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.
3
votes
3answers
140 views
How does relativity explain gravity, without assuming gravity [duplicate]
I have seen the "objects pull down on space-time" explanations, but they assume a "pull down" force themselves. Could anyone explain the space-time explanation without assuming gravity in the first ...
0
votes
1answer
37 views
How does gravity effects both time and light if they have no mass [duplicate]
I've been reading about how black holes can effect both time and light with gravity. So I was wondering, doesn't something have to have mass to be effected by gravity? And if so, does this mean both ...
2
votes
1answer
45 views
Questions about the Jeans length
I have a couple of questions about the Jeans length. Suppose the universe has a homogeneous energy density, except there's a spherical region that is overdense.
I understand that if the region is ...
-2
votes
0answers
39 views
Whats the theoretical max speed to go around the world? [closed]
I light of the new Scramjet tests I have a question thats been bogging me.
I live in Denmark, about the furthest i can travel is to New Zeeland which is roughly on the opposite side of the earth.
...
2
votes
1answer
50 views
Acceleration due to gravity?
I was looking into orbitals and found something I haven't been able to understand.
http://www.math.ubc.ca/~cass/courses/m309-01a/hunter/satelliteOrbits.html
There is a part on the page which states ...
0
votes
1answer
88 views
can be exist the negative mass? [duplicate]
I'm not sure about this but I guess there must be negative masses in the universe because of the symmetry. If the gravity is one of the main forces in nature it must has negatives mass to be able to ...
1
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1answer
28 views
Can we build a synthetic event horizon?
If we imagine ourselves to be a civilization capable of manipulating very heavy masses in arbitrary spatial and momentum configurations (because we have access to large amounts of motive force, for ...
2
votes
0answers
33 views
The gravitational random walk
When we shoot a single photon out into space, the chance that it will eventually return to our vicinity from a different direction is vanishingly small, even though spatial curvature exists due to the ...
-8
votes
0answers
59 views
Are Dark Energy, Dark matter invented concepts to cover up our lack of understanding? [closed]
Dark Energy?, Dark matter? mean two entities that we have no proof of its existence, we do not know what they are and we just invented those names to cover up what we do not know or understand, while ...
0
votes
2answers
102 views
What is a “gravitational cell”?
I am not a physicist, and I don't understand the details of electromagnetism. Anyhow, I was looking for how the batteries work in Google. So, I came across this article: "How batteries work: A ...
-1
votes
1answer
60 views
Earth and Moon computer simulation [closed]
So I want to simulate the solar system but want to start simple with one orbiting body.
However, I never did anything like this before and was wondering if anyone here could give me some hints.
...
6
votes
2answers
131 views
What are the limitations of performing music in space?
Canadian astronaut Chris Hadfield's song Space Oddity is making news around the world today. It makes me wonder: What are the limitations of performing music in space? Clearly, there is no point to ...
1
vote
1answer
53 views
Defining the star as the ellipse focus rather than the barycenter, what does the other focus do? [duplicate]
There are a lot of images and animations on the internet depicting two bodies orbiting around their common barycenter. The barycenter is defined as the (let's say right) focus of the ellipse.
If we ...
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2answers
51 views
If there were two equal masses with one mass in the middle which way would gravity pull it?
If there were two masses with a third exactly in the middle of those two, which way would the middle mass be pulled?
2
votes
1answer
62 views
Physics of a cold and hot top
Imagine two tops made up of exactly one thousand atoms. One is kept at 4 degrees Kelvin, the other at room temperature.
1. Would they weigh the same given an arbitrarily precise scale in the Earth's ...
10
votes
1answer
1k views
Does a guitar sound different in zero (or micro) gravity?
Seeing a video of astronaut Chris Hadfield playing a guitar on the International Space Station made me wonder if a guitar or other stringed instrument played in zero-G would sound any different than ...
-8
votes
0answers
42 views
not all items fall at the same rate some items have outside facters gain speed in which they “fall” [closed]
I was reading one of the post this morning and found it fasanating with all the formulas that were being poured out about items will falling at the same rate given the same hight that they were droped ...
1
vote
1answer
82 views
Initial position and velocity of rocket to escape earth's gravity
I'm trying to numerically simulate a spacecraft trajectory between earth and mars. I already wrote the solar system model where the sun is at the origin of the x,y,z plane Earth and Mars are orbiting ...
13
votes
1answer
146 views
Is period of rotation relative?
My question is inspired by the following answer by voix to another problem:
"There is a real object with relativistic speed of surface - millisecond pulsar. The swiftest spinning pulsar currently ...
1
vote
2answers
104 views
Negative potential energy of gravity
Does the negative potential energy in the gravitational field have to be considered in calculating the total mass of the system in question (because of $E=mc^2$)?
If so it seems to me that the ...
-2
votes
2answers
94 views
Repulsion does not exist; Gravity assist slingshot as a repulsive force [closed]
unification theory might say that there is only one force in universe that is called gravity(attraction).
So at atomic level for same charges that repel eachother(electrons etc.), if thought of as a ...
2
votes
2answers
88 views
Why don't black holes within a galaxy pull in the stars of the galaxy
visit http://www.nasa.gov/audience/forstudents/k-4/stories/what-is-a-black-hole-k4.html
If black holes can pull even light, why cant they pull the stars in the galaxy?
0
votes
0answers
69 views
Is there any proof that the speed of gravity is limited? [duplicate]
I must warn that though I'm argumenting with black holes I'm not asking how does gravity escape the black hole!. I want to know if the absolute speed of gravity waves were proven bu an experiment.
We ...
10
votes
2answers
272 views
Does relativistic mass have weight?
If an object was sliding on an infinitely long friction-less floor on Earth with relativistic speeds (ignoring air resistance), would it exert more vertical weight force on the floor than when it's at ...
4
votes
1answer
52 views
Gravitational resonances for satellites
I read on the website of European Space Agency that the altitude of Galileo satellites, which is 29600 Km from the center of the Earth, is chosen to avoid gravitational resonances so that station ...
4
votes
1answer
58 views
How would gravity change on a planet rotating around itself very fast?
Let's take a planet identical to Earth, but with rotation speed multiplied by ten thousand. What would happen with the gravity if it was spinning madly around itself? Would the centrifugal force make ...
0
votes
2answers
74 views
Will a helicoper which is hovering inside a closed box move with the box when we move it? [duplicate]
I got this micro helicopter to play with, you know that cheap double bladed ones you can find for $25 or so. Anyway last night I was on bed trying to sleep and I got this idea, what if we put the ...
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votes
1answer
81 views
Is the speed of light related to the mass of the universe?
If the mass of the universe were cut in half, would it affect the speed of light?
Would it be twice as fast?
Would it stay the same?
Do we have instruments that are sensitive enough to measure the ...
-6
votes
4answers
342 views
Violation of Newton's Second Law (?)
Here the big circle denotes the circular path of a stone(small circle on path) tied to a string from the centre of the circular path .
This is COMPLETELY HORIZONTAL
At an instant the velocity in ...
-3
votes
0answers
36 views
effect of gravity on chemical reaction rates [closed]
a chemical reaction is done on earth in very vacuum and that chemical reaction is also done in space so that gravity higgs field not affect that reaction.
Which reaction will be fast wrt gravity and ...
1
vote
2answers
91 views
What happens to things when things get crushed in a blackhole [duplicate]
When a black hole destroys things until they are smaller than molecules, where does it go and what happens when it clogs up?
1
vote
2answers
79 views
The potential and the intensity of the gravitational field in the axis of a circular plate
Calculate the potential and the intensity of the gravitational field at a distance $x> 0$ in the axis of thin homogeneous circular plate of radius $a$ and mass $M$.
Could anybody describe how to ...
-1
votes
1answer
72 views
The effects of heat on gravitational fields
In boiling soapy water, globs of soap coalesce as the temperature increases to boiling. Does this mean that temperature increases the gravitational pull of bodies?
1
vote
5answers
137 views
How universal gravitation falls short
As a non physicist I can understand how Newtonian mechanics falls short in cases of high velocity etc. and is properly generalized by the special theory of relativity.
What is not clear to me is how ...
2
votes
3answers
72 views
What is the cause the light is affected by gravity? [duplicate]
I know that photons have no mass and that a photons exist only moving at the speed of light. So what is the cause that a massive astronomical object can bend a ray of light?
I have two thoughts, but I ...
2
votes
2answers
49 views
Can the effects of a person's mass upon the local gravitational field be detected and measured remotely?
As the title suggests, Can the effects of a person's mass upon the local gravitational field be detected and measured remotely?
I am aware any mass produces and effects gravity but couldn't find ...
4
votes
1answer
66 views
Orbital mechanics and rocketry: Is it ever a good idea to intentionally lower periapsis?
tl;dr: Hohmann Transfer appears to be the optimal way to achieve a circular-to-circular orbit, but is it possible to lower the periapsis in order to achieve a more elliptical orbit with apoapsis at ...
4
votes
2answers
98 views
What is the fastest a spacecraft can get using gravity-assist?
Assuming normal spacecraft and space objects (no neutron stars, black holes, etc). To what speed can a spacecraft accelerate using gravity-assist?
For example, if a spacecraft is moving at ...
1
vote
2answers
84 views
What happens when a star undergoes gravitational collapse?
Immediately prior to becoming a supernova the core of some types of stars may suffer gravitational collapse.
What happens to any planets in orbit around the star at the instant the mass is fully ...
7
votes
5answers
478 views
Why do we still need to think of gravity as a force?
Firstly I think shades of this question have appeared elsewhere (like here, or here). Hopefully mine is a slightly different take on it. If I'm just being thick please correct me.
We always hear ...
0
votes
0answers
16 views
Gravity versus light [duplicate]
I've read this problem somewhere but don't remember where I saw it, but anyways...
So Earth revolves around the sun, and let's hypothetically remove the sun (make it disappear) would Earth just ...
0
votes
0answers
20 views
Some basic questions about electric field & nucleus [duplicate]
I am not good in physics.You can say I am beginner in this field.
I have some basic questions.
I ju st want to know that
[1] If there is repulsive force between same charges proton-proton then why ...
0
votes
2answers
95 views
What is the mass of a photon moving at the speed of light? [duplicate]
What is the mass of a photon moving at the speed of light?
And if it does not have mass, how is it affected by gravity?
Also why does Einstein's general relativity support that a gravitational wave ...
0
votes
1answer
82 views
Energy needed to lift and bring down an object
A mass of 0.5 Kg needs to be moved from point A to another point (B) which is 1 meters above point A. The time for this movement should be 0.2 seconds, then the mass is kept at position B for another ...
-1
votes
1answer
53 views
What is mathematical definition of a strong gravity?
Mathematical definition of a weak gravity is simple $g=\frac{GM}{r^2}$
but what is mathematical definition of a strong gravity? (blackhole-like or close to a blackhole-like object)
0
votes
1answer
56 views
Gravity in stone
I want to ask is it possible for a stone to have some magnetic power different from power that we see in ordinary metal magnets (something like earth gravity that attract everything). Someone told me ...
1
vote
0answers
37 views
When spacetime expands to the point where galaxy clusters are not observable, will there by any interaction?
It's my understanding that in a few billion years, clusters of galaxies won't be able to directly observe one another due to the expansion of spacetime overcoming gravity between those clusters. ...
3
votes
2answers
85 views
Orbit in the vacuum
As the space is a vacuum and there is no friction in space,
Can we assume that, if we place an object in gravity in exactly the right distance from a planet with gravity and in the right acceleration, ...
3
votes
2answers
74 views
Regarding the free electrons on the conductor
In a metal, why don’t the free electrons fall to the bottom of the metal due to gravity?
Also, charges in a conductor are supposed to reside on the surface so why don’t the free electrons all go to ...
7
votes
1answer
148 views
Why is Einstein gravity not renormalizable at two loops or more?
(I found this related Phys.SE post: Why is GR renormalizable to one loop?)
I want to know explicitly how it comes that Einstein-Hilbert action in 3+1 dimensions is not renormalizable at two loops or ...
