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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1answer
934 views

What is the longest distance that can be jumped after swinging from a rope?

In the movie Mission Impossible 3, the main character Ethan Hunt tries to enter a building in Shanghai by swing through the sky, as shown below: The jump consists of 2 sections, the red part, which ...
4
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2answers
1k views

What do you feel when crossing the event horizon?

I have heard the claim over and over that you won't feel anything when crossing the event horizon as the curvature is not very large. But the fundamental fact remains that information cannot pass ...
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3answers
5k views

If the earth would stop spinning, what would happen?

What would happen if the earth would stop spinning? How much heavier would we be? I mean absolutely stop spinning. How much does the centrifugal force affect us? If you give technical answers (please ...
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3answers
2k views

Why doesn't a fly fall off the wall?

Pretty simple question, but not an obvious answer at least not to me. I mean you can't just place a dead fly on the wall and expect it to stay there, he will fall off due to gravity. At first I ...
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5answers
3k views

Where does the “g” force that pilots experience come from?

I understand that it has to do with acceleration. Say a pilot does a quick maneuver and experiences a force of 5g. What exactly is happening here? And what is this force relative to? If someone ...
4
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1answer
502 views

Could this fountain, under the right conditions, technically be able to lift me up?

There is a big fountain in a lake in my city. I was talking with a friend and we were wondering whether it would be able to lift me up. I sent a few emails and obtained information about the ...
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3answers
267 views

What will be the shape states of water in a centrifuge in 0G

Consider the concept of these videos http://www.youtube.com/watch?v=Zip9ft1PgV0&sns=em and http://www.youtube.com/watch?v=cUhgKFV5Ri4&sns=em but set in a zero gravity environment and in a ...
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1answer
687 views

What gives matter Gravitational Mass? [duplicate]

Possible Duplicate: Does the equivalence between inertial and gravitational mass imply anything about the Higgs mechanism? In Higgs mechanism, Higgs field, which likes syrup, slows down ...
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2answers
1k views

Lever Mechanics - How to formulate an ideal lever launch

Let's say I have a simple lever as shown below, and the lever is massless and the pivot is frictionless and there is no air resistance. I'm thinking the cradle for the projectile would have to have a ...
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3answers
179 views

How to incorporate effects of gravity in a many-electron system?

In the weak interaction limit, behaviors of electrons can still be described by a 1-partitcle equation with a modified mass, where the change in mass can be understood as effects of other neighboring ...
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2answers
166 views

Why is the critical density of the Universe non-zero?

I'm missing something and I wondered if someone could enlighten me. As I understand it, Einstein's equations say, among other things, that matter curves spacetime. I also understand, the Universe has ...
0
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1answer
116 views

picture of newtonian gravity and black hole

We assume that the earth planet is a black hole. When a light beam is fired. The only way that even light can move is A and B which means this is impossible that light move on other ways C, D, E ...
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1answer
323 views

detect movement - how does it relate to G force

I would like to detect if a user is moving by using an android smartphone - walking or jumping doesn't matter - want to know if the user wearing the smartphone is moving. I have found this code ...
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1answer
544 views

Space Rocket Lift Efficiency and the Gyroscope?

I'm no physicist apart from basic 3d web animation, I'm just curious and please feel free to correct my misuse of terms or inadequate speculations. I've been reading a lot on gyroscopes and ...
4
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1answer
236 views

Is the fuel burn for a satellite launch affected by the position of the moon relative to the launch site?

The gross mass of a satellite rocket is tiny compared to that of Earth, and Luna. Between them, however, the two bodies set up tides in bodies of water which itself is again considerable mass. At ...
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4answers
2k views

Could we make a trebuchet that could launch objects to a stable orbit?

Inspired by this xkcd, which calculated the energy requirements for accelerating individual humans to escape velocity (regardless of consideration for what that would do to your organs), I am ...
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6answers
3k views

Why is there an escape velocity?

I've been trying for days, but I just can't understand why escape velocities exist. I've searched the web and even this site, and although I've read many explanations, I haven't been able to truly ...
1
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1answer
501 views

Why a black hole sucks nearly everything, but emits gravitons?

What is so inherently different to the idea of gravitons from other particles, that a black hole draws everything possible including massless photons, but emits gravitons the more the stronger it ...
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2answers
160 views

Has anyone ever actually compared the weight of a heavily loaded centrifuge when it is spinning and not spinning?

I have searched the internet and have not found any actual test results.
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0answers
421 views

include the stretch of the spring own weight in potential energy for spring pendulum?

we are given a problem with spring with its own mass $m$. I am confused how to set up the PE term in the Lagrangian. Assume the spring has length of $L_{0}$ when it is laying on a table horizontally. ...
2
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2answers
263 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/ ...
7
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3answers
356 views

why there is no accuracy of the measured value of $G$?

With the advancement of Modern Technology still there is no accuracy of the measured value of $G$ Gravitational Constant, why!?
3
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2answers
302 views

Do black holes accelerate in spin as they obtain more mass?

It is known that - When a star collapses during the formation of the black hole, the black hole obtains the spin of the star which it collapsed from... What I'd like to know is, If this spin ...
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2answers
338 views

The physics behind The Great Flood [closed]

The book of Genesis floats (pardon the pun) some interesting numbers when discussing the Great Flood. For example, it rained for 40 days and 40 nights, and at the end of that time, the entire planet ...
3
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2answers
378 views

How to measure g using a metre stick and a ball

Can I measure the value of g using only a metre stick and a ball? I am not supposed to use a stopwatch and that has been the problem. NOTE: I do not know if a solution exists or not.
3
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1answer
347 views

LIGO Gravitational Waves [closed]

Has LIGO detected any gravity waves yet, or any hints of them? Is it just that LIGO is not sensitive enough or are we now entering disconfirmation territory? If we never detect gravity waves with any ...
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4answers
2k views

Black-holes are in which state of matter?

Wikipedia says, A black hole grows by absorbing everything nearby, during its life-cycle. By absorbing other stars, objects, and by merging with other black-holes, they could form supermassive ...
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1answer
1k views

Atmospheric escape of gas molecules

Most of the objects in space are likely to have an atmosphere. Since space is void, the gases in atmosphere should have either dissolved or emptied into space. But, some of the objects still seem to ...
2
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1answer
145 views

variations of Einstein equations with conversion between gravitational and non-gravitational energy

I'm looking for existing papers studying a variation to Einstein equation that does not rely on the annoying matter conservation identity: $$ T_{\mu \nu; \nu} = 0 $$ And instead tries to equate the ...
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3answers
278 views

If a star were to suddenly dissapear, would it still have gravity?

I am wondering whether or not literally anything can travel faster than the speed of light. For example, if gravity from a star immediately ceases to have an effect if it suddenly and magically ...
0
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1answer
310 views

Relation between Higgs boson and force of gravitation

I don't know and I can't handle it. I am so much curious about the recent discoveries in science. European Space Agency and NASA are doing great work. Hats up to these institutions. My nights are ...
2
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0answers
87 views

How can black holes have gravity? [duplicate]

Possible Duplicate: How does gravity escape a black hole? How can gravity get out of a black hole? If a black hole is so powerful that even light does not travel fast enough to get out, and ...
7
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2answers
3k views

Is anti-gravity possible in theoretical physics?

Is anti-gravity possible in string theory? I have read some articles about scientists making assumptions about the existence of anti-gravity, but is it possible in string theory?
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2answers
727 views

Consequences of destroying a space elevator

Suppose there is a fully functional space elevator built on Earth. The base is attached to coordinates $ (\lambda, \varphi) = (0,0) $ e.g., on the equator on the zero-meridian. What would happen ...
7
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3answers
26k views

How is light affected by gravity?

Light is clearly affected by gravity, just think about a black hole, but light supposedly has no mass and gravity only affects objects with mass. On the other hand, if light does have mass then ...
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1answer
315 views

Can an electric motor force angular momentum not to be conserved in an isolated system?

An ice skater is in a spin, she pulls her arms in and she spins faster, she lets her arms extend outward and then she starts to slow down. She will probably weigh on a weigh scale about the same ...
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2answers
2k views

What is the likelihood of ever discovering the graviton?

How would one look for and confirm existence of a graviton? Someone was speaking to me about perhaps one day discovering the graviton, but to me it seems unlikely, although I'm young and essentially ...
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2answers
105 views

What allows new born suns to travel away from each other?

What allows massive new born suns to move away from each other, as they have been observed. I would think that their massive gravity would prevent this and cause them to slam into each other.
7
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2answers
11k views

What is the escape velocity of a Black Hole?

The escape velocity of Earth is $v=\sqrt{\frac {2GM}{R}}$, where $M$ is the mass of the Earth and $R$ it's radius (approximating it as a sphere), and is much less than light speed $c$. But I want to ...
7
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6answers
3k views

Gravitation is not force?

Einstein said that gravity can be looked at as curvature in space- time and not as a force that is acting between bodies. (Actually what Einstein said was that gravity was curvature in space-time and ...
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5answers
607 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
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1answer
73 views

What is the shortest run needed for a “dropped skateboard” rider to reach 160 mph?

I just saw a great clip on the fastest skateboarder to date. He wants to reach 160 mph from a dropped board, but says his speed is limited by the roads currently available. What is the shortest run ...
2
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3answers
616 views

The theory of moon creation when a Mars size planet hit Earth

As we know the predominant theory where does the moon come from is that a Mars size planet hit the earth and took a chunk out of it which eventually materialized into moon. My question is that if a ...
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3answers
534 views

Can gravity be absent?

Can gravity be absent? Not weightlessness as an astronaut experiences it because the astronaut's body still has gravity which will probably manifest in the presence of another smaller/larger body. For ...
5
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3answers
791 views

Do rotating bodies emit gravitational waves?

Suppose we have a cylinder of mass $m$, radius $R$ and height $h$ in rotation with speed $\omega$ around its symmetry axis with no friction (ideal situation). I'd expect this cylinder to emit ...
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1answer
139 views

Are there still Big Bang Gravitational effects

If all matter was concentrated at one point before the big bang, I assume that the gravity was at a huge scale. For a long time many believed that the universe would eventually collapse back upon ...
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1answer
307 views

vector-scalar gravity

Has anyone developed a vector-scalar theory of gravity using an acceleration field equation that is based on a ratio in which the numerator is the familiar Newtonian vector sum of all masses times the ...
3
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1answer
69 views

Can extremely charged objects simulate some black hole effects?

If we had a positive point charge of incredible quantity, does there exist an imaginary sphere about it, such that regardless of the initial speed and direction of any electron, that electron could ...
3
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1answer
2k views

The trajectory of a projectile launched from a hilltop

Here is the problem: A boy stands at the peak of a hill which slopes downward uniformly at angle $\phi$. At what angle $\theta$ from the horizontal should he throw a rock so that it has the greatest ...
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2answers
2k views

Why is Gravitational force proportional to the masses?.

We know that two mass particles 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?