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by Ron Kurtus

A total of 64 comments and questions have been sent in on Gravitation. They are listed according to date.

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List of next 10 letters




Gravitation Gravitation on huge planet USA
Gravitation Relation between wormholes and gravitation India
Gravitation What is the origin of gravitation? India
Gravitation Energy from a gravity wheel Ireland
Gravitation Importance of time in a Black Hole India
Gravitation Interested in graviton theory USA
Gravitation How large does a star have to be to become a black hole? USA
Gravitation Relationship between dark matter and graviation? USA
Gravitation Who determined gravitation equation? UK
Gravitation Does dark matter cause people to be negative? RSA

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First 10 letters

Gravitation on huge planet

Topic: Gravitation


December 7, 2010

I was wondering if you could send me some equations for measuring the force of gravity that is possessed by an object of particular size. The reason being I had a dream where I saw a planet that was 1000 times bigger than our galaxy and I know that a planet that size isn't possible, but if it were, I wanted to know the force of its gravitational attraction, what a 50 kilogram person would weigh on it, and its escape velocity, and I don't remember the equations to calculate those. Could you please label what each variable in those equations are? I'm sort of new to physics.

Dylan - USA



The radius of the Milky Way galaxy is about 50,000 light years. That is about 5*10^20 m. Your planet would have the radius of 5*10^23 m (5 followed by 23 zeros).

The mass of the galaxy is 1.4*10^42 kg. However, it is not solid and has much empty space in it. However, if your planet was solid, it would collapse on itself and become a Black Hole.

Suppose the planet had 10^15 times the mass of the Milky Way = 1.4*10^57 kg.

Now F = GMm/R^2. If the person had a mass to 50 kg, the multiplication factor would be GM/R^2 =

(6.67*10^-11)(1.4*10^57)/(5*10^23)(5*10^23)= 0.37

In other words, the person would weigh about 1/3 of the weight on Earth. The reason is that even at 10^15 times the mass of the galaxy, the density is so small and the matter is so spread out that the weigh is not at great as you would expect.

This gives you an idea how to calculate things. For escape velocity, see:

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Relation between wormholes and gravitation

Topic: Gravitation


November 2, 2010

Is there any relation between wormhole or time travel with gravitation.and what are these ?

vijit - India



Time-travel and wormholes are considered possible in some physics and astronomical theories.

The General Theory of Relativity view of gravitation relates it to a curvature in space-time. This theory also allows the existence of wormholes, but they have never been experienced.

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What is the origin of gravitation?

Topic: Gravitation


October 31, 2010

Q origin of gravitation?

vijit - India



Gravitation is one of several properties of matter.

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Energy from a gravity wheel

Topic: Gravitation


June 20, 2010

subject energy from gravity wheel
A big wheel 40 ft. high= to 60 ft. half circle has 4 half ton weights constantlt grip on the down side all the time for 1 minute
what speed will it reach, and what energy or power if concected to a generator could it produce
thanking you for allowing me to ask

- Ireland



There is a lot of information missing, in order to draw any conclusions.

If the wheel is rolling down an incline, you need to know its coefficient of rolling friction, as well as the angle of the incline to determine its speed and power it will generate.

Also, an electrical generator requires a force to turn its rotors, depending on its size and configuration of its magnets.

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Importance of time in a Black Hole

Topic: Gravitation


June 15, 2010

in black hole concept what is importance of time

sam - India



A Black Hole is an object that has such high gravitation that light cannot escape. According to the Theory of Relativity, in extreme conditions like this, space is greatly distorted, as is time.

Of course, it is impossible to prove that time is distorted in a black hole, because there is no real way to measure it.

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Interested in graviton theory

Topic: Gravitation


June 10, 2010

"Recently it has been pointed out that the characteristic quantum-gravity scale could be as low as the weak scale in theories with gravity propagating in higher dimensions. The observed smallness of Newton's constant is a consequence of the large compactified volume of the extra dimensions. We investigate the consequences of this supposition for high-energy collider experiments. We do this by first compactifying the higher dimensional theory and constructing a 3+1-dimensional low-energy effective field theory of the graviton Kaluza-Klein excitations and their interactions with ordinary matter. We then consider graviton production processes, and select photon plus missing energy and jet plus missing energy signatures for careful study. We find that both a 1 TeV e+e- collider and the CERN LHC will be able to reliably and perturbatively probe the fundamental gravity scale up to several TeV, with the precise value depending on the number of extra dimensions. Similarly, searches at LEP2 and the Tevatron are able to probe this scale up to approximately 1 TeV. We also discuss virtual graviton exchange, which induces local dimension-eight operators associated with the square of the energy-momentum tensor. We estimate the size of such operators and study their effects on two fermions to two photons observables." Gian F. Giudice, Riccardo Rattazzi, James D. Wells
Journal reference: Nucl.Phys. B544 (1999) 3-38
DOI: 10.1016/S0550-3213(99)00044-9
Cite as: arXiv:hep-ph/9811291v2

A few questions on this:
1. The graviton theory represents gravity as a particle, a particle has mass. Thus wouldn't gravity then act upon itself? Any detection of a graviton and its propagation would hide the base field acting on the graviton itself. With the graviton propagating in at least 8 dimensions would the gravitational affect of those 8 dimensions create a graviton in any remaining dimensions giving rise to quantum gravitons?
2. Quantum is a 'state' that is undetermined until it is observed. Does a 'quantum particle' exhibit gravity? How do you know? Once you observe the gravity are you not also observing the particle making it no longer "quantum"?
3. Is there an established base value of gravitational length like "Planck Length"? What is that value called and how is it conceived?
4. Will the detectors in the LHC be able to detect initial gravitational lengths?
5. What is low scale quantum gravity and what is the factors that define the TeV scale?

Thank You.

tom - USA



Particles such as the graviton and photon have zero REST mass, as opposed to a particle like a proton, which has a specific mass when at or near zero velocity.

Although a photon has zero rest mass, light does exhibit momentum and can apply a force, such as seen in solar sails. I don't know about the graviton, although a similar principle may apply. However, while solar pressure can push on object, gravitation is a pulling force. The explanation of gravitation, using a graviton involves some sort of exchange of particles.

Quantum is not a state. Rather, particles can be in various quantum states.

String theory and a few other theories mathematically consider multiple dimensions. However, just because something is mathematically correct does not mean that it truly exists in the physical world. These theories can neither be proven or disproven.

The article you provided it is interesting, but it is beyond the scope of our material.

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How large does a star have to be to become a black hole?

Topic: Gravitation


May 27, 2010

How large does a star have to be to become a black hole? is it possible for anything to escape a black hole? What would the mass of an object have to be to escape a black hole?




There is a point a star's lifetime where it cools enough that it will collapse on itself. A black hole the mass of the Sun would only be 3 km in diameter.


Although it is called a black hole because nothing is supposed to escape, not even light, particles and light does escape from its poles, due to its internal rotation.

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Relationship between dark matter and graviation?

Topic: Gravitation


May 12, 2010

What is the relationship between dark matter and graviational force? ....Is dark energy the "reminent energy" from the big bang?

michael - USA



The existence of dark matter is really speculation, as an effort to explain the motion of some stars. The motion could be caused by an extension of Relativity or by some of the laws of motion being different in various parts of the Universe.

The same is true of dark energy. It could be a form of anti-gravity, perhaps from dark matter, or it could be some other phenomenon.

The properties of matter and gravitational force seem to change with size and velocity. At the quantum level, there are certain rules. At the everyday level, Newton's laws hold. Then at the astronomical level and high velocities, relativity comes into play. Perhaps dark energy and dark matter are extensions at the extreme end, beyond relativity's influence.

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Who determined gravitation equation?

Topic: Gravitation


March 9, 2010








Isaac Newton formulated the equation F = GMm/R^2 in the UK in 1687. However, British scientist Robert Hooke claimed Newton got the equation from him.

They both were involved in the Royal Society. I don't think they have any formal names for their laboratories or if they even had labs.

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Does dark matter cause people to be negative?

Topic: Gravitation


October 27, 2009

Is it because of the size of dark matter in the Universe that the way people think consciously is so negative.Does dark matter influance our ability to think and in which way.Is it dark matter in modern day that puts people under pressure.Is dark matter more advantages to modern human beings than cosmic light.Does cosmic light and dark matter work together.

Marius - RSA



Dark matter is called that because it does not seem to give off light or reflect light. Since no scientists have seen it they call it "dark" matter.

But there seems to be some dark influence of people these days. Many seemed to be thinking so negatively, complaining above others, and just being plain mean. Some of it has to do with the fact that the news media emphasizes bad things. If you look around yourself, I think you'll see that most of the people that you know are actually very positive. It is like some cosmic light shining on them.

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