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.
I had a bit of a brainwave regarding artificial gravity (outside of rotation or linear acceleration). As we know "gravity plating" is just a plot device to allow sci-fi films and shows to escape the pain of having to accurately recreate a zero-g environment. But then I thought: gravity is a...
It's one of those staples of sci-fi. Unless you're going for a hard sci-fi that uses rotation or linear acceleration to achieve simulated gravity, your starship will likely use "gravity plating". As we all know, gravity plating is just a plot device, usually for shows with more limited budgets...
Could I please ask for help with the following:
Given: The centre of gravity of a uniform solid right circular cone of vertical height h and base radius a is at a distance 3h/4 from the vertex of the cone.
Such a cone is joined to a uniform solid right circular cylinder of the same material...
With a pure die, all odds are equal. With a pure die, the center of gravity is exactly in the middle of the die. But what if the center of gravity is not in the center? How are the odds then. For example, how do the odds become if the center of gravity is exactly on the line that runs through...
Hi all,
I've recently become transfixed with the idea of magnetism and gravity.
I have two main questions I'd like to see discussed more.
1. Would it be possible to harness magnetic fields for energy on earth/for acceleration between planets?
1a. Has this been studied at all?
2. Why do we...
So far, I have found g of the foreign planet, Vf of the ball, and realize that GPEiA = KEfA (Am I right here?). Thus, since GPEiA = GPEiE, GPEiE also equals KEfE. I also understand that, since the same impulse is applied to catch the objects, both objects have the same momentum at the moment...
My name is Dilip (James) I am fascinated by physics and have written three books on the subject, which indicates my level of interest.. My latest book “The Electromagnetic Universe: A New Physics” is available on Amazon and describes in detail: a new theory on the propagation of light, a new...
I want to derive an acceleration in the case for a stationary mass in the gravity field.
I found the total energy in the GR is provided by a simple equation:
https://en.wikipedia.org/wiki/Schwarzschild_geodesics
## E = mc^2\sqrt{1 - rs/r} * \gamma ##
So, this is easy to provide acceleration...
Could I please ask for help with the following question. Part 2 is my problem. I have no idea how to begin, any hints would be much appreciated:
1) Prove that the center of gravity of a uniform triangular lamina is the same as that of three equal particles placed at the vertices of the lamina...
At 0:51 in this simulation video there seems to be a brief moment upon merging that these singularities produce what appears to be negative gravitational "Spike?" that seems to bulge spacetime in an opposite metric compared to normal spacetime flatness. Is this a quirk of the simulation or is...
A recurring topic in particle physics, is the possibility of a "desert" above the electroweak scale: no new physics (new particles, new forces) until the grand unification scale or the Planck scale. It's important to remember that the Higgs boson mass was correctly predicted three years in...
I'm re-watching Star Trek TNG and I just started the episode where they encounter Scotty aboard a ship that's crashed into a Dyson sphere.
That got me thinking. What would the mass and external surface gravity of a Dyson Sphere be? I've done the math myself, but I'd appreciate someone double...
Could I please ask for help with the following:
A lamina ABCD is in the form of a trapezium in which DC is parallel to AB, AB = 2a, CD = a and AD = h and the angle BAD is 90 degrees. Find the position of the centre of gravity of the lamina from the edges AD and AB.
The lamina is placed...
[Mentor Note: thread split off from a different thread]
https://www.physicsforums.com/threads/heavier-objects-fall-faster.1002022/
Since seeing this thread yesterday, I have been trying to derive the time equation for the collision of two masses due to Newtonian gravity. Unfortunately, this...
Newton thought of gravity as action at a distance. Einstein showed that gravity is the curvature of space-time. Einstein's General Relativity is the best answer, but neither discusses gravity at the quantum level. I tend to think of gravitational force to be the result of matter interacting with...
I remember being told that heavier things fall at the same rate as lighter things when everything else is equal. But this guy does a demonstration of a Xenon balloon falling faster than a Neon balloon. Why? Also an overloaded plane may not be able to fly, but it has the same aero dynamics, it...
Could I please ask for help as to why I disagree with a book answer on the following question:
Answer given is book is $$\frac{1}{2}(a+b)$$
Here's my proposed method:
Prior to this question there is an example of a similar question:
And here is the answer:
So, to solve my question I...
Does intervening mass between two stars decrease the gravitational attraction between these two stars?
Is gravity a local phenomenon in that local mass interacts with the surrounding gravitational field caused by the local star and distant stars?
Conceptually I have never really understood Ohm's law, other than using it in calculations. My brain just cannot understand why this equation works.
I was wondering if there is some sort of gravity equivalent to perhaps conceptualise it a bit better.
Voltage: would be the acceleration due to...
I would like to understand if matter accumulates into the gravity well of the Earth?
After so many years of circling the sun I have this imagination of tritium, nitrogen, and ozone accumulating underneath the Earth into it's traditional orbit, and accumulating over time.
Is this possible and...
I'm reading through Stephen Hawking's 'A Brief History of Time' and came across this sentence in the second chapter:
" If the law were that the gravitational attraction of a star went down faster or increased more rapidly with distance, the orbits of the planets would not be elliptical, they...
Hi everybody
I saw quite a nice Youtube vid about general relativity and how gravity bends spacetime and therefor redirects angular momentum into the center of gravity. I thought the first time I begun to understand the concept but immediatly the questions poped up.
The video basically says...
Assuming that the dark matter problem is finally solved by some kind of MOND, how that would change the scene for quantum gravity?, how that would change the proposed/expected properties of the Graviton (massless spin 2 particle)?
This video explains gravity in a way I haven't encountered before (regardless of how irritating the presenter may be). Nevertheless, I find it hard to believe that a squirrel falls from a tree to the ground due to gravitational time dilation between its head and its feet. The amount is so...
Hi, I’ve got a question.
it seems that engineers, structural mainly, don’t seem to understand how gravity works regarding an endless stationary (steel) ring/bridge around the equator.
Many if not all have said that such a ring would be modeled as two half circles pushing into each other. So the...
Space exploration plays an important role in expanding our human civilisation beyond earth. But the major challenge is our difficulty of working in zero gravity. So the only possible explanation I could think of is creating artificial gravity. How can this be done ?
Imagine I hang a mass from the ceiling of a building using a rope.
The mass is hanging 2m above the floor.
Also tied "in line" with this rope, and between the weight and the ceiling, is a scale that measures the weight of the mass.
Let's say the scale reads 10 Newtons.
Now, between the...
I want know is there any unified and consistent theory between general relativity and electromagnetism ? If yes could you provide me any textbook ? I'm interest
I am currently doing my masters in theoretical physics and I would like for my phd to be something quantum gravity oriented. However it seems hard to find what's "hot" in the field those past few years and I only know the basics of these topics (though I believe this can be improved). What are...
Imagine you are in the universe of the Expanse book. First of all, you want to speed up your spaceship to reach the alien gate. And you will use Jupiter's gravity. But there is a queue of spaceship wanting to go to the gate, and they all use Jupiter's gravity to accelerate. Suddenly Jupiter...
first I tried to use gravitational force to solve it but because of the incline the gravitational force is zero. so I used normal force to solve.
Normal force is 39.36,
then f*d*cos(theta)
39.36*3.6*cos(55)
it would be cos 55 because the angle is in the direction of normal force from the...
I understand that gravity causes a neutron star larger than about 10 solar masses to collapse into a black hole.
I also understand that gravity is the weakest of the four forces.
So I find this counterintuitive and I'm puzzled that why is it gravity that causes the collapse and NOT the strong...
This is a basic conundrum that has bothered me for years:
if you or a species like you is "adapted" to Twice Gravity (or any other multiple of 9.8m/2 squared) and your life functions and capacities are near identical,
How strong/fast are you? Compared to 1G?
See, this is the issue of mass vs...
If we just prove (https://www.physicsforums.com/threads/does-every-object-rotate-around-its-center-of-gravity.998359/) that object don't rotate about CG ,why then center of gravity must be ahead of center of pressure ,for yaw stability?
Can you explain physics behind this phenomen?
Hello. What are the problems specifically or mathematically or physically that physicists find difficulty in solving to make a theory of quantum gravity? Thank you.
I passed O level Physics in 1983 and loved it but went down the arts route. Over the last 5 years or so I re-kindled my interest and have been reading a lot e.g. Hawkings, Al Khalili, Rovelli etc. I am still struggling with various things that relativity throws up.
For example I understand...
I can see how spinfoams and spin networks can describe the structure of space and time. But i have not seen what is added so that there is gravity. is it a less action principle?u
Regarding the equivalence principle of GTR, inertial mass and heavy mass are comparable, and are causing identically effects on mass objects.
The pseudo force of inertial mass could be experienced in an accelerated frame of reference. In that point the "Force" appers, while energy is...
Disclaimer - I am not an expert by any means so this might be as much about confirming my understanding as an inquiry from the general public... as such, it might be fairly conversational as I attempt to clearly communicate my thoughts and understanding. Please excuse this.
If gravity is the...
Hello everyone, happy holidays!
Y/day i googled that question (see title), and i found no clear answer, and I was really suprised,
So I had to investigate my self, this is a super basic question,
Let me know if i got this right:
Earth R: 6,371 km
Moon R: 1,737.1 km
d1: 384,400 km (center to...
Hello there. What will physicists do after a theory of quantum gravity is found?Will they ask, if it is found ,more questions about it and try to develop it?What other questions will they make probably?Thank you.
I know the solution for the problem of the tension on a rotating ring without gravity (tha is, ##\frac{mR\omega^2}{2\pi}##) - that I find simple enough. But I'm at a loss how can I change it to do with gravity :/
Any help is appreciated! (and apologies for the bad drawing)
Physics is not my area of expertise.
That being said, philosophy of science is, but I'm not here to discuss philosophy.
I recently found myself trying to imagine how light behaves once it crosses the event horizon of a black hole.
Presumably, between the event horizon and the singularity...
If singularities don't exist in QG then what prevents particles from just collapsing falling further until they collapse into a singularity? Is there a repulsive force in QG ? Is time infinitely stretched near a singularities? What else could be happening?
So what I did was find each of the forces the masses had on m1 using the above equation.
From m2 I found 19.975 in the negative i hat and for m4 i found 29.96 in the positive k hat direction using the above equation.
For m3 I used pythagorean theorem to calculate r, which was 3.25 (so r^2 was...
Hi everyone! I don't know how to solve the next problem, and if anyone could explain to me step by step how it is solved I would thank you a lot. I know it's not hard, but I'm not seeing how to do it. Thank you in advance!