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Feedback Comments on Gravitation

by Ron Kurtus

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

You can read them to further your understanding of the subject.



List of next 10 letters

Topic

Title

Country

Gravitational Escape Velocity with Saturn V Rocket Why are stages needed in a rocket? Australia
 
Gravitation Gravitational dipole radiation Sweden
 
Gravitation Gravitation and curved space UK
 
Gravitation How are black holes detected? India
 
Gravitation Device that affects graviton particles USA
 
Gravitation Universal Gravitational Constant in a Black Hole India
 
Gravitation How do you measure something faster than light? Serbia
 
Gravitation Equivalence of gravitation USA
 
Gravitation Does escape velocity depend on direction? Nigeria
 
Gravitation When a rocket blasts toward the Sun USA
 

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First 10 letters


Why are stages needed in a rocket?

Topic: Gravitational Escape Velocity with Saturn V Rocket

Question

September 26, 2012

Thanks for this Kurt. Here is a question for you (let's ignore atmospheric resistance). I understand that escape vel is the velocity at which a projectile could be projected from a point in the earths grav field so that it will not return to earth. I assume that with rockets, once escape vel is attained, engines can be turned off but the rocket will still escape the earth. Does this mean that as long as the engine is "kept running" the rocket can escape the earth travelling at a vel considerably less than escape velocity? Also, if this is so, why is staging necessary? Kind regards and thanks for your website.

Tom - Australia

22959

Answer

As long as the engines continue, a rocket does not have to reach the escape velocity to escape the Earth's gravitational pull.

The reason for having stages in a rocket is to get rid of extra weight, once the fuel in a stage is spent.

I'm glad you find the material useful and interesting.

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Gravitational dipole radiation

Topic: Gravitation

Question

December 10, 2011

I have been working on the subject of gravitation for many years. My results are shown on my Gravitation homepage.

The crucial matter seems to be gravitational dipole radiation. If you accept this phenominon you end up with a result capable of explaining boath dark matter and dark energy.
Yours sincerely

Boris - Sweden

22262

Answer

Although electrical and magnetic forces are dipole in that they require opposite poles, most theories say that gravitational forces are monopole. However, there are indications that gravitation may also be dipole in some form.

A good article on the subject is Gravitational Dipole (PDF).

In your page, you mention the exchange of energy between matter and ether. Although the theory that space is made of ether is considered obsolete, I feel it still has some possibilities.

Best wishes in your continued study of gravitation.

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Gravitation and curved space

Topic: Gravitation

Question

November 3, 2011

IF MASS IS EQUIVALENT TO ENERGY FROM E=MCSQUARED - THE N THE EARTH FOR EXAMPLE WE WOULD EXPECT TO DEVELOPE A REDUCING ENERGY GRADIENT THROUGH AMBIENT SPACE.IN FACT IT DOES ACC TO THE LAW OF UG - THIS EXPLAINATION FOR THE CAUSE OF GRAVITATION SEEMS TO SATISFY ME.HOWEVER I HAVE NOT SEEN IT GENERALLY EXPRESSED IN TEXTBOOKS. THE GENERAL RELATIVITY THEORY OF GRAVITATION IS SO PROFOUND I BELIEVE THAT DIRAC ONCE SAID IF IT HADNT BEEN FOR EINSTEIN WE WOULD NEVER HAVE COME TO IT. WHEN PHYSICISTS TALK OF MATTER CURVING SPACE DOES THIS MEAN THE EFFECT OF THE EARTHS REDUCING ENERGY GRADIENT-OR IS IT MORE PROFOUND.

BILL - UK

22133

Answer

If the mass "m" was changed to electromagnetic radiation, its energy would be E = mc^2. Einstein certainly was instrumental is establishing the General Relativity Theory of Gravitation. Others had worked on it, but he was the one who put the concept together.

Space seems to be much more than where no matter exists. Space has properties, and one of them is its geometry is affected by matter, such that the lines of space curve toward objects of mass.

For an overview, see General Relativity Theory of Gravitation.

I'm not sure what you mean by the Earth's energy gradient.

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How are black holes detected?

Topic: Gravitation

Question

August 13, 2011

I answered 3 questions out of that 2 was right,I ma really interested in studing black holes and I want to ask one thing how black holes are detected through space it is said that no light can escape through it

George - India

21887

Answer

When astronomers observe stars over a period of time, they may see some of them vanish when they pass by a certain point in space. A reason the star seems to vanish is because there is a black hole in between the star and the Earth.

The black hole does not give off light, and it also blocks or absorbs light coming from another object.

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Device that affects graviton particles

Topic: Gravitation

Question

August 12, 2011

I have a question, What if I told you that I think I figured out how to combine a magnetic field with a gravitational field, by understanding how matter exchanges graviton particles, I have a idea for a device, If I put it together,, Would it be dangerous,, I do not want to take chances.

Nick - USA

21886

Answer

A strong gravitational field can distort a magnetic field. The opposite may also be true.

If you have a device that can measure the exchange of gravitons or affect them with a magnetic field, I doubt that it would be dangerous. The biggest problem is in verifying the effect you are trying to do.

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Universal Gravitational Constant in a Black Hole

Topic: Gravitation

Question

July 13, 2011

what is the value of universal gravitational constant on black hole ?

- India

21809

Answer

The Universal Gravitational Constant is a proportionality factor for the force between two masses at some distance. The value has been determined experimentally.

At quantum sizes and distances, the value of the Gravitational Constant is no longer constant. However it has not been accurately measured.

Likewise, in the extreme case of inside a Black Hole, the Constant also fails. Unfortunately, its value or variation has not been determined.

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How do you measure something faster than light?

Topic: Gravitation

Question

June 29, 2011

Hello.
How do you measure if something is faster than light?

Despot - Serbia

21776

Answer

According to the Theory of Relativity, no objects or waves can travel faster than light. To measure the speed of something, you need to know the distance traveled and then measure the time it takes to go that distance.

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Equivalence of gravitation

Topic: Gravitation

Question

June 28, 2011

Einstein demonstrated that a gravitational (stationary environment) and acceleration (motion) are equivalent. But since the corresponding velocities and displacements for the gravity and acceleration environs are not the same is it still OK to conclude that gravity and acceleration are equivalent?

John - USA

21773

Answer

This is known as the Strong Equivalence Principle or the Einstein Equivalence Principle. A brief explanation is seen at Equivalence Principles of Gravitation

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Does escape velocity depend on direction?

Topic: Gravitation

Question

April 8, 2011

You say that the escape velocity doesn't depend on direction; but if an object is projected at an angle other than normally to the earth surface I suppose that it should travel a less radial distance from the earth's center for the same launch velocity; and so I assume that the direction may be relevant to an object trying to reach infinity (speaking strictly theoretically)and hence the (escape)velocity at which it is launched. I would really appreciate an elucidation of why it is escape speed (strictly speaking) and not velocity.
Thank you

- Nigeria

21456

Answer

Escape velocity can occur for an object projected vertical or normal to the Earth's surface or at other angles up to being tangent to the surface. At the tangent angle (90 degree from the vertical), the object will travel in a parabola which extends to infinity, provided the velocity is great enough.

At greater angles than 90 degrees from the vertical, the object will probably strike the Earth's surface, preventing it from going into space.

Some sources call it escape speed and say that any direction is possible. However, since there are limitations on the projected angles, I prefer to consider it escape velocity, especially since you can define the exact direction that you are projecting the object.

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When a rocket blasts toward the Sun

Topic: Gravitation

Question

January 30, 2011

As it pertains to escape velocity from earth with the sun's influence, if the equation and numbers are correct, if a rocket blasts off directly toward the sun, then the sun would pull the rocket off of the earth and accelerate it away since the Sun's Ve was about twice that of Earth's. Am I reading that right?

Mike - USA

21115

Answer

The derivation of the escape velocity requires the object or rocket to start at an initial velocity and move away from the gravitational force, slowing down, until it reached the hypothetical infinite distance.

However, when the rocket escapes the Earth and moves toward the Sun, the gravitational attraction of the Sun increases the rocket's speed until it crashes into the Sun. The escape velocity equation does not work in that situation, since the external force from the Sun is influencing and increasing the rocket's velocity.

The situation would require combining the opposing forces from the Earth and the Sun on the rocket.

Since you brought this up, I will add a clarification about this situation in the lesson.

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