Tagged Questions
2
votes
1answer
54 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 ...
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 ...
-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
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
vote
5answers
138 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 ...
1
vote
4answers
251 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
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
3answers
280 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
246 views
Einstein gravity versus Newton's gravity
What's the basic difference between the gravity as seen by Einstein, and that by Newton?
7
votes
1answer
126 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 ...
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 = ...
3
votes
3answers
214 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 ...
1
vote
3answers
258 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
votes
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 :
...
0
votes
2answers
469 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 ...
1
vote
1answer
130 views
How to calculate gravity inside the star?
Gravity must decrease due to less effective mass when going inside the object but also must increase with depth inside the star due to its higher density. Is there a model or formula approximating ...
0
votes
2answers
244 views
How Newton found Gravitational acceleration?
How Newton found Gravitational acceleration (g) of The Earth?
Can you describe the methods to find and prove it(g value)?
(may be describe both classical methods and modern methods)
0
votes
1answer
108 views
What is the gravity at the center of the Earth? [duplicate]
Possible Duplicate:
Would you be weightless at the center of the Earth?
Supposing there is a cavity at the center of the Earth, what is the gravity there? What will be its direction and ...
2
votes
2answers
147 views
Is the gravitational constant G a minimum value in some sense?
Assume a central body of mass $M$, and call $a$ the acceleration of a test
body at a distance $r$ due to any interaction whatsoever with the central
body. Is is correct to say that the ratio $a r^2/ ...
1
vote
5answers
248 views
Electro-gravitation - is it real?
I came across an article claiming that if you charge two plates, one positive and one negative, and fasten them together (assuming they are insulated from each other), they will float in the air. I ...
0
votes
1answer
174 views
Gravitational force?
We know that two mass particle attract each other with a force
$$F~=~\frac{G M_1 M_2}{r^2}.$$
But what is the reason behind that? Why does this happen?
0
votes
2answers
272 views
When we throw an object in the presence of gravitational attraction is the mass of the object proportional to the time of fall or not?
I was confused when i saw two object of different masses (A and B)falling from the same height(h) but both of them strikes the ground at same time. Is this possible, that masses of the objects are ...
2
votes
2answers
796 views
How gravitation effect on tides
I know that tide is caused by the gravitational pull of moon but what I don't know is how it effects on water. I have actually these doubts.
Why does gravity of the moon creates tides only in water?
...
3
votes
1answer
384 views
Gravitational attraction of triangles
Suppose I have two triangles relatively close together (so they probably shouldn't really be treated as point masses). I want to calculate the gravitational force (and potentially torque?) generated ...
10
votes
5answers
940 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.
...
0
votes
3answers
553 views
Still trying to understand gravitational potential and Poisson's equation?
A week or so back I asked a question about the gravitational potential field
$$\phi=\frac{-Gm}{r}, \qquad r\neq 0, $$
and how to show the Laplacian of $\phi$ equals zero for $r\neq 0$? Eventually, ...
1
vote
2answers
160 views
Why no basis vector in Newtonian gravitational vector field?
In my textbook, the gravitational field is given by$$\mathbf{g}\left(\mathbf{r}\right)=-G\frac{M}{\left|\mathbf{r}\right|^{2}}e_{r}$$
which is a vector field. On the same page, it is also given as a ...
3
votes
1answer
408 views
Trying to understand Laplace's equation
I'm struggling here so please excuse if I'm writing nonsense.
I understand that the gravitational potential field, a scalar field, is given by $$\phi=\frac{-Gm}{r}$$
where $\phi$
is the ...
2
votes
1answer
571 views
Simulating Gravity in 3D Game?
Alright, I am writing a space simulator for a 3D game and I would like to implement gravity of objects into it.
Is there a nice way to find a velocity vector which can be added to my engine output ...
6
votes
4answers
617 views
Can gravity be shielded, like electromagnetism?
If I remember well, they said that it can't, but I do not know why.
Yes, I meant if gravity can be shielded using something like a Faraday cage
(or something else?).
Thank you.
5
votes
2answers
646 views
Calculating gravity when taking into account the change of gravitational force
This is a problem that has bothered me for a couple of weeks now, and I can't seem to wrap my head around it and understand it.
Let's say we have a planet with a mass of m. We also have an object of ...
3
votes
4answers
390 views
Can a black hole be explained by newtonian gravity?
In the simple explanation that a black hole appears when a big star
collapses under missing internal pressure and huge gravity, I can't see
any need to invoke relativity. Is this correct?
1
vote
2answers
76 views
Can a photon passing by an open space barycenter of a system of masses be modeled as if all the system's mass is at the barycenter?
To be clear, this example can't apply to the Solar System, since the barycenter is within the Sun, similarly the Earth/Moon system's barycenter is within the Earth.
But, given a system of ...
6
votes
7answers
1k views
How does Newtonian gravitation conflict with special relativity?
In the Wikipedia article Classical Field Theory (Gravitation), it says
After Newtonian gravitation was found to be inconsistent with special relativity, . . .
I don't see how Newtonian ...
2
votes
0answers
138 views
Calculation of a Gravity Resonance Keyhole
Can anyone describe the mathematics behind the calculation of a resonance keyhole (for a two-body model)? It seems like the size and position of the keyhole should be a function only of mass and ...
3
votes
4answers
351 views
Can a disk like object (like UFO's) really fly?
UFOs as shown in movies are shown as disk like objects with raised centers that emit some sort of light from bottom. Can such a thing fly?
My very limited knowledge in physics tell me that a disk ...
4
votes
4answers
179 views
Are Newton's gravity waves detectable by a laser interferometer?
Newton's theory of gravity supports "gravity waves" in that moving objects cause changing gravitational fields. For example, two bodies rotating around their center of mass will have a stronger ...
11
votes
3answers
808 views
Significance of the second focus in elliptical orbits
1.In classical mechanics, using Newton's laws, the ellipticity of orbits is derived. It is also said that the center of mass is at one of the foci.
2.Each body will orbit the center of the mass of ...
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?
4
votes
8answers
5k views
Is gravity a force and if so what is its opposite?
For every force there is an equal force in the opposite direction on another body, correct?
So when the Suns gravity acts on Earth where is the opposite and equal force? I also have the same ...
8
votes
6answers
1k views
Is Newton's Law of Gravity consistent with General Relativity?
By 'Newton's Law of Gravity', I am referring to
The magnitude of the force of gravity is proportional to the product of the mass of the two objects and inversely proportional to their distance ...
