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.
http://www.google.it.ao/books?id=4qp8AAAAIAAJ&pg=PA212&focus=viewport&vq=%22yet+untouched+10,000+more+were+faithfully+collected+:+some+of+which+without+question+would+render+the+text+more+beautiful,+just,%22&dq=editions:ISBN0803974612&lr=&output=html_textThe last clause of the second position I...
Here is the picture where person balancing a toy bird with using center of mass.
I am bored with center of mass. I want to try same experiment with center of gravity. Is it possible to use center of gravity to balance bird toy ?
When i get into discussions regarding "Gravity" i say that it is a force that is caused by gravity. that the acceleration is due to gravity. there are some, like George Musser who have recently said, "Gravity is not a force, but can be thought of as a force". i think what he means is that...
Hypothetically, if the universe was completely empty, and two apples were 10,000,000,000 light years apart, would their gravity be strong enough to eventually bring them together?
The typical equation for the height of a projectile on Earth after ##t ## seconds is
## h = -4.9t^{2}+vt+c##
where ##v## is the velocity of the projectile and ##c## the initial height.
This is nice and all but what happens if the height is very large? The leading coefficient of the equation...
In a recent study (https://phys.org/news/2018-08-flaw-emergent-gravity.html) it has been discovered an important flaw in Emergent/Entropic Gravity because it has been discovered that holographic screens cannot behave according to thermodynamics...
But then, doesn't this also invalidate...
Hi
I am trying to roughly calculate a force.
If i am moving an object towards the Earth and then stop it, how much force will this generate?
a=vf-vi/t
- vi =0.6m/s
-vf= 0
-t = 0.1 s
This equalling - a
Then applying f=ma
m=150kg
Im unsure how to add gravity into this.
would...
0-(9.8+0.6)/0.1...
If you have two different liquids (water and oil for example) mixed together and free floating without gravity, will they separate as they do here on Earth? If so, what property would determine the layering structure? I suspect they would separate, and if left undisturbed probably form a...
Summary: Lower than average weight at the equator causes the Earth to be wider, yet positive gravity anomalies are claimed to cause an increase in sea height.
Summary: Lower than average weight at the equator causes the Earth to be wider, yet positive gravity anomalies are claimed to cause an...
I read that just a few feet difference in height would show a different rate of time and that was measurable. However, If the clock that is at a more elevated position it will be traveling through more space, is that what is responsible for the difference in the rate of time for that clock? I...
How much is too much gravity for life as we know it to exist on a body too small to become a star? At approximately what multiple of 1g would life as we know it be impossible because of the direct effects of gravity? What about secondary factors--e.g. how the higher gravity would affect the...
Dear Physics Forums people,
My problem lies in understanding how the following line integral, which represents work done by the gravitational force, was calculated
Specifically, in the integral after the 2nd = sign, they implicitly used \hat{r}\cdot d\vec{s} = dr
I wish to understand what...
Is it possible to reduce and/or modify the EFE so that they make the exact same prediction as Newton's law of gravity? I am wondering if the slight differences in prediction from these two mathematical approaches can be identified at a particular place in the EFE or if it's the geometrical...
So using conservation of energy where v0 = 7000 m/s
$$ K_{i} + U_{i} = K_{f} + U_{f} $$
$$\frac{1}{2}mv^{2}_{0} - \frac{GMm}{R} = \frac{1}{2}mv^{2} - \frac{GMm}{r}$$
where R = the radius of the Earth and r = the distance from Earth's center plus the height its orbiting
$$v =...
Under Newton, gravity is what I term an "invisible magic rope" that pulls you down.
Enter Einstein. We do away with the invisible magic rope, and say that space (or space-time) is warped by mass.
However, we still have other forces, that (as far as I know, anyway) are "invisible magic ropes."...
Well the first one that comes to mind is gravity and maybe centrifugal/centripetal force. I imagine that forces such as drag shouldn't even be considered. I find it difficult to imagine which belong to which frame of reference.
In Special Relativity, you learn that invariant mass is computed by taking the difference between energy squared and momentum squared. (For simplicity, I'm saying c = 1).
m^2 = E^2 - \vec{p}^2
This can also be written with the Minkowski metric as:
m^2 = \eta_{\mu\nu} p^\mu p^\nu
More...
I realize that my understanding of this matter and it's vast number of related concepts is rudimentary and incomplete.
Kindly forgive my ignorance and try to explain your thoughts in layman's terms.
Thank you for your time.
I have a question I have been wondering about lately ,somewhat abstract . Hopefully my description will be adequate . Here it is … The Earth revolves around the sun because of the suns gravitational pull and Earth's inertia . It takes about 8 minutes for sunlight to reach the Earth . What would...
From the proceedings of Group32, the 32nd International Colloquium on Group Theoretical Methods in Physics (9–13 July 2018, Prague):
https://iopscience.iop.org/article/10.1088/1742-6596/1194/1/012097
M D Sheppeard
Abstract: A physical approach to a category of motives must account for the...
Hey,
This isn't a homework question I need help with but more of a concept I can't seem to grasp.
I understand that Centre of Gravity is: the point on a body where all the weight can be considered to act.
And I understand how to find this point on different types of bodies.
However, this...
If we have an object in space (deep space where it is under no other gravitational influence) and we push it a little so that it gains some velocity and after some time comes into the influence of a planet's gravitational field and crashes on it. Where is that energy from the crash coming from...
I have never felt comfortable about trying to explain gravitational attraction to children by using heavy balls running around elastic rubber sheets. After all, it is using gravity to explain gravity. It would be so much better to explain it more like it really is, thanks to that originally...
The main role in quantum gravity can be played by the uncertainty principle , where is the gravitational radius, is the radial coordinate, is the Planck length. This uncertainty principle is another form of Heisenberg's uncertainty principle between momentum and coordinate as applied to the...
Are there new hermitian operators in quantum gravity?
Background: In many worlds interpretation (MWI). We have the preferred basis problem and the basis are for example position, momentum, spin. Each of those bases come from a hermitian operator: they are the eigenbasis of the (for example)...
I'm working on a planet that is earth-sized, but has been essentially a dead stone for millions of years: no volcanic activity, the core has completely cooled down, the atmosphere has long since drifted off. In turn it has been mined for so long that a sixth of its mass has been dug up and...
Its been awhile since I even thought about conducting a scientific experiment, and I do remember that you need a dependent variable.. the observation or effect such as the apple fell from the tree, and then the independent variable, such as gravity. But in order to test the hypothesis, you...
The best story from space I remember is how NASA spent a huge pile of money trying to get a pen to work in so little to no gravity in space. They worked and worked away and the Soviets found the solution: using a pencil.
In the 1970s, Ni formulated an alternative theory of gravity (The Astrophysical Journal {\bf 176}, 769 (passage on pages 791 f); see also Misner-Thorne-Wheeler, page 1070). Though in conflict with observation, I am interested in its fundamental properties. Ni has a scalar ##\Phi## as the...
So, I have this idea for the FTL engine for artistic purposes and I wanted to ask if anybody could point out it's flaws. I would greatly appreciate if you were willing to discuss them further. It is just a rough summary, so if you want me to disclose more details, ask away.
The idea is as...
Or both?
The cycling between 'stretch' and 'squeeze' is caused by the orientation changing of the black holes with respect to us. Correct?
This is understood as waves (or pulses) moving through space, Correct? So they take time to get to us.
So, consider the orientation which yields us being...
From what I have read gravitational waves are caused by the acceleration of massive object causing ripples in space time. What specifically causes this, and how does general relativity predict these. Does it have to be a high density of matter, or a large amount of it. How do these waves affect...
Hi, I am also having problem with the assumption Entropy makes about the movement of molecules in a 3D space. Does it assume that gas molecules could have equal chance of going in any direction? If so then how is it possible outside a free-fall lab as Gravity bias would always make all the...
I posted this earlier, but the thread has been closed.
String theorists frame much of their studies in the context of Planck length. The theories are meant to fold together QM and general relativity. The equation for Planck length includes the gravitational constant, G. It seems to me the...
Based on our current understanding of astrophysics, what's the largest possible rocky planet, theoretically speaking, with a surface gravity of 1g?
The larger the planet, the lower the average density, and there's a structural lower limit to the density.
This study from Johns Hopkins University shows that even if we manage to nuke an asteroid and "destroy" it, it will have a core back, in almost 2 hours.
Nuking them was a bad idea before, but now seems worse.
More details here...
I have a strange question. It's strange because I don't need a correct answer. I need an answer that seems correct and leads to predictable results. I'm making a multiplayer computer game where the players fire cannons in outer space. The cannon shells will move through the gravitational fields...
Hello everyone!
I am an undergraduate getting three bachelors in Anthropology/Ecology/Neurosciences (just to show off of course), but sadly no true physics (I don't show off that much, I'm still humble).
I am working on a personal project, a tabletop role playing game, where my main struggle is...
Homework Statement
Consider an elliptical orbit of a satellite (of mass m)
around the Earth (of mass M >> m). The perigee is at ##r_A## and the apogee at ##r_B##, as measured
from the centre of the Earth, itself located at one of the focal points of the ellipse (see Fig. 1).
We work in an...
Square law?
i raise this question because of recently reading some QM, and realizing that for significantly short periods of time, it becomes hard to detect the mathematical patterns. E.g. in the double slit experiment, the standard pattern doesn’t appear after just a few photons. It takes...
When an object is resting on a surface such as the floor, there are exerted on it two forces: The normal force - force of the ground - and the weight (the force of gravity, the Earth pushing the object down), the forces drawn on the left.
What are the forces on the right? Are they the same as...
Hi,
How to calculate the position in time by applying a force, like a Thrust, not in the center of mass:
I only know about the linear and angular formulas: Pos/rotation = 1/2 * F * Time^2
I have struggled finding topics about this maybe because i don't know the correct nomenclatures and maths.
Hi everyone,
I have this topic ,and I searched all over the internet without any results
what is the affect of Laser Beam on cancelling the Gravity or reducing it
if anyone can refer to a reference that can help me I will appreciate it
I've been searching the web for an answer to my question without success, My question is...
Is it possible to equate the gravity weight we experience on Earth with the PSI you would experience in places as deep as the Mariana Trench at 10,994 meters which would approx. equal 16,000psi?
ex. Would...
<< Mentor Note -- thread moved from the Introductions forum to the technical forums >>
Hello there,
This is my first post, I find myself often wondering about the universe and how it works, and there are a couple of things I just can't wrap my head around.
According to wikipedia the force that...