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.
If we were to find some way to make the graviton self-interaction easily calculable, would applying non-perturbative renormalization on it seem any promising?
Hey guys, I reading over Taylor's Classical Mechanics book. Chapter 9, Centrifugal Acceleration Section.
In p.346 he mentions that for a free fall acceleration:
g = g_0 + Ω^2 * Rsinθ ρ
Where its radial component would be...
The current definition of Gravity is: The force of attraction between bodies as a result of their mass.
Gravity affects both the space and time of the area surrounding a mass, diminishing with distance, so is the current accepted definition truly accurate? Do I have the correct definition and if...
Homework Statement :
It takes gravity 1.43 seconds to pull a 3.67 kg cat down from a 10m tall ledge. What is the power output of gravity? [/B]
Homework Equations
P=mgd/t
P=w/t
P=power
M=mass
G=gravity
D=distance
W=work
T=time[/B]
The Attempt at a Solution
P=(3.67)(9.81)(10)/1.43
P=251.77
I have tried twice now to calculate acceleration of gravity using the general relativistic equation of geodesic deviation and both times my solution is twice the correct answer. What am I doing wrong? As an example here is one problem: Calculate the acceleration of gravity g at the earth’s...
Homework Statement
My answer seems really off and wondering if someone could just look at it before I submit answer?
Two 65 kg astronauts leave Earth in a spacecraft , sitting 2.4 m apart
How far are they from the center of the Earth when the gravitational force between them is as strong as...
What I understood is that The Schwazschild metric is obtained by setting spherical symmetry in the metric and solves the field equation in vacuum.
But is the flat metric a solution too, or does it mean that changing the coordinates induces gravity ?
I'm armchair knowledgeable about GR, but I've come up against something I can't eloquently explain (to someone who asserts otherwise and wants an unassailable answer).
What property results in time dilation even when net gravity is zero?The net gravity at the centre of the Earth is zero, but...
Thought you all might be interested in this article. It could just be hype, but there also might be something deeper to it. You hear of so many schemes of tying together quantum mechanics with a relativistic understanding of gravity, that it's easy to respond to yet another announcement like...
I am wondering why gravity needs to be unified with the other three forces into a super-force. Why can't the three forces be seen as interactions between particles in a space-time fabric whose geometry gives the impression of gravity?
This is probably a fairly simple question, but I am struggling with it. My question is: Would you experience the effects of gravity if orbiting in a stable or circular orbit close to a black hole?
This stems from my mental image of the International Space Station (ISS). There is obviously...
Greetings: I can understand that an object's trajectory curves about a greater mass (e. g., satellite in Earth's orbit). The spacetime is curved via the great mass and the moving object simply follows the curvature. My problem is this: Why does a stationary object at a short distance from...
This has been bothering me for some time, and would like to get a physicist's view of it.
If my understanding or contention is in error, please correct me (gently). I only have under grad
physics from 1970, and was a microbiologist, though am interested in quantum physics, cosmology.
My...
Warning: I'm a freshman chemistry student. My math skills are elementary at best.
Image a ball in deep space. A baseball sounds nice. Assume this ball had no initial velocity but suddenly finds itself caught in the sphere of influence of a massive body. A black hole sounds fun. The ball begins...
The equations for gravity vary differently depending on the distances involved: Inside a body, such as a planet, the weight varies directly with the distance from the center - as r. Outside of the planet or sun, gravity varies as the inverse square law - as 1/r^2. At distances at the edges of a...
Salutations, I have been trying to approach a case about projectile motion considering variation of gravity acceleration and air resistance:
A spherical baseball with mass "m" is hit with inclination angle $\theta$ and launching velocity $v_0$, then, the wind has a drag force equals to ##F=kv##...
Ok so I've asked my physics teacher and a statics teacher as well and I couldn't get a straight answer from either. So here's my questions...
Correct me if I'm wrong, but isn't the gram a unit of mass? Not weight? I thought that for mass to become a unit of weight, it has to have to...
In Einstein's thought experiment (if I understand it correctly) a person in a sealed elevator in space accelerating at 9.807 m/s2 would not be able to tell the difference between that and the effect of gravity on Earth.
Is there any sort of experiment the person in the elevator could do that...
Homework Statement
In a distant galaxy, a planet orbits its sun at a distance of m with a period of 108 s. A second planet orbits the same sun at a distance of m. What is the period of the second planet?
Select one:
a. s
b. s
c. s
d. s
e.
Homework Equations
T^2=constant * r^3
The...
To date, the most accurate verification of the time effect of gravity is where two satellites were accidentally put into elliptical orbits where the altitude varied by 8,500 kilometers ( 5,282 mi). Their atomic clocks ran slower near Earth and faster at higher altitude. The agreement with GR was...
I have read in several popular physics texts that general relativity predicts that gravity deflects light, but that Newtonian mechanics, in contrast, predicts that the trajectory of light is not affected by gravity. However, I am very skeptical and confused about this result.
We of course have...
Is there any thing like perceived gravity in circular motion??
If I consider that it is in opposite direction to centripetal force, then both perceived gravity and centripetal should cancel each other and object should move in a straight line. Why does it nit happen?
One approach that has been proposed to replicate the description of dark matter phenomena in galaxies with a gravity modification that is set forth in a simplified manner in the phenomenological toy model theory MOND is to do so through a variation on Einstein's General Relativity known as...
Hi,
It is usually claimed that a person in an accelerating elevator with an acceleration equals to the gravity of the earth; this person cannot make any experiment that makes him know whether he is in the elevator or on the surface of earth.
However, if this person project two light beams...
I would like to know if this group http://www.quantumgravityresearch.org/ and its Emergence Theory has any standing in main stream Physics.
Thanks Andrew
since it is known that ##\vec{A_\perp} = -{mG \over R^2}## why did the professor write it as ##\vec{A_\perp} = {- R G \rho \over 3}## for perfect sphere with perfect mass distribution ? Shouldn't it be ##\vec{A_\perp} = -{4 \over 3} \pi R G \rho##? I need help thanks.
Take some sort of system accelerating with respect to an inertial reference frame: let's take a spherical mass on the end of a string forming a simple pendulum with the ceiling of a car, and allow that car to accelerate uniformly.
Could someone share with me how they interpret the concept of a...
I need help with a question on my homework about circular motion. It goes like this:
- Starting from Newton's Second Law, develop an equation for the stopper that relates the force of gravity to the period.
I'm working on a story set on the moon post-industrialization. The moon has an orbital ring with a spinning exterior to simulate Earth gravity. People work on the surface in lunar grav, then go up to live on the ring under conditions more favorable for human bodies.
Two questions I need to...
Consider a spherical planet of uniform density ρ. The distance from the planet's center to its surface (i.e., the planet's radius) is R. An object is located a distance R from the center of the planet, where R < Rp. (The object is located inside of the planet.)
1) Find an expression for the...
I am still learning general relativity (GR). I know we can find the path of a test particle by solving geodesic equations. I am wondering if it is possible to derive/convert metric tensor to gravity, under weak approximation, and vice versa.
Thanks!
I have a question related to MOND and DM that I will post here rather than create a new thread. My thought stream begins with doesn't Energy create gravity as well as matter due to the E = MC^2 equation? Which leads to my question of whether or not empty space generates gravity due to the energy...
So I'm trying to help someone get an idea of the 'scale' of some of the most massive black holes, but, I'm at best a laymen when it comes to this stuff. Because ISCO for a non-rotating black hole is just 3 times it's radius, and I can calculate apparent arc radius from ISCO, I could tell them...
I just read a couple articles discussing the surface gravity of Saturn and Jupiter. I would expect the "surface" gravity of these planets to be much higher than that of Earth. I understand how the low densities of these planets has influence on that, but I thought mass was related to gravity in...
If a photon does the 4 things listed below, why do we say it doesn’t have mass? I guess I’m asking if there’s a clear definition of mass.
follows geodesics in spacetime (classically: accelerated in a grav field),
curves spacetime (classically: creates a gravitational field),
has momentum /...
Homework Statement
Block A is on top of Block B, both are of equal mass and size. Block B is being pulled by a hook at a constant velocity. There is friction between the table and block B.
Homework Equations
[/B]
What will each FBD look like? Is there friction between Block A and Block B...
My teacher say: Comparisons between the pressure of an object on the inclined plane and the gravity of the object
But idk what is sin and cos means
I need help
THANKS
from: vietnam
Hey I have a question and I’m sorry if some of you might find it too easy xD... How did people calculate or discover the gravity constant, and how do they know how much do planets weigh? Thanks for answers
They say gravity is because mass stretches space time and it makes matter fall to it and can prove it. And that makes sense when there is a lot of mass. But they say stars are made from gas clouds mostly hydrogen and helium very small atoms that start to clump together. So a star starts out a...
After I read Martin_K's post of 4:14 Oct. 30 on the frozen image of an object just before it fell through a black hole's event horizon, the next few minutes I was jumped by a handful of related ideas.
First, the frozen image scenario is illustrative because when photons are frozen in place...
We get this type of question now and then, even in the main physics forums. One such question in the Sci Fi forum is from this one:
https://www.physicsforums.com/threads/what-is-the-largest-possible-rotating-wheel-space-station.950770/
So I don't know of people have seen this video from a few...
Homework Statement
We drill a hole from the surface of the Earth to the other side through the center, drop a test particle and measure the time it takes to come back. How does this time depend on the radius and density of the Earth?
Homework EquationsThe Attempt at a Solution
The gravitation...
If gravity of the Earth is so powerful to hold the moon in orbit, why does she not drag in & squash to smitherings all on its surface?
Please forgive my ignorance, ......nick
Hello,
In the wikipedia article about solar sails the lightness number is mentioned and the calculation is the characteristic acceleration ac divided by the Sun´s local gravity (distance: 1AU): λ = ac / 5.93
why do they use 5,93 m/s^2 for the sun´s gravity and not 274 m/s^2?
So I have sort of a conceptual question about the big bang and gravity.
Imagine yourself in a universe, in which existed about the number of particles/energy in a 3X3 metre room at any given moment. This universe has the same laws of physics, constants and is identical in every way to our...
Zero gravity. We can hear about the zero gravity chamber , zero-g flights on aeroplane and lots of other stuffs about zero gravity on earth.
How does it actually works?
Can it be possible for us to make it?
Hey there,
If body 1, mass M1 has escape velocity V_e1 = (2GM1/r)**.5 but M2 is more massive than M1 is this relation still valid? In this case, the subordinate body really isn't the subordinate body so does this still hold? And r (distance b/t the two) changes not only due to the motion of M2...