Calculate Gravity of 3 kg Rock in Vacuum

[qasrimoe]

i have a question how would you calculate the gravitational force of an object by it self in a perfect vacuum with no other forces applied to it . let s say the object is a 3 kg rock just siting in an empty space .

 

[mburt]

Is this object in space? If this is on earth, friction and Earth's gravity would overcome this gravitational force...

Keep in mind the Earth is an object with a diameter of 12 800 km. If an object is sitting on the ground, it's gravitational force must overcome that initial force (to have any real attraction).

however the formula for universal gravitation is (Newton's law):

Fg = G((m1m2)/d^2)

where G is the constant: 6.67 x 10-11 N m^2/kg^2.

m1,m2 are masses, and d is diameter

So yes, you would need another object to compare to get a gravitational force

 

[qasrimoe]

this object is in space by it self in space no forceses applied to it what so ever can we calculate it s garvitational force just by it s mass an diameter . thank you

 

[artikk]

Like the other poster had said, you would need a second mass to calculate the gravitational force exerted by the first mass using Newton's gravitational force equation. In the case of general relativity as it concerns gravity, I don't think it requires a second mass. So, using general relativity, you would be able to calculate the gravitational field(spatial distortion) of the mass in question. I'm not proficient at all with the theory though so I can't say much more than this.

 

[Creator]

this object is in space by it self in space no forceses applied to it what so ever can we calculate it s garvitational force just by it s mass an diameter . thank you

Simple...
Standard gravitational acceleration formula:

g = Gm/R^2

 

[artikk]

Simple...
Standard gravitational acceleration formula:

g = Gm/R^2

Doesn't that formula imply a second body though? Usually, the R and m would be that of the Earth, not the mass in question.

 

[qasrimoe]

thank you ,

 

[Creator]

Doesn't that formula imply a second body though? Usually, the R and m would be that of the Earth, not the mass in question.

Of course it does; how can you have a force on something that isn't there ? Duh?

..

 

[qasrimoe]

the force of the body is appliad to the body it sellf

 

[qasrimoe]

i call it self gravity

 

[qasrimoe]

...:)

 

[qasrimoe]

consider the Earth in space and some how it endded up with no planets around it it still going to have a gravitational force any way it hase a mass = it has a gravitational force

 

[artikk]

i call it self gravity

Are you serious? That's impossible, I think. No mass can exert gravity on itself, just on other objects-it's fundamentally an attractive force. For a 3 kg mass, using just mechanics , any force that is exerted by this mass is exerted on the environment around the mass, not on the mass itself. A small correction would be that if you consider the first mass a collection of small masses that comprise the larger mass, then each small mass would exert a force on the other smaller masses. But I am beginning to diverge from the original problem. Anyway, if a second mass was nearby, the first mass would exert a grav. force on the second mass since that's considered part of the environment of the first mass. In turn, the second mass would exert an equal and opposite gravitational force on the first force. It's an action reaction pair of forces.

 

[artikk]

consider the Earth in space and some how it endded up with no planets around it it still going to have a gravitational force any way it hase a mass = it has a gravitational force

I think it would really have a gravitational field. Meaning any mass that comes in close contact with the planet, would experience gravitational attraction from the planet. However, a field is not a force. At this point, I think I better let a more eloquent physics poster explain how gravity works.

 

[Dale]

Are you asking for the pressure at the center of a self-gravitating sphere? Or are you asking about the weight of a unit mass of the surface material, or what? You need to be a little more clear about what force you want to measure where.

 

[qasrimoe]

i got the ansewar for my question alerady thanks you

 

[Dale]

So, out of curiosity, what was the question and what was the answer?

 

[qasrimoe]

Are you serious? That's impossible, I think. No mass can exert gravity on itself, just on other objects-it's fundamentally an attractive force. For a 3 kg mass, using just mechanics , any force that is exerted by this mass is exerted on the environment around the mass, not on the mass itself. A small correction would be that if you consider the first mass a collection of small masses that comprise the larger mass, then each small mass would exert a force on the other smaller masses. But I am beginning to diverge from the original problem. Anyway, if a second mass was nearby, the first mass would exert a grav. force on the second mass since that's considered part of the environment of the first mass. In turn, the second mass would exert an equal and opposite gravitational force on the first force. It's an action reaction pair of forces.

why not i think that s what makes matter have mass in the first place ; this just an idia proving it is some thing else

 

[qasrimoe]

the question now is can mass exert gravity on itself?

 

[artikk]

http://en.wikipedia.org/wiki/Star

 

[qasrimoe]

yes but that s a colection of masses like you said earlier .
but in the other other hand every thing no matter how small it is is a colection of masses

 

[Dale]

Again, what was the answer to your previous question?

 

[qasrimoe]

the only way to prove it is to find a thing made of one particlee

 

[qasrimoe]

g=gm/r^2

 

[Dale]

g=gm/r^2

That is not a force, but if you really wanted the gravitational field instead of the force then I am glad you got your answer.

 

[qasrimoe]

gravitational field apllyes force to other objectes ? so can find the force that way i think ?

 

[qasrimoe]

i have some questions in onother thread about BEC if you can discusse it with me that will be nice

 

[qasrimoe]

That is not a force, but if you really wanted the gravitational field instead of the force then I am glad you got your answer.

i have some questions in onother thread about BEC if you can discusse it with me that will be nice

 

[Dale]

My knowledge of BEC is superficial. I would not want to contribute my necessarily ignorant comments.

 

[qasrimoe]

My knowledge of BEC is superficial. I would not want to contribute my necessarily ignorant comments.

mine as well but it does not hurt to exchange idias ; the scall of knowledge does not go down no matter how little you know about something it only goes up :)