Gravity is an attractive force that affects and is effected by all mass and - in general relativity - energy, pressure and stress. Prefer newtonian-gravity or general-relativity if sensible.
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4answers
294 views
Why do bullets in a magazine go up instead of down? [closed]
I've been curious about this, and it might not belong here, but I'll ask anyways.
For most modern weaponry that I've seen or used, it appears that the magazine is always placed below the barrel of ...
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0answers
46 views
Water Stream from a Horizontal Surface
If water was projected from a flat surface where gravity was equal all over the surface. What would happen when the water fell in on itself? The water is in a continuous stream and is perfectly ...
3
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3answers
118 views
Relation between the determinants of metric tensors
Recently I have started to study the classical theory of gravity. In Landau, Classical Theory of Field, paragraph 84 ("Distances and time intervals") , it is written
We also state that the ...
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1answer
104 views
Do all black holes spin in the same direction?
My question is as stated above, do all black holes spin the same direction?
To my knowledge, the spin in the direction of the spin of the matter that created them. Another similar question was asked ...
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0answers
15 views
How much time does it take to affect? [duplicate]
We know gravitational is continuously acting on us. But let us assume that we are hanging in the space alone away from anything to affect our position. And suddenly a giant planet appear's a few ...
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3answers
216 views
Gravitational Potential of a Sphere vs Gravitational Binding Energy of a Sphere
My question is about two equations regarding uniform spheres that I've run into:
$V=\frac{GM}{r}$
... and ...
$U = \frac{3}{5}\frac{GM^2}{r^2}$
$V$ is unknown to me, and is described (in Solved ...
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3answers
262 views
Speed of the Moon
Why the motion of the Moon looks very slow in the sky? Doesn't it need the high speed in order to escape the earth's gravity?
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1answer
176 views
Is the quantization of gravity necessary for a quantum theory of gravity? Part II
(At the suggestion of the user markovchain, I have decided to take a very large edit/addition to the original question, and ask it as a separate question altogether.)
Here it is:
I have since ...
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1answer
61 views
Do all forces act in the same way where gravity is close to zero?
Suppose that I put in the outer space (where gravity from other bodies is negligible) a large, perfectly round sphere totally filled with water. At the bottom (even though "bottom" doesn't make much ...
2
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2answers
55 views
Re: recoil (bounce) of objects under varying gravitational forces
First, I don't have a strong knowledge of physics, so please forgive my lack of precision in defining my question.
Consider an airless free-fall situation where a steel ball and a balsa ball (with ...
1
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1answer
102 views
At what launch angle will a (model) rocket keep flying straight?
When a model rocket is launched straight up with an angle of 90degrees to the ground it will do a 180 flip when it reaches the apex of its flight and then dive straight down to Earth.
If I were to ...
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3answers
260 views
Similarity between the Coulomb force and Newton's gravitational force
Coulomb force and gravitational force has the same governing equation. So they should be same in nature. A moving electric charge creates magnetic field, so a moving mass should create some force ...
3
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3answers
180 views
Can a black hole collapse in itself?
As we know that the black hole is a lump of highly dense matter, and that's the reason for it's so strong gravitational force. Bat let us assume that it has sucked up a huge amount of mass and it's ...
2
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1answer
96 views
What are we all falling towards?
One meteorite fell on the ground in Russia, last week. In different circumstances, it could have orbited the earth, or perhaps pass close to the earth and then disappear into the space.
It seems that ...
1
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1answer
99 views
Is light affect by gravity? Why?
I would like to know if light is affected by gravity, also, I would like to know what is the more correct for the definition of gravity: A force that attracts bodies with mass or force that attracts ...
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1answer
103 views
Does gravitational force attract bodies with mass or with energy?
On my textbook is written that gravitational force is the force that attracts bodies with mass. But I've seen on a book that It actually attracts bodies with energy. I'm having a class tomorrow and I ...
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1answer
73 views
Gravity's limits
Suppose there are only two hydrogen atoms in the entire universe. Suppose further that they are both situated at the very limits of the cosmos, equally distant. Would they exert an attractive force on ...
1
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0answers
131 views
Gravity Question Can this be reopened? [closed]
Anyway what I am trying to figure out is something I have been thinking about for many years. The dinosaurs didn’t die from a big
explosion or anything just that the earths gravity increased and made ...
2
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2answers
126 views
How does earth carry moon with it, if it can not force moon to touch it by gravitational force?
earth's gravitational force is acting on its moon in such a way that it forces moon to rotate round its orbit by centripetal force and carries it while rotating round the sun by gravitational force. I ...
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1answer
254 views
In what limit does string theory reproduce general relativity?
In quantum mechanical systems which have classical counterparts, we can typically recover classical mechanics by letting $\hbar \rightarrow 0$. Is recovering Einstein's field equations (conceptually) ...
5
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0answers
87 views
Equation of state of cosmic strings and branes
I'm sure these are basic ideas covered in string cosmology or advanced GR, but I've done very little string theory, so I hope you will forgive some elementary questions. I'm just trying to fit some ...
2
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1answer
108 views
Sideways motion between a vertical launch from a planet and landing [duplicate]
I saw a video some days ago (Hello Kitty in Space) of a schoolgirl successfully launching a balloon into space which later popped and landed ~47 km from launch site.
If I vertically launch an object ...
1
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1answer
102 views
Will a plant grow faster or slower when affected with less/more gravitational forces
Will a plant grow faster when you would apply more upward gravitational force?
and/or
Will a plant grow slower when you would apply more downward gravitational force?
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1answer
132 views
How fast does water fall in the middle of a very very thick waterfall?
Let me create a very artificial experimental set up. Take a bathtub the size of Delaware and suspend it a mile above the ground. Fill it with water (though I'm not sure to what depth - and it might ...
1
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1answer
191 views
In what way is the Riemann curvature tensor related to 'radius of curvature'?
In Misner, Thorne & Wheeler, they say, in their delightful 'word equations' that
$$\left(\frac{\mathrm{radius\,\, of \,\,curvature}}{\mathrm{of\,\, spacetime}}\right) = ...
1
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1answer
105 views
What does it mean that Einstein's equations are hyperbolic-elliptical?
I says on Wolfram MathWorld that Einstein's field equations are a set of "16 coupled hyperbolic-elliptic nonlinear partial differential equations".
What does it mean that the equations are ...
1
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1answer
139 views
Do residents of the Hudson Bay area have more time?
Apparently there is a gravity anomaly in the Hudson Bay Area in Canada: gravity is "missing" or it is slightly less than it is in the rest of the world.
Does that mean that things in the Hudson Bay ...
2
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3answers
94 views
What is the relationship between the radius of a ring in a rotating space station and the strength of the artificial gravity generated?
Suppose engineers built a rotating space station similar to Space Station V from the film 2011: A Space Odyssey, but with multiple concentric rings where astronauts can live.
...
7
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3answers
468 views
Why is ski jumping not suicidal?
At least on television, ski jumpers seem to fall great vertical distances before they hit the ground - at least a few dozen meters, though I couldn't find exact distances via a quick search. And yet ...
1
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2answers
92 views
Why does gravity assist transfer twice the planet's velocity?
In orbital mechanics and aerospace engineering a gravitational slingshot (also known as gravity assist manoeuver or swing-by) is the use of the relative movement and gravity of a planet or other ...
2
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1answer
74 views
Degree of Time Dilation At a Distance From the Sun where acceleration = g?
At higher altitudes above a body, clocks tick more slowly, and gravitational field is weaker. But what is the relationship? It is tempting for a GR newbie such as myself to think that anywhere that ...
2
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2answers
156 views
London into Australia in 90 minutes
Me and my friend are having a debate on whether it would be possible for a human to travel at 15,000 miles an hour from London to Australia in the matter of 90 minutes. Would a human be able to ...
4
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1answer
102 views
Falling Electron
Suppose there are two objects in the universe. Earth, with a gravitational acceleration of g = 9.8m/s/s, and a typical electron.
The electron is dropped from a certain height, say 1000m above the ...
6
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1answer
179 views
Gravity duals to Navier Stokes and interpretation of non linear contributions
I have been reading the paper The Incompressible Non-Relativistic Navier-Stokes Equation from Gravity. In it they state,
"An instability, if it occurs, must necessarily break a symmetry ...
...
5
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3answers
208 views
Can low-gravity planets sustain a breathable atmosphere?
If astronauts could deliver a large quantity of breathable air to somewhere with lower gravity, such as Earth's moon, would the air form an atmosphere, or would it float away and disappear? Is there a ...
2
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2answers
52 views
Is it part of special relativity that mass possessing energy is more dense?
I was reading http://www.edge.org/3rd_culture/hillis/hillis_p2.html and it says that a charged battery weighs more than a dead one or a rotating object weighs more than a stationary one (i.e. mass ...
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2answers
189 views
What is a natural movement of a ball on a upward curve (the two arrow lines pointing upward) given no external force?
If you drop a ball down a upward curving parabolic ramp, what is the expected movement of the ball? Assume the ball is set into motion with no external force.
Would it go all the way from point A to ...
3
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4answers
575 views
Why does an object thrown parallel to the ground eventually fall down?
Suppose an object is thrown parallel to the ground. The gravity acts downward (ie. perpendicular to the direction of motion of the object). The work done by gravity on that object will be given by :
...
2
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1answer
83 views
Graviton and photons interaction
If one believes in the theory of gravitons then by viewing a black hole you see gravitons affect photons. This in turn leads to the conclusion that force carrier's mass equivalences allow them to be ...
2
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1answer
268 views
What does the graviton-matter Feynman scattering diagram look like?
The question is in the title really. I know gravity + QFT is on shaky ground but I'm not looking for Feynman rules, just a schematic, if that is possible.
Edit 1: added possible diagram for ...
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0answers
105 views
Did force of gravity cause macroevolution?
Did big bang create gravity?
What role gravity is assumed to have played in the formation (starting from the big bang) of large structures of our universe and what other important physical mechanisms ...
14
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7answers
593 views
Is the quantization of gravity necessary for a quantum theory of gravity?
The other day in my string theory class, I asked the professor why we wanted to quantize gravity, in the sense that we want to treat the metric on space-time as a quantum field, as opposed to, for ...
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2answers
476 views
Newtonian gravity vs. general relativity: exactly how wrong is Newton?
Is there a simple function I can use to describe the difference between simple Newtonian dynamics and the actual observed motion? Or maybe some ratios for common examples of, say, the motion of stars ...
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1answer
58 views
What the effect of gravity in the center of a planet feels like [duplicate]
Possible Duplicate:
Would you be weightless at the center of the Earth?
The issue of weightlessness at the center of the Earth has obviously already been discussed, however I am curious as ...
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1answer
57 views
Dense Spherical Black Hole Shell with a Region Inside
I'm going to propose a thought experiment, based on two ideas.
One: A uniform spherical shell, by the Shell Theorem, does not exert any gravitational force on objects existing in the interior of the ...
1
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3answers
121 views
What actually happens to a light ray on a Schwarzschild black hole horizon?
I know the Schwarzschild event horizon is a null surface generated by null geodesics. But what does that actually mean in terms of the path of a light ray that reaches it? Does that mean the geodesic ...
13
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2answers
268 views
Why aren't gas planets and stars fuzzy?
The edge of Jupiter looks very sharp.
Even more bothersome, the edge of the sun looks sharp, aside from kind of a soup of particles floating above it.
The sun's surface has an incredibly low ...
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3answers
259 views
If hydrogen and helium are lighter than air, why won't liquid hydrogen and liquid helium defy gravity?
Title says it all. If hydrogen and helium are lighter than air, why won't liquid hydrogen and liquid helium defy gravity?
2
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0answers
54 views
Was Einstein's Cross Predicted by Einstein's Theories? [duplicate]
Possible Duplicate:
How does gravitational lensing account for Einstein’s Cross?
Einstein's Cross is a fascinating phenomena for which I have asked explanation here. However, I'm also ...
3
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0answers
56 views
Gravitational effects and metric spaces
Could somebody please explain something regarding the Nordstrom metric?
In particular, I am referring to the last part of question 3 on this sheet -- about the freely falling massive bodies.
My ...
