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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164 views

How to calculate the velocity needed for a rocket to get to a L1 point (escape a body without orbiting)?

I'm looking to calculate parameters around launching, say, a model rocket STRAIGHT to the moon. This does not mean through orbital insertion into a stable ~17,000 MPH relative to earth's surface and ...
0
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0answers
35 views

Gravity propagation speed [duplicate]

Related to: The speed of gravity? In the related question and in many other questions here, it seems as if the propagation speed of the gravitational interaction is $c$. To my understanding, the only ...
0
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0answers
49 views

Degrees of freedom in physical equations

Say we have the field equation: \begin{equation} f^{\prime}(R)R+3\square f^{\prime}(R)-2f(R)={\kappa}^{2}T, \end{equation} why is the non-vanishing of the second term means that there is an extra ...
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2answers
55 views

A small object on the opposite side of the earth's orbit with 0 velocity,“in line” with the core - would it collide with the earth?

If a small object (say mass 1 kg), at the opposite side of the earth's orbit (six months away), was placed in the same orbital position as the earth's core, at zero velocity in all directions, would ...
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0answers
63 views

Einstein frame vs. Matter frame

What is the difference between Einstein frame and Matter frame in General Relativity? -A brief comment on each could be useful too. These two frames were used in this manuscript ...
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1answer
61 views

Minimal vs. Non-minimal coupling

What is the difference between Minimal vs. Non-minimal coupling in General Relativity? A brief introduction to Minimal Coupling in General Relativity could be useful too.
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1answer
82 views

What's the reason behind Earth's gravity? [closed]

How can Earth attract any object irrespective of what it is made?
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1answer
50 views

is gravity instant? [duplicate]

some one states that the earth would travel in it path for 8 min if the sun vanished. The equations of gravity show the Moon would crash into the Earth and the Earth would head for Mars the instant ...
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0answers
40 views

Topology of spacetime in 2+1 dimension

In the book Quantum Gravity in 2+1 dimension by S. Carlip, in the second chapter (section 2.1), he comments that a compact 3-manifold with a flat time orientable Lorentzian metric and a purely ...
0
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2answers
76 views

Force acting on center of mass

Pictured above is a biker (traveling in a curve) whose center of mass has two forces acting on it. These two forces - a horizontal centrifugal force F(centripetal)* and a vertical gravitational ...
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2answers
84 views

What happens to gravity in the middle of the earth? [duplicate]

So I was curious about, what if we make a tunnel from one side of the earth, to the other side of the earth? Gravity is ofcourse always negative, which makes you "fall" and not "float". If we take ...
0
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1answer
21 views

Inhomogeneties in gravitational acceleration at the surface of the Earth.

I am looking for data sets which clock the time and precise location of free falling bodies in a vacuum. I have been told that the acceleration of gravity is not absolutely 100% uniform, and I would ...
4
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1answer
137 views

Why would a pendulum experiment give $g > 9.8\ \mathrm{m/s^2}$?

I am taking an introductory lab course in which we've done an experiment on the physical pendulum. We've seen that for small oscillations, the period is ...
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3answers
126 views

Questions about spacetime curvature and gravity

These are some further important queries regarding the question here Why would spacetime curvature cause gravity? Q1. Explain the statement “Everything in spacetime moves at the speed of light”. Is ...
51
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4answers
5k views

Why would spacetime curvature cause gravity?

It is fine to say that for an object flying past a massive object, the spacetime is curved by the massive object, and so the object flying past follows the curved path of the geodesic, so it "appears" ...
8
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1answer
669 views

Why quantising gravity necessarily give us gravitons?

Gravitons are supposed to be the quanta of gravitational field My question is, if we do not know how to quantize gravity yet, how do we know that quantizing it in principle should give us gravitons, ...
3
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0answers
39 views

entropy relation between ads$_2$ black hole and near extremal ads RN black brane

It seems that the entropy for AdS$_2$ black hole is independent of the temperature $s=s_0$. While for near extremal AdS RN black brane, $s=s_0+ s(T/\mu)$. Should not these two entropies be the same ...
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0answers
49 views

Object that causes spacetime to expand?

Is there any thing that will cause spacetime to expand, so that particles are pushed away from them rather than pulled towards it. I know things such as black holes and planets causes dips and curve ...
0
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1answer
107 views

General relativity, gravity and spacetime curvature [duplicate]

There is a very fundamental flaw in the common explanation given of the space-time curvature due to massive objects. It is said that a massive object curves space time just like a bowling ball on a ...
1
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1answer
38 views

Smaller mass in gravity well?

When sitting in a gravity well, as we do on earth, does our effective mass become smaller than our rest mass due to having negative potential energy? Correspondingly, does a free falling mass (from ...
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0answers
29 views

How to measure power used to sustain something in a (gravitational) field? [duplicate]

I've read this question and answers, but neither of the posts does seem to address my concerns. The problem is as follows: Assuming a device that keeps something in a gravitational field on a ...
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0answers
26 views

Physical difference between the derivative of the Hubble parameter and the second derivative of the scale factor?

In Carroll's GR book, he discusses the difference between $\dot H$ and $\ddot a$, stating that they are the answers to two different questions, pg. 349. He seems to imply that if one set up two ...
5
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2answers
85 views

Speed of gravity in cosmological codes and ephemeris generation

There are few questions in Phys.SE concerning the speed of gravity, and the answers are traditionally that the speed of gravity equals to the speed of light. But in that case I have three more ...
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3answers
88 views

In what situations do water levels not reach equilibrium?

I have been taught that water levels will always equal out. However, now I find that sumps and some other setups allow for water not to become equal. What other arrangements allow for the water levels ...
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1answer
67 views

The nature of the gravity force: Is it attractive or repulsive between positive and negative mass? [duplicate]

If negative mass is rotating around fixed positive mass, then what will be the nature of force and how?
1
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1answer
61 views

Does gravity have any effect on sound waves? [duplicate]

If gravity at a place increases or decreases, does it affect the sound wave propagating through that place. If for certain place gravity increases on earth will there be change in direction or ...
2
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4answers
71 views

about the rotation of the earth and gravity, when all continents were merged

A long time ago, I read that the gravity force isn't the same if you are near the Andes Mountains or if you are at Paris. So today I asked to myself if when all continents were one, if the difference ...
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1answer
21 views

Shock Absorber - Bus - Not Uniform

Imagine a empty bus/lorry travelling at high speed over the "speed brake", why is that only rear seat is heaved relatively high compared to the fron seat?
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1answer
23 views

How much time would take to lift a person to 0.1m above floor of elevator? [closed]

How much time would take to lift a person to height $h$ above floor of elevator if the elevator goes down with acceleration $a$, where: $$h=0.1 \; \text{m}$$ $$ a=13 \; \text{m}/\text{s}^2 $$ How to ...
2
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0answers
76 views

How far could the LHC “fire” a particle

Very simple question, and frankly quite a silly one, but I'm currently writing a lecture for secondary school kids and I'd love to tell them how far the Large Hadron Collider could fire a proton. The ...
4
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1answer
86 views

Setting $\delta R =0$ on boundary of hypersurface

Does requiring $\delta R=0$ on the boundary of hyper-surface create any restrictions or problems in deriving the field equations from Einstein-Hilbert Action?
0
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1answer
61 views

The Shell Theorem and A Problem Related to it

The shell theorem states that: A uniform spherical shell of matter attracts a particle that is outside the shell as if all the shells mass were concentrated at its center. Now, I have to solve a ...
0
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2answers
109 views

Gravitational compression in the atmosphere

One of the two sources of Earth's heat is primordial heat, which is the product of gravitational compression and impacts during Earth's formation. My understanding is that work is done on the core, ...
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2answers
104 views

Is it possible to have a negative attraction to gravity just like how magnets with same pole does?

Layman question here, is it possible for an object to be negatively attracted to a gravitational pull of another object? Like how same pole magnets repels each other, can it happen on gravity too?
2
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1answer
47 views

why galaxies look like discs rather than spheres? [duplicate]

Black holes have much gravitation to hold all stars and nebulas but why they are aligned in disc type shapes rather than spheres because gravitation is everywhere around black holes. Even on upper ...
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2answers
205 views

How does time dilate in a gravitational field having a relative velocity of v with the field?

Consider a Mass on earth. The time dilation on the surface of Earth is $$T' = T \sqrt{1 - \frac{2GM}{rc^2}}$$ Now if the mass is moving around the earth at velocity of v w.r.t Earth, what will be ...
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1answer
59 views

Finding the constant of gravity in a game [closed]

Minecraft is a game of mining where one digs and finds ore (to put it simply). the world is composed of "blocks" 3 dimensional cubes that have different "pictures" on them, that make them appear like ...
5
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2answers
107 views

What is the energy required to create mass of m at a height of h above the Earth?

What is the energy required to create mass of m at a height of h above the Earth? Is it $E= m c ^2$ or $E = mc ^ 2 + mgh$ ? Let's reverse the process also. If you convert mass $m$ at $h = 0$ to ...
6
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4answers
935 views

If you could ride an elevator through the earth [duplicate]

What if it was possible to ride an elevator straight through earth. If we take all the heat and pressure problems away, and assume it would be possible: What would happen with gravity? Would gravity ...
3
votes
3answers
214 views

Why meet at the center of mass?

If two objects of different masses are held at a distance $d$ and then I let them go, they will meet at the center of mass of the particle system due to mutual gravitational attraction My question ...
3
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2answers
107 views

Light & Observer moving perpendicular to each other

Light is the yellow arrow. Observer is the black arrow. Observer is moving at a constant speed of v, w.r.t to a Galilean frame of reference. Now from the point of view of the observer (O), how ...
10
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2answers
264 views

The problem of self-force on point charges

Allow me to preface this by stating that I am a high school student interested in physics and self-studying using a variety of resources, both on- and off-line, primarily GSU's HyperPhysics website, ...
3
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1answer
94 views

How much weight can a person carry to avoid being blown over by wind?

I wonder if there is a certain amount of weight that I could carry in a rolling bag to help prevent me from being knocked over by the wind. I have balance problems and some lack of muscle strength in ...
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0answers
40 views

Find the Earlier time at half maximum height and Later time at half maximum height [closed]

You throw a baseball directly upward at time t = 0 at an initial speed of 12.1 m/s. What is the maximum height the ball reaches above where it leaves your hand? At what times does the ball pass ...
0
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2answers
67 views

Helium Balloon Experiment

We tied a helium filled balloon to a counterweight and it floats aimlessly in the room. I asked if the balloon were to be outside the building (all things considered no wind same temperature) would ...
4
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3answers
105 views

Using 2D position, velocity, and mass to determine the parametric position equations for an orbiting body

I have a gravity-related question. I am programming an orbit simulator. I have everything up and running, but I would like to render the smaller body's orbital path (the larger body is fixed). To do ...
0
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0answers
51 views

How do I measure the total weight of a container with scales on four corners?

I have a very large movable trash container, and I have mounted four scales, one on each corner. How do I get the total weight of the entire container? Is it simply a sum of the four weights, or is it ...
2
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2answers
129 views

Is there a delay in the effect of gravitational force?

Let's suppose there is a very massive object and a small object that are 1 lightyear apart. The massive object is large enough that the gravitational force pulling the small object is easily ...
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2answers
43 views

What is the constant $g_0$ used for calculating the specific impulse in seconds?

Wikipedia defines specific impulse as: $$ I_\mathrm{sp} = \frac{F_\mathrm{thrust}}{\dot{m} \cdot g_0} $$ The $g_0$ is said to be the acceleration at the Earth's surface. So is it actually the ...
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2answers
101 views

Does gravity cause spacetime to bend? [closed]

Does gravity cause spacetime to bend even though space has no mass?