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.

learn more… | top users | synonyms

0
votes
3answers
1k views

If hydrogen and helium are lighter than air, why won't liquid hydrogen and liquid helium defy gravity?

Title says it all. If hydrogen and helium are lighter than air, why won't liquid hydrogen and liquid helium defy gravity?
2
votes
0answers
56 views

Was Einstein's Cross Predicted by Einstein's Theories? [duplicate]

Possible Duplicate: How does gravitational lensing account for Einstein’s Cross? Einstein's Cross is a fascinating phenomena for which I have asked explanation here. However, I'm also ...
3
votes
0answers
72 views

Gravitational effects and metric spaces

Could somebody please explain something regarding the Nordstrom metric? In particular, I am referring to the last part of question 3 on this sheet -- about the freely falling massive bodies. My ...
1
vote
2answers
344 views

Where inside a large uniformly dense, symmetrical sphere would its gravity toward the center be the strongest?

Imagine a sphere of uniform density with similar volume and average density of our Earth. There is a bore leading to the center of the sphere from the surface with a scale at regular intervals. At ...
2
votes
1answer
91 views

Time taken for gravity of a distant object to interact with a newly created particle? [duplicate]

Possible Duplicate: The speed of gravity Does gravity travel at the speed of light? Imagine there is a large mass $m_1$ (e.g. a star) 1 light-year away from us. It is stable, stationary ...
0
votes
1answer
53 views

Gravitational potential energy with regards to annihilation

Given particles A, B, C and D, where: A and B have an equivalent mass C and D have an equivalent mass, both larger than A (or B) D is the antiparticle of C. A and B start close to C, but with ...
2
votes
1answer
794 views

Calculating projectile range from known maximum height and time traveled

I've been stuck on this problem for many hours and I think I'm onto the right solution but I'm uncertain about my math. I've got a projectile that I know its maximum height and it's hang time and I ...
3
votes
2answers
156 views

Does the Earth have a semi-solid body at its core because of lower pressure at the center of the Earth?

I have read that the Earth has a semi-solid iron body at its core, even though that object is surrounded by liquid magma.... I'm wondering if this is because of a pressure (and resulting temperature) ...
4
votes
4answers
461 views

Gravity from a singularity as distance approaches zero

If you had a singularity (that had mass but took up no space), what would happen to the acceleration of an object as it approached this singularity? I would assume that it would be infinite, since as ...
0
votes
2answers
674 views

Bowling ball on a rubber sheet analogy - what pulls the ball down [duplicate]

Possible Duplicate: Does the curvature of spacetime theory assume gravity? Since I read Cosmos long ago, I see the same analogy about the balls rolling on a rubber sheet used to explain how ...
0
votes
1answer
173 views

If there was no Earth, what would be the acceleration of gravity from here from the Sun?

Suppose there were no Earth to pull us back and we're hanging in the solar system. Assuming no other force of gravity from other bodies, what would be the $g$ from the Sun?
0
votes
2answers
299 views

Measuring work done by gravity over non-constant gravitational acceleration

A question from an example from a MIT Classical Mechanics Lecture on Work. Here's the given definition for gravitational potential energy (~32:00): "The ...
5
votes
1answer
515 views

If the Moon had gravity as good as the Earth and a magnetic field could it have supported life?

If the Moon had gravity as good as Earth and a magnetic field could it have supported life? Because if the Moon had gravity, it could have retained water more than is present today on the surface. ...
5
votes
4answers
1k views

Why do we weigh less when falling?

I don't want to go to science world to find out because it would be a long round-trip. I understand that acceleration/deceleration would effect the weight and I can also imagine that someone at ...
6
votes
1answer
274 views

Does conformal gravity explain the Bullet cluster lensing effects?

Conformal gravity is an "alternative" theory of gravity, where instead of using the Einstein-Hilbert action composed of the Ricci scalar, the square of the conformal Weyl tensor is used. It was ...
2
votes
2answers
1k views

Is time speeding up due to the expansion of space?

If we just look at our local galactic cluster, if all of the galaxies that are a part of it are moving away from each other, and so the overall 'density' of the strength of gravity in the cluster is ...
-3
votes
1answer
123 views

Lightest flying solid material [closed]

I need to use a number of lanterns, to write something with it! I would like to use a light material which will bind the lanterns together (separated by space) so it looks like dotted letter. I know ...
4
votes
3answers
215 views

Is there a mathematical relationship here or am I looking for relations when there are none?

When I was taking classical mechanics, we dealt a lot with pendulums, and orbiting bodies problems. This lead me to think about the two situations depicted above. Left: Shows two balls of equal mass ...
2
votes
1answer
172 views

Vertical Load Reactions On A Ramp

Hello, I'm working on a small hardware project. I have two load sensors located at distance $S_1$ ($x=0$) and $S_2$. Assuming we ignore the weight of the ramp ... What is the load on $S_1$ and ...
2
votes
2answers
188 views

Photons and Relativity

Consider a Photon from Sun and travels with a velocity $c$. Now think we are that photon. For us, it looks like Sun is moving away from us with a velocity $c$. So, why don't we get attracted back ...
3
votes
2answers
372 views

Deviation from Earth's orbit

How much orbital deviation is required for the Earth to get knocked out from current orbit so it either moves away from Sun or towards the Sun?
10
votes
3answers
1k views

What is the exact gravitational force between two masses including relativistic effects?

I was wondering if there is a closed-form formula for the force between two masses $m_1$ and $m_2$ if relativistic effects are included. My understanding is that the classic formula $G \frac{m_1 ...
4
votes
2answers
184 views

Is Brian Cox right to claim that Gravity is a strong force for large masses, is it wrong, or is it only a matter of interpretation?

I watched a program of his in which it was claimed that since mass bends space in accordance to General Relativity, then in the case of very large stars it becomes a strong force to the point of being ...
0
votes
3answers
701 views

Aircraft Level Flight Trajectory

An aircraft climbs to 15000 feet and enters 'level flight' phase. My basic knowledge of physics says that forces on the aircraft at this time are balanced - as seen in this diagram. ...
2
votes
1answer
111 views

Conservative forces intuition

Take a gravitational field (with all the field lines pointing inwards) and a perfectly circular curve as an object's trajectory. To find the work exerted by the force on the object, compute the line ...
0
votes
1answer
162 views

Would an object hit the ground faster when it gets launched vertically upwards or downwards?

A while ago I had a discussion with someone about the speed of an object when it hits the ground. When does an object hit the ground faster: When you launch the object to the sky so it can fall ...
3
votes
2answers
300 views

Bowling ball on a rubber sheet

After reading a layman's guide to general relativity, I began to wonder what shape a bowling ball on a large rubber sheet would produce. For simplicity, I would like to assume that Hooke's law applies ...
4
votes
2answers
211 views

In a spaceship, if a vessel suddently stops will an object inside the vessel keep going?

My question is a 2 part question. First if a vessel in space is going very fast and suddently stops (maybe it is not possible but that is not the point) will things/humans inside the vessel keep ...
2
votes
2answers
215 views

Gravitation force- Attraction and repulsion

Gravitation force is always attractive. Now assume(not a practical one): I took our Earth in my hand and started shaking up and down. This will create a disturbance in space-time warp and it moves ...
10
votes
2answers
656 views

What is the weight equation through general relativity?

The gravitational force on your body, called your weight, pushes you down onto the floor. $$W=mg$$ So, what is the weight equation through general relativity?
0
votes
1answer
117 views

How could the relative zero gravity of the International Space Station be canceled? [duplicate]

Possible Duplicate: Will a machine or a technique ever be possible that allows gravity in space? I'm wondering how it would be possible for science to cancel out the experience of zero ...
2
votes
3answers
542 views

If everything in the universe doubled in size overnight, would it be noticeable?

By my understanding, if everything doubled in size, such as the Sun and the Earth, and because the space in between them (which is nothing) can't expand, would the gravities greatly change and the ...
14
votes
3answers
804 views

Why don't I feel pressure on my body when swimming under water?

If I put a couple of lead bricks on my foot, there would be a definite sensation of a heavy, perhaps even painful, force. Calculating the pressure for $20 kg$ of lead over a $100 cm^2$ area of my ...
2
votes
2answers
154 views

CERN projects on gravity

Recently I was reading about CERN's upgrade to work on gravitational theories. But if most of the work has been done by General Theory of Relativity than with other theories are there that need to be ...
4
votes
1answer
630 views

Planetary Gravity and its effects

This is my first question on the Physics portion of Stack Exchange. I was hoping to get some light on the topic of gravity. I don't have much background knowledge of physics so I might as well start ...
29
votes
6answers
1k views

Can I survive a free fall using a ramp and a rope?

Can I survive a free fall by carrying a very light and resistant ramp using a rope? Note: lets assume the ramp is a little bit heavier at the bottom and I am very skilled at making it always land ...
7
votes
3answers
458 views

Tidal force on far side

I have a question about tidal forces on the far side of a body experiencing gravitational attraction from another body. Let's assume we have two spherical bodies $A$ and $B$ whose centers are $D$ ...
4
votes
2answers
230 views

Is this closed time-like curve in a Godel universe a “circle”?

Would the observer moving along the circle in this Godel space-time diagram feel fictitious forces as though he is accelerating along a circular path or would he simply arrive at an earlier point in ...
0
votes
1answer
243 views

Software to simulate dynamics of objects in a given gravitation field [closed]

I want to simulate and test set of 2D designs that basically have pulley/gear/chain-linked systems under Gravity (For e.g. to check how a pulley would rotate given particular weights, of course I'm ...
19
votes
1answer
359 views

Flames with no gravity?

I was watching "Solaris" (Tarkovsky) today, and noticed this: in some moment the space station changed orbit and the people inside experienced zero-gravity. At that moment, a candlestick passed ...
3
votes
0answers
48 views

Attractiveness of spin 2 gauge theories [duplicate]

Possible Duplicate: Why is gravitation force always attractive? I have heard that the attractiveness of gravitation is due to the fact that it is a spin 2 gauge theory. Why is this so? I ...
7
votes
1answer
172 views

Materials with different gravitomagnetic permeability?

If you start with general relativity, and assume small perturbations around a nearly flat metric, it is possible to obtain linearized equations of gravity that look a lot like Maxwell's equations, ...
-4
votes
2answers
108 views

super-jump air balloon [closed]

We have the following objects: a 80 kg person a rope of negligible weight a balloon filled with helium, which can lift for around the same weight, 80kg. My question is, which of the following ...
8
votes
2answers
394 views

Wavefunction collapse and gravity

If gravity can be thought of as both a wave (the gravitational wave, as predicted to exist by Albert Einstein and certain calculations) and a particle (the graviton), would it make sense to apply ...
2
votes
6answers
2k views

Do you feel gravity?

I have been reading a few articles about the question why we don't feel/notice gravity in everyday life, but I couldn't understand why exactly we don't feel/notice it, that is, why we don't feel a ...
0
votes
1answer
126 views

Nothing escapes BHs, gravitons mediate gravity, so why do BHs gravitate? [duplicate]

Possible Duplicate: How does gravity escape a black hole? Nothing escapes black holes, gravitons mediate gravity, so why do black holes gravitate? My question is, "where is the hole (no ...
3
votes
3answers
356 views

What kind of energy gravitates, and why?

When listing energies for the purposes of keeping track of conservation, or when writing down a Laplacian for a given system, we blithely intermix mass-energy, kinetic energy and potential energy; ...
0
votes
0answers
355 views

What is the pressure in a vertical pipe that has moving fluid through it?

I have a system like this When the valve is closed, pressure along any point along the thin tube may be found thru pgh. 1. What about when the valve is opened? 2. Does the top of the jar need to be ...
6
votes
0answers
265 views

Alcubierre warp bubble effect on gravity and space

I read the question Faster-than-light communication using Alcubierre warp drive metric around a single qubit?, and these questions came to mind: What kind of impact would an Alcubierre warp bubble ...
2
votes
0answers
163 views

What is the critical mass of a planet to have an atmosphere like Earth's?

Small planets/orbits like Moon cannot have atmosphere because of their masses. They don't have enough gravity to hold an atmosphere. Then what is the critical mass that makes enough gravity to keep an ...