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.
1
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2answers
38 views
Solar Catastrophe [duplicate]
Consider all of sudden the sun vanishes. What would happen to planetary motion. Will it continue to move in elliptical path or move in a tangential to the orbit immediately after sun vanishes or move ...
6
votes
1answer
100 views
Why is $R^2$ gravity not unitary?
I have often heard that $R^2$ gravity (as studied by Stelle) is renormalisable but not unitary. My question is: what is it that causes the theory to suffer from problems with unitarity?
My naive ...
0
votes
2answers
105 views
Einstein's theory tells us that gravity is a curve in space and time but how does that causes attraction in mass? [duplicate]
The sun is incredibly massive object and it causes the space around it to bend. This causes the planets to pulled to the sun or the planets move in an elliptical path around the sun. But I don't ...
1
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3answers
134 views
About gravity through space time curvature
Is it possible to produce virtual gravity? I mean gravity without the help of mass by curving spacetime with other effects like fast rotating objects?
2
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1answer
56 views
Can a rotating-ring space-station design be applied to a rotating sphere?
Suppose engineers built a rotating space station similar to Space Station V from the film 2001: A Space Odyssey (circa 1968), but with a large sphere, instead of a ring? Could this be rotated or ...
-1
votes
2answers
48 views
gravity affecting a molecules speed? [closed]
Why are the poles colder than the rest ofthe planet?Is the gravity stronger making molecules spin slower?How does gravity affect heat and hydrogen bonds? And what affects gravity?A little off topic ...
0
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2answers
90 views
Gravity pull on objects accelerating towards the earth's center?
Accelerating away from a mass mitigates gravity's pull on the accelerating object. Would the same be true for an object accelerating towards the center of the mass?
0
votes
0answers
60 views
How to calculate offset (lifting point) from Centre of Gravity (CG) to achieve a particular angle 26° [closed]
An object is suspended at a point at a distance of XXX from Centre of Gravity with two strings. The two strings are of equal length.
What should be the distance XXX to achieve 26° angle?
6
votes
2answers
146 views
Why water in the sink follow a curved path?
When you fill the sink with water and then allow the water to be drained, the water forms a vortex.. And then it starts to follow a curved path downwards by effects of gravity..
Why this phenomena ...
3
votes
2answers
131 views
Could a planet sized bubble of breatheable atmostphere exist?
I'm reading a book (Sun of Suns by Karl Schroeder) that the main location is a planet called Virga, which contains air, water, and floating chunks of rock, and has no or a very small amount of ...
2
votes
0answers
86 views
Finite or ∞ set of masses & ∃ gravity center?
Any finite & non empty set of masses has a computable center of gravity:
$\vec{OG} = \frac{\sum_i m_i \vec{OM}_i}{\sum_i m_i}$ .
Does the contrapositive permits to conclude that a mass system ...
1
vote
2answers
73 views
Gravity mitigated by velocity regardless of mass?
We know that a small object moving fast enough can pass by a planet and escape its gravity. Would this be (theoretically) true in reverse? Meaning a planet moving fast enough past a stationary smaller ...
2
votes
4answers
123 views
Does everything with mass or energy have a gravitational pull?
As small as it may be, does every 'thing' have a gravitational pull? That is, something with mass or energy. No matter how obsolete or negligible it may be, is it there? If so, how is it calculated? ...
2
votes
1answer
50 views
Simulations of Planetary Motions
I wrote a spreadsheet that simulates the trajectory of 3 planets in 2D space. The method is simple: for each moment in space, calculate the force felt and velocity of each planet, then for the next ...
1
vote
1answer
70 views
Is a purely vertical or almost vertical orbital launch possible?
Is it possible, for the sake of argument, to launch a payload into an orbit around the earth by putting almost all the energy going at a 90 degree angle? What velocity would it take, and what ...
0
votes
1answer
45 views
Gravitational potential energy
Consider two places next to each other: Place 1, where there is a gravitational field whereas Place 2 - there's no field.
Now if we lifted a box in place 1, it gains potential energy. Then, we move ...
3
votes
1answer
63 views
Would an object float if it were placed in the center of a rotating space station?
Suppose engineers built a large circular room in a rotating space station where if one looked directly up from any location, one could see the floor.
If one used a ladder to reach the center of the ...
1
vote
4answers
240 views
Why do objects accelerate as they fall?
Most importantly, what must change in order for the falling object to change its speed? Is it the distance to the centre of the planet? If you pull the earth away from the object as the object falls, ...
1
vote
1answer
108 views
Photon on null geodesic
If given an FRW metric
$ds^2 = -dt^2 + a^2(t)[dx^2+dy^2+dz^2]$
and for the trajectory followed by a photon (null geodesic; $ds^2=0$) with affine parameter $\lambda$, know that
...
0
votes
1answer
65 views
About the work done by gravity to pull the object down to the earth surface
The following question is from an physics exercise and I know the answer and the way to solve the problem but just curious why my own way doesn't work. The question is asking "A 2500kg space vehicle, ...
2
votes
1answer
65 views
Understanding bending light beam perpendicular to motion
I'm just reading a book about gravity. An example it gives is a spaceship accelerating. A beam of light travelling at right angles to the direction of movement of the spaceship enters it via a small ...
4
votes
1answer
169 views
Can a hovering helicopter travel half the globe in 12 hours? [duplicate]
Suppose we have a helicopter that is able to stay stationary in flight for extended periods of time. If such a helicopter stayed at point A in the sky for 12 hours straight, would it reach the other ...
1
vote
2answers
134 views
So gravity turns things round
It makes sense, since gravity tends to push the surface of a body towards it's center. Unless I'm mistaken, everything with mass has it's own gravity, every atom and for instance, our own bodies ...
0
votes
2answers
138 views
General Relativity & Kepler's law
According to Kepler's law of planetary motion, the earth revolves around the sun in an elliptical path with sun at one of its focus.
However,
according to general theory of relativity,
the earth ...
1
vote
2answers
97 views
Electric vs. Gravitational shielding [duplicate]
There are great similarities between electric and gravitational fields and, furthermore, a room can be electrically shielded so that there are no electric fields simply by surrounding it with a ...
0
votes
3answers
269 views
Force inversely proportional to the squared distance
Newton's law of universal gravitation:
"Newton's law of universal gravitation states that every point mass in the universe attracts every other point mass with a force that is directly proportional to ...
2
votes
5answers
238 views
Einstein gravity versus Newton's gravity
What's the basic difference between the gravity as seen by Einstein, and that by Newton?
0
votes
2answers
104 views
What mechanisms exist for generating lift on a static object?
What mechanisms exist for generating lift on a static object?
Condition is: Other than propellers
I know that generating lift on a static object in a sense of anti-gravity for e.g. drone is not ...
1
vote
1answer
81 views
What will be the shape of liquid if there is no gravitational force [duplicate]
We all know that liquid will take a shape of container in which its filled, but What will be the shape of liquid if there is no gravitational force?
0
votes
2answers
278 views
Generating artificial gravity by using rotation
If I want to design for futuristic space stations and I want to use rotation to produce
artificial gravity. One of such designs consists of a giant ring that is rotated about its centre. If it were ...
7
votes
1answer
124 views
Gravitationally bound systems in an expanding universe
This isn't yet a complete question; rather, I'm looking for a qual-level question and answer describing a gravitationally bound system in an expanding universe. Since it's qual level, this needs a ...
1
vote
0answers
30 views
In which direction does space “bend”? [duplicate]
Gravitation is often depicted as a ball on a cloth that curves a hole into space. But in what direction does this hole form? Into the direction the object is moving?
19
votes
3answers
571 views
Why is gravity such a unique force?
My knowledge on this particular field of physics is very sketchy, but I frequently hear of a theoretical "graviton", the quantum of the gravitational field. So I guess most physicists' assumption is ...
4
votes
2answers
132 views
Place each foot on a scale: can you add the two to find your weight?
I frequent a blog from a British psychologist, and every Friday he likes to pose an interesting puzzle or riddle. The Monday after that he posts the answer. They're good fun, and IANAP but this week's ...
3
votes
1answer
83 views
How can photons exert gravity if they are wave-like?
As a reference, see this question: Does a photon exert a gravitational pull?
It turns out the answer is "Yes" -- but this does not seem consistent with light being wave-like.
I am imagining a ...
0
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0answers
46 views
Flung out of the galaxy
I watched a video by Dr. Michio Kaku, in which he states a theory about Dark Matter.
This theory says that Dark Matter could be just ordinary matter from another parallel universe, which would be ...
3
votes
2answers
89 views
Gravitational distortion of an object's diameter, at a distance,
Does the curvature of space-time cause objects to look smaller than they really are? What is the relationship between the optical distortion and the mass of the objects?
0
votes
1answer
58 views
Geodetic model for numerical weather prediction
What is the implicit geodetic model used by common numerical weather prediction products? WGS84? NAVD88?
For example, NOAA's Rapid Refresh (RAP), North America Mesoscale (NAM), and Global Forecast ...
3
votes
1answer
94 views
Are laws of gravity time symmetric?
Time symmetry is often explained by the example of orbiting objects... What I can't find an explanation for is the moment when an object enters into orbit around another object. That clearly breaks ...
3
votes
1answer
151 views
Calculating Riemann Tensor Using Tetrad Formalism
I was trying to calculate the Riemann Tensor for a spherically symmetric metric:
$ds^2=e^{2a(r)}dt^2-[e^{2b(r)}dr^2+r^2d\Omega^2]$
I chose the to use the tetrad basis:
$u^t=e^{a(r)}dt;\, ...
2
votes
1answer
149 views
Newton's Law of Graviation: Why G?
I've been wondering, in Coulomb's Law, $k_e = \dfrac{1}{4\pi\epsilon_0}$. Therefore, why do we use $G$ in Newton's Law of Gravitation? What if the constant is more like Coulomb's Law, e.g.
$G = ...
1
vote
4answers
87 views
Constructing an orbital trajectory that quickly returns to its origin
I'm working on a science fiction story that involves two spaceships engaged in combat while in orbit around a planetoid. My original idea called for spaceship A to trick spaceship B into firing a ...
-3
votes
1answer
102 views
why gravity exists? [closed]
I always have a doubt on gravity , why does gravity exists ?
is there any scientific explanation on gravity ?
I know that Gravity exists , i can feel it. But Who is creating all these rules ?
...
2
votes
1answer
37 views
Reconciling Units in Jeans' Criterion Formula
In "Physics and Chemistry of the Solar System" Jeans' Criterion is given as:
$\frac{GmM}{R_c} = \frac{3mkT}{2}$
... To me this suggests that on the left we have Joules, and on the right we have ...
0
votes
4answers
284 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 ...
0
votes
0answers
45 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
votes
3answers
114 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 ...
0
votes
1answer
102 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 ...
0
votes
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 ...
3
votes
3answers
204 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 ...
