by Ron Kurtus

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

## List of next 10 letters

### Country

Gravitation I want to explore the effects of universal gravity India

Gravitation Velocity Radius of Black Hole seems incorrect USA

Gravitation Object falling down tube through center of the Earth USA

Gravitation Gravitation with liquid between two objects India

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First 10 letters

## I want to explore the effects of universal gravity

Topic: Gravitation

### Question

October 23, 2009

Hello!

I want to explore the effects of universal/absolute gravity, meaning the effect of gravity of a body on the same body.

Would you like to indulge?

Shahin

- India

18565

Every atom in an object or body attracts the other atoms due to gravitation. This was a force that was instrumental in the formation of the various stars and other objects in the universe. At close distances of atoms, electrical attraction supersedes gravitational attraction.

Is this what you are referring to?

## Radius of Black Hole seems incorrect

Topic: Gravitation Velocity

### Question

October 6, 2009

On the page "Gravitational Escape Speed" just before the Summary, you have the radius of the Black Hole with Mass of our Sun calculated. In this calculation, the value of "2" is reintroduced into the calculation. Is this value not already taken into consideration when the R
Thank you,

Greg - USA

18448

You had me worried for a minute that I made a mistake. No, the 2 is supposed to be there.

R < M*1.5*10^?30 km

If you look several paragraphs above, you will see the mass of the Sun is about 2*10^30 kg.

Thus R < (2*10^30)*(1.5*10^?30) km = 3 km

## Object falling down tube through center of the Earth

Topic: Gravitation

### Question

September 21, 2009

Hello,
Thank you for your time and consideration. I have been thinking about gravity for a while and I am at some problems that I need help with because of lack of a lab. These can be thought of theoretical and I have some up with different conclusions.
1) Newton says that forces are equal and opposite each other. He also calls gravity a force. So if we could set up a two objects that are in a frictionless zone. Object one (Oi) is one gram, and object two (Oii) is two grams.
Now lets say that we could fix Oii in a location and let Oi "fall" to it. We could measure the time and speed Oi takes and has as it reaches Oii due to the force of gravity.
Now, lets set them up in the same zone and at the same distance but have Oi fixed to a point and release Oii. This is where i get confused. Newton would say that the force is the same so the Oii would reach the same speed as Oi had reached. But because force is accelerating objects, the object has twice as much inertia and should take more time to reach contact and also should not reach the same speed. Even though it is in a frictionless zone inertia still plays a part, right? If so I have more to say about this. But I don't want to get ahead of myself.
2) Lets say that the earth is perfectly and equally round.
Now we have some how made a tube that we stuck directly through the center of it. Now, we drop a perfectly round bowling ball with no holes into it. I want to say that the ball would stop in the center of the world. But the idea is that, How are you being pulled of forced by gravity if you are at the center of that object? This makes me think that gravity is not an attraction to a single source. It is an attraction to an infinite amount of objects. Think of how shapes are attracted to each other. A solid ball and a solid ball touch at one point. A square and a square touch on a plane. But a rubber ball touches a square at a depressed point, whereas the center is depressed the most and the edges of contact are depressed the least.
I have more but this is my first time writing you. Please contact me soon, to talk about these issues or explain them to me.

Stuart - USA

18359

The force of gravitation will cause two objects in space or any friction less zone to be attracted towards each other until they meet at the center of mass between the two. The force on one object is dependent on the mass of the other, according to Newton's Universal Gravitation Equation. See:
http://www.school-for-champions.com/science/gravitation_universal_equation.htm

If you dropped an object down a tube that passes through the center of the earth to the other side, it would result in the object reaching the center at some velocity and continuing on but slowing down until it reached the other side. At that time, it would reverse directions, pass through the center again, and move on to the original starting point. The object would continue oscillating back and forth between the two points. Of course, this is assuming there is no air resistance or friction on the object.

## Gravitation with liquid between two objects

Topic: Gravitation

### Question

August 27, 2009

does the gravitational force between two bodies change if they are placed in a liquid of certain density than that in vacuum?

dhruba - India

18218

The gravitational force between two objects is extremely small unless they are very large. Placing the objects in a liquid adds another factor, because the liquid is also matter and is attracted to both objects and its existence would add the the force.

Consider inserting another object in between two objects. For example, when the Moon is between the Earth and the Sun. In such a case, the pull from both the Moon and the Sun on the tides is greatest because the force of gravitation adds both components.

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