jupiter

[blackeyed]

Why does jupiter has a high gravity?

[Teddio]

The surface gravitational field strength of a planet is a function of its mass and its diameter.

[blackeyed]

sorry for the late answer, it takes me a while to register the facts.
I am a little confused here i got that gravity depends on the diameter(or radius) and what?
density or mass???
I would say it's density and let me know if i am right.
And one more thing isn't gravity due to nuclear fission taking place inside a planet?

[blackeyed]

thought i heard about nuclear fission on nat geo, i will sure get it checked.
and is it mass or density?

[mibn2cweus]

Planets that have unstable elements, heavier than iron, typically have some fission reactions taking place but not of the intensity of nuclear reactors or bombs because the fission material is not sufficiently concentrated for a controlled or sustained chain reaction. Nor do planets have sufficiently concentrated mass to produce the fusion reaction of stars. Stars have large gravitationally concentrated masses sufficient to produce the pressure and heat required to initiate and sustain a fusion reaction.

All material objects are gravitationally attracted to each other but gravity is a weak force which only becomes readily apparent with large concentrations of matter. For spherical objects with equally distributed mass (uniform density), the gravitational attraction can be determined for any point on or above the surface from its total mass and the distance from the centre of the sphere. Provided with these two pieces of information, mass and distance, one can determine the mass of a second object from what it weighs at a specified distance from another object of known mass.

Some of this is explained scrolling down in the link I provided earlier. . . http://www.explorator...onh/weight/index.html

[ludwig]

Hi, can someone explain why planets etc stay in a constant orbit and not slowly spiral towards the thing they're orbiting.

[mibn2cweus]

They are falling . . . around. Otherwise they'd keep moving at a constant velocity in a straight line.
There's not much out there to slow them down. If something did decrease their orbital speed, gravity would pull them in closer and in the process accelerate them to the required orbital speed to establish a new stable orbit.
Orbits result as a balance between gravitational acceleration pulling inward and angular momentum aka "centrifugal force", pushing outward.

In the case of the Moon, orbital distance is actually increasing. The rotation of the Earth, being somewhat in line with and in the direction of its orbit is pulling the Moon slightly forward with tidal forces, accelerating its orbital speed and thereby nudging it gradually into a higher orbit.

Golly, I hope we're not wandering to far off topic here . . . http://en.wikipedia.o...s_of_Moon.27s_gravity