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.
9
votes
5answers
287 views
What happens to light and mass in the center of a black hole?
I know that black holes are "black" because nothing can escape it due to the massive gravity, but I am wondering if there are any theories as to what happens to the light or mass that enters a black ...
4
votes
1answer
176 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 ...
1
vote
2answers
80 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
0answers
26 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
57 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
4answers
114 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 ...
10
votes
5answers
919 views
The square in the Newton's law of universal gravitation is really a square?
When I was in the university (in the late 90s, circa 1995) I was told there had been research investigating the $2$ (the square of distance) in the Newton's law of universal gravitation.
...
2
votes
3answers
61 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
1answer
60 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 ...
2
votes
2answers
47 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 ...
18
votes
4answers
1k views
Would you be weightless at the center of the Earth?
If you could travel to the center of the Earth (or any planet), would you be weightless there?
0
votes
1answer
65 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 ...
4
votes
1answer
57 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 ...
3
votes
2answers
85 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
64 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 ...
2
votes
2answers
450 views
Ski Jumper's vertical velocity after 246.5m record?
What would be the vertical velocity of this ski jumper (ski flyer), after he first touches down, after he breaks the record with a 246.5m jump? What g force would he experience as he slows down?
...
3
votes
2answers
214 views
What would happen if I take a glass of water in space?
What would happen if I take a glass of water in space i.e. outside the gravitational influence of earth?
My teacher said that the water would vaporize but I am not completely satisfied by the answer.
...
0
votes
0answers
15 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
84 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 ...
-1
votes
1answer
50 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
54 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 ...
0
votes
4answers
650 views
What is potential at a point?
What does potential at a point exactly mean? My teacher tells me that current flows from higher potential to lower potential but when I ask him the reason, he fails to give me a convincing answer.
...
1
vote
0answers
33 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
79 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
62 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
3answers
535 views
Why is a black hole black?
In general relativity (ignoring Hawking radiation), why is a black hole black? Why nothing, not even light, can escape from inside a black hole? To make the question simpler, say, why is a ...
7
votes
1answer
136 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 ...
1
vote
3answers
131 views
What truly is mass, and is there a direct way to measure it?
We know a mass of an object of one kilogram as an object that weighs W = mg = 9.8 N and we reference it to that, (when it should as a fundamental parameter describe weight not the opposite). But if we ...
1
vote
2answers
59 views
Can acceleration feel like constant gravity for indefinitely long?
So here's the setup: I'm in a spaceship, without windows as always, and the ship is accelerating upwards at a constant rate of $1\,\text{g}$. So inside the spaceship it feels like I'm being pulled ...
