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'm trying to understand potential energy, especially with regard to gravity. There's a double negative that's difficult to grasp: The direction of the force is negative because the vector points radially outward and the force of gravity is directed inward, and the work done to bring an object...
In Schutz says When we have weak gravitaional fields then the line element *ds* is
$$
ds^{2}=-(1+2\phi)dt^{2}+(1-2\phi)(dx^{2}+dy^{2}+dz^{2})
$$
so the metric is
$$
{g_{\alpha\beta}} =\eta_{\alpha\beta}+h_{\alpha\beta}= \left( \begin{array}{cccc}
-(1+2\phi) & 0 & 0 & 0\\
0 & (1-2\phi) & 0 &...
For my physics assignment we have to design and test a way to allow an egg to fall from a three storey building and not crack. The only requirments are the egg must be visible in atleast one place and the smallest design wins. I tried making a crumple area and then protecting the egg with...
If a ship could cancel out the effect of gravity, wouldn't it be able to pass through the event horizon of a black hole, and take a tour of the singularity, and then just report back with its observations?
Also, if a ship had the capability to cancel out the effect of gravity, wouldn't this...
Propose an experiment:
Simultaneous test of matter warping space (Gravity) and quantum entanglement "spooky action" at a distance where the spin of the other particle instantly changes to clock or counter clock.
Will the result be that both Symmetric Changes are instantaneous?
Or will it...
Here's what my prof says:
"Define F_{mean} to be the mean force, F_close to be the force on the side of the Earth closer to the moon, and F_far to be the force on the side of the Earth furthest away from the moon.
On the closer side the net force is F_close - F_mean > 0
On the further side the...
Some time ago I tried to define classical inverse-square gravity on a 3-dimensional (cubical) torus T3: the quotient space obtained by identifying opposite faces of a unit cube. (Or more rigorously, the quotient space
T3 = R3/Z3
of R3 by its subgroup Z3 of integer points.)
I assumed there...
Is the theory that inflatons become dominate when gravity is strong (as in right after the big band) and when gravity is weak (as in driving the current expansion of the observable universe)?
Homework Statement
A horizontal pole is made of 8 pieces, 1 meter apart each. Forces that do not act at the ends are shown in the picture.
The pole does not rotate, and weighs 20N.
a. What is the sum of forces applied on the pole?
b. Where is it applied?
c. What are the forces at the ends...
Homework Statement
I searched around and found a manual, so this time I have the complete question in English (I'll use different numbers though, because mine is the 8th edition, and the manual is from the 14th, but it's not something that affects this exercise):
2.98) An alert hiker sees a...
I just read about how professor Erik Verlinde saying that 'gravity is not a fundamental force of nature, but an emergent phenomenon. In the same way that temperature arises from the movement of microscopic particles, gravity emerges from the changes of fundamental bits of information, stored in...
Here is the arxiv link. I'd be interested to hear comments from people more expert than I. The claim is that both dark energy and dark matter can be understood as consequences of gravity as an entropic force.
Does gravity affect waves such as gamma, xray, radio etc. and how does it interact with other wave forms considering gravity is a wave itself.
Respectfully,
Pat Hagar
Homework Statement
Sputnik I was launched into orbit around Earth in 1957. It had a perigee (the closest approach to
Earth, measured from Earth's center) of 6.81 × 106 m and an apogee (the furthest point from
Earth's center) of 7.53 × 106 m. What was its speed when it was at its perigee? The...
I know that there is constant acceleration due to gravity. A regular force that is applied to a moving object causes the object to accelerate once and as long as the force is present. Meaning, if a ball that is rolling experiences a wind force of 5N the ball's movement will increase 2 mph for...
Pressure can exist in a container of gas even if there is no gravity. From kinetic theory of gases it is assumed that pressure exists due to momentum transfer between molecules and the wall. Suppose I have a closed container on Earth at sea level filled with air. Now I carried it to zero gravity...
Homework Statement
A 10kg bucket of water is lifted vertically 3.0m at a constant speed. How much work did gravity do on the bucket during this process?
Homework Equations
Work=Force*Distance (what thought to use)
Wext=Fextdcosθ (what the answer key says to use.
The Attempt at a Solution
My...
Does a static uniform E field in space appear to be a mix of E and B fields to an observer on Earth (ignoring the Earth's motion)?
My GR is not so great, but would the rigorous way to calculate the new fields be to parallel transport the Maxwell 2-form ##F_{\mu\nu}## from free space, where it...
Howdy!
So I wrote a novel a while back called Breaking Gravity (info at the bottom) and about two months ago, the book suddenly took off found a pretty big audience.
I'm now considering adding a follow up, but I'm looking for ideas. Specifically, the reason I'm here is that I'm hoping you...
Is this line of research a reality?
https://www.sciencedaily.com/releases/2016/01/160108083918.htm
Produce and detect gravitational fields at will using magnetic fields, control them for studying them, work with them to produce new technologies -- it sounds daring, but Prof. André Füzfa of...
When International Space Station is at rest, it revolves around it's axis once per orbital revolution (92.65 minutes). In other words, is tidally locked. Does the spinning around it's axis do create non-zero artificial gravity? Does it have non zero angular momentum?
Hi,
I read about definition of microgravity. It is usually described as reduced g, but not zero g. How can one say then that an object is in microgravity? I was looking hours for a clear definition, like an object is in microgravity if there are just 10^-6g left (clearly wrong, because I read...
Question:
On the Moon, the force of gravity on an object is only about one-sixth of its value on Earth. Decide whether each of the following would give an accurate measurement of the mass if used on the Moon
a) A beam balance like the one in the diagram at the top of the page
b) A balance...
Based on this website and the image that is portrayed it shows a dip in space going downward. I'm just curious as to how are these images made if there is no sense of direction in space? Shouldn't gravity be warped around the planet and not dipped downward, and if so, why are we informed with...
Homework Statement
Planet X of mass mx = 2.1 × 1024 kg orbits S in uniform circular motion at a distance rx and with a period Px = 2.1 years (=66225600 s). The mass of the star S is MS = 2 × 1031 kg and its radius is RS = 3.2 × 108m.
Homework Equations
T=2pi * sqrt(r3/(GM)
The Attempt at a...
in classical GR the strength of gravity increase to infinity as mass increases and distance decrease.
in classical GR a black hole consists of an event horizon, and a singularity of infinite density and point-size inside the black hole.
in LQG/LQC strength of gravity eventually becomes...
I see that this had been asked years ago, but I want to know if something new arise from this question.
Does quantum foam (virtual particles), with the sum of all these virtual particles popping into existence, may exert some gravity background?
If the sum of all this virtual particles popping...
<< Mentor Note -- OP correctly re-posted schoolwork question in the HH forums; threads merged >>
The full question is: The pendulum inside a grandfather clock has a half period of 1.0000s at a location where the magnitude of the local acceleration of gravity is 9.800 m/s^2. The clock carefully...
Homework Statement
You are explaining to friends why astronauts feel weightless orbiting in the space shuttle, and they respond that they thought gravity was just a lot weaker up there. Convince them and yourself that it isn't so by calculating how much weaker gravity is 250 km above the...
Hello! I am a bit confused about Kepler 3rd law for circular orbits. So assume you have 2 bodies of masses M>m orbiting in circles around their center of mass. As the center of mass passes through the line connecting them, they must have the same period. But according to Kepler's 3rd law, this...
Do falling charged particles radiate? Also, if I hold a charge still and bring a large mass close to it first on one side then another so that the particle sees a sinosoidally oscilating gravitational field will it radiate?
Consider symmetry SO(1,3)xU(1)=SU(2)xSU(2)xU(1) and puting a local spontaneous broken symmetry:
Φ→exp(iαaτa)exp(iαaτa)exp(i(β/2))Φ
The field Φ acquires vacuum expectation value: <Φ>=(0,v).
Then ΔL=½(0 v)(gCμaτa+gAμaτa+
½g'Bμ)2(0 v)T.Then we find out three massive boson,one massless photon and...
On the one hand, gravity waves travel at c, but on the other hand, spatial expansion has no speed limit; ie, it can happen at FTL speeds. At first one might think, "So what? Gravity waves are gravity waves and spatial expansion is spatial expansion." But what is a gravity wave other than the...
Hi,
I was doing an experiment with Neodymium magnets and a long copper pipe (3cm internal diameter) to see Lenz's Law in action. At first I used a long bar magnet (about 15cm long) and there was little resistance to the magnet falling through the pipe. It was only slightly slower than a...
I was thinking about writing a novel where the setting takes place on a planet with a gravity similar to Mars or even the moon (Luna). My thought was that if the atmosphere was dense enough wouldn't that act in a similar fashion to increased gravity?
According to observations and known models mass is equal to the amount of atoms in a given space, and gravity is proportional to the amount of mass in a given space (ie. Sun > Earth > Moon) If those observations are undeniable then my question remains: is gravity directly related to groupings of...
Homework Statement
Centre of gravity - the point at which:
1) gravity acts on a body or 2) weight of a body may be considered to act.
The answer is 2) and I understand why - because gravity acts all over but it is easier to calculate a single point, an average point of where the mass is...
Was surprised to read this news story from South Africa. I guess this is what happens if your science education isn't poor.
http://www.thetimes.co.uk/article/lecturers-fear-worst-as-students-add-african-science-to-demands-wncgpq5fm
I just heard something that made me realize I was taking the equivalence principle way too literally. If I were in a windowless room, and was standing on its floor, then there is, in principle, a performable experiment by which I could determine whether I was moving upward at 1 g of...
In the beginning of the universe, the hot matter of the entire universe was confined to a small volume.
I would guess that compared to our time frame, time flowed slower than it does now.
I would also guess that time has gradually slowed down since then. Is this significant in predicting the...
Can anyone link me to some maths for gravity.
After the gravitational wave discovery I was thinking about using Pi and wondered if this was already a thing.
I am not a science person, I dropped out of school but something is pulling me towards understanding the questions I have in my head but...
If say you have some scalar field, θ(x^u), where x^u represents the 4-vector coordinates of spacetime, and then the typical classical equation of motion, a = -∇θ, how would one go about 'generalizing' this to a relativistic version? Since F = ma, would you have to write it as d/dt (P^u)...
Hello,
I've been thinking about the nature of Newton's Laws and had a question about two scenarios where I'm noticing a difference in the way the problem is framed and the outcome. I cannot sleep because it is wracking my mind.
Let me start by stating what I know to be true going into the...
Loop Quantum Gravity, Exact Holographic Mapping, and Holographic Entanglement Entropy
Muxin Han, Ling-Yan Hung
(Submitted on 7 Oct 2016)
The relation between Loop Quantum Gravity (LQG) and tensor network is explored from the perspectives of bulk-boundary duality and holographic entanglement...
Four principles for quantum gravity
Lee Smolin
(Submitted on 6 Oct 2016)
Four principles are proposed to underlie the quantum theory of gravity. We show that these suffice to recover the Einstein equations. We also suggest that MOND results from a modification of the classical equivalence...
"The weight of an exercise book in picture A (where the centre of gravity is not on the axis of rotation) rotates so it moves towards the second position in picture B (where the axis of rotation goes through the centre of gravity). Explain why."
I don't believe any equations are necessary for...