Euler-Cromer method. For this particular case I used the Sun and the first 4 planets of the solar system. Essentially the problem is I'm...

As we know from special theory of relativity, time flows slower for a moving observer. But also, thanks to gravity, time ticks slower and faster depending on whether the gravitational force is stronger or weaker. This f.ex. means that time will flow slower for a person living on the 10th floor...

Is it possible to compress the space without gravity?

Homework Statement Consider the same person at three locations. A: scuba diving underwater, B: standing on the beach, and C: standing on a mountain. Using <, >, =, make statements connecting the magnitude of their respective weights, i.e. ##W_A < W_B## Homework Equations Gravitational...

public class GravityCalculation { public static void main (String [] args) { double G = 6.673e-11; double M = 5.98e24; double accelGravity = 0.0; double distCenter = 0.0; distCenter = 6.38e6; /* Your solution goes here */...

Homework Statement A bullet was shot at 40m/s Elevation angle : 37° Bullet mass = 0.01 Kg Question : how much work is done by the force of gravity to the bullet since it was shot until it reaches the ground again Homework Equations mgh = E.Pot 1/2mv ^2 = E kinetic The Attempt at a Solution...

Homework Statement The Lunar Reconnaissance Orbiter (LRO) with mass m= 1850, maps the surface of the moon from an orbital altitude of 50 km. what are the magnitude and direction of the force the LRO experiences due to the moons gravity? Homework Equations Fg = (GMm)/r^2 The Attempt at a...

If the universe is expanding at an accelerating rate, either through a "pushing" or "pulling" force in a direction, and we have come from a "big bang point", then I wonder if we could calculate all our vectors at anyone moment and time to find the universal acceleration point and direction. If...

How do we know that the stars we see, or some of them are not the light from our own system falling back, and that we may be looking at light from our own star/solar system/ galaxy that has taken millions of years to fall back on its point of origin?

I saw some of these videos showing feather and some balls falling with the same speed in vacuum. But on normal atmospheric pressure they fall depending on their weight. This is just blowing my mind, WHY is this ? Does this prove Newtons Law of Gravity is wrong ? Then how is Einstein's...

I'm an international student currently at the end of my penultimate year in Msci Theoretical Physics in UK and am considering applying to US graduate programs that do high energy gravitational theories, in particular black hole thermodynamics. Both UCSB and UMD seem to be good choices...

Harvard University has an interesting article on a rod whose end that falls faster than gravity around a pivot. http://sciencedemonstrations.fas.harvard.edu/presentations/falling-faster-g How did they derive this formula? Where R is length of rod/2, or the centre of mass. Why did they use...

I was thinking through a thought experiment which led me to conclude that mass is relative. My thought process was basically this; there are two objects moving past each other. In the reference frame of either object, they are at rest and the other object is moving. Since the other object is...

Hi all, I recently flipped through a paper which got some press several years back, entitled "A Scenario for Strong Gravity in Particle Physics: An alternative mechanism for black holes to appear at accelerator experiments." There are a lot of speculative elements in the work, but the thing...

I've mention that the asteroid belt, if consolidated, would create a planet with about 4 Earth masses. I went to http://sciencing.com/relationship-gravity-mass-planets-stars-8487902.html and still don't get what I'm wondering. Would a planet with four Earth mass have a gravity four times that...

The title said it, how do you know the size or maximum area of a planet's gravity field can cover. The reason i asked this question because from the gravity equation the r is the radius from Mplanet and Mobject. So, that doesn't explain how big is the gravity field. Is it when the gravity force...

Homework Statement The space shuttle is in a 300 km-high circular orbit. It needs to reach a 520 km - high circular orbit to catch the Hubble Space Telescope for repairs. The shuttle's mass is 6.5 E4 kg. Mass of the Earth = 5.98 E24 kg. Radius of Earth = 6.37 E6 m. How much energy is required...

Note: I didn't really know where to put this. It isn't a specific problem, but I've been asked by my physics teacher, who decided to give me and a few others an individual physics course of sorts, to find the means of solving similar problems. It's the first problem he assigned us, since we're...

Homework Statement A satellite orbits the Earth in a geosynchronous orbit around the equator, meaning that its period is 24 hours and it stays above the same location on Earth at all times. (G = 6.67 x 10⁻¹¹ Nm²/kg².) What is the radius of its orbit? Homework Equations GM/r2 = v2/r = w2r...

Years ago I read an article illustrating the vastly different strengths of the electromagnetic and gravitational forces. The article gave a figure for the number of excess electrons dispersed throughout the Earth that it would require to overcome the gravitational binding of Earth's matter and...

Can it be said that time is directly related to movement? That is to say, on a quantum level, if all motion were to cease, would that not bring about the cessation of time?

Black hole or more correctly the event horizon will not let anything past through it, from inside to outside, ok. But then we get to a particle with zero mass eg. photon. How can gravity act on that particle, surely for gravity to act there must be mass? Or does it act on the electromagnetic...

[Mentor's note: moved frpm a different thread] I need to know something quick and don't want a new thread. The number one goal of quantum gravity is uniting them in a region where both occur (like in singularities). Another goal is quantum spacetime. I'd like to know if quantum gravity would...

Hi I will write physics terms but actually this is a math problem. Consider a particle which moves in accordance with the following equation $$m\boldsymbol{\ddot r}=\boldsymbol B\times\dot{\boldsymbol r}-\frac{\gamma}{r^3}\boldsymbol r,\quad r=|\boldsymbol r|\qquad (*)$$ and...

How do I calculate the gravitational mass of a cylinder of compressed gas, including the effects of pressure? By gravitational mass, I mean what I would measure on an ideal mass balance. (I know that the pressure is negligibly small in a realistic container, but I want to have a conceptual...

Hi Fellas could someone kindly check my solution, please. Homework Statement Calculate the force of gravity between you and your computer monitor. Estimate suitable values. (Women: 40 kg to 60 kg, men: 50 kg to 80 kg). Why have you not noticed this force? Homework Equations Fg =...

Homework Statement The first image: Without information on the interior construction of the boat or the mass distribution of the exterior shell of the boat, which of the following points can be the boat's center of gravity? The second image: Our boat from the previous question is now...

Specifically, what I am wondering is gravity considered to be a physical contraction of space? For instance the space between any two points A and B shrinks as gravity grows stronger. Is this the right concept?

I recently put together a simple 2D gravity simulator and I'd like to get some feedback or suggestions you may have for future updates. I'm planning to make a 3D version and improve the animation (framerate, realism, etc). This first simulation includes the Sun, Mercury, Venus, Earth, and Mars...

This came up in a discussion in another forum - the context was the gravity of a photon... for which we need quantum gravity. But imagining a pulse of monochromatic light, it was asserted that it's gravity could be well approximated by replacing one of the mass terms in Newton's Law by E/c^2. I...

Hi, I wonder if a gravitationally bound system ...like a binary star system (or a spinning galaxy for that matter) has a similar inertia in its rotational axis like your classic spinning top? Is there resistance to a change in the axis? I appreciate the system is not solid and so not obviously...

Homework Statement we did a quiz in my dynamics class, it was very easy i think but there was a problem where we had to find the speed of an object attached to a spring, but that is not my question. The mass had 8 pounds, and the spring constant was in inches, the measurements in inches. To...

First I don't have extensive knowledge about gravity beyond General Relativity, so please forgive my ignorance about this subject. I have confusion about the relation between GR and QM and I just want a general picture so that I can connect the dots. My questions: 1- Why do we need quantum...

In another forum, the question was raised, "could a ship with 1G acceleration escape the gravity well of a planet with 1G gravity?" A popular response is, if the craft is aerodynamic, it could accelerate laterally until it reached escape velocity and then manage to get to space. I don't...

If gravity was not geometry.. what conservation law(s) would be broken? For example.. if gravity was a force.. would other laws of physics be broken? But gravity as geometry may not be complete answer because it has to be made compatible with quantum. Its quite puzzling.

As gravity increases time slows, hypothetically if you were at a point with extremely low gravity would time run any faster?

Hello everyone, Last night I was reading about gravity and I come across one debate. I tried to search about it but got confused. I hope some one can help me. The question is: Why is it so hard to realistically simulate the collisions of particles, gravity all the forces that go on around...

When we finally solved for quantum gravity. Would it only give us a solution to understanding the interaction in Planck scale quantum and spacetime or would it also give us new technology?