Anonymous
Anonymous asked in Science & MathematicsAstronomy & Space · 7 years ago

# Stars, planets and large moons are round coz they formed and collapsed under the force of their own gravity?

What is the meaning of collapsing under the force of their own gravity?

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• 7 years ago

When something collaspes under the force of it's own gravity it means that the inward pull of gravity on the material surrounding the centre of gravity becomes stonger than any outward forces which were balancing it. This can happen if the mass at the centre of gravity increases causing a stronger force of gravity.

Think of it like a round ball, if the force of gravity at the centre increases, the ball becomes smaller because gravity pulls everything around it closer to the centre, packing it in.

Hope this helps.

• 7 years ago

It isn't really quite like that.

First there was a disk of gas and dust around the sun. Gradually, the disk developed little clumps of higher concentrations of gas and dust, and thanks to the force of gravity, these attracted more and more nearby material into themselves until they formed planets and moons. That's the collapsing bit - the collapse of a dust and gas cloud into concentrations, in the form of planets and moons.

The question of the roughly spherical shape is slightly separate. The collapse of the dust and gas produced far more non-rounded bodies (asteroids, for example, and the smaller moons) than quasi-spherical ones.

In each of these bodies, round or otherwise, two forces were fighting it out for supremacy. One was self-gravity, the force exerted by every grain of dust in the object on every other one. Since gravity depends on mass and the distance between the attracting bodies, more massive bodies had greater self-gravity. This self-gravity tended to make them spherical (in the absence of rotation). The reason for that in turn you can think of as being potential energy. For something to be a long way from the centre of the body, it must have a lot of potential energy. You know that from picking things up here on earth. You have to exert a force on the object to be able to pick it up against the force of gravity. By doing work on the object in picking it up, you give it potential energy. If you let go, it gives back that potential energy, by falling. The potential energy of the whole thing is at a minimum (which is the stable situation) when every art is as close to the centre of gravity as it can get. That turns out to be a sphere.

The force working the other way is the rigidity of the material of which the planets are made. If you squeeze rocks just a little, as you know, nothing happens. But if you squeeze them a great deal, as it might be under hundreds of miles of other rocks, they will behave more like putty than the rocks we know. So, if there is only a little gravity, the rigidiy of the rocks wins. If there is lots (i.e. of the moon or planet is large enough) then gravity wins, and the object becomes fairly spherical.

• 3 years ago

explanation why planets and occasional mass starts do no longer cave in to form black holes has to do with the electrons orbiting the atoms. As gravity motives be counted to get closer jointly, the repelling rigidity of the electrons enhance, and that forestalls extra cave in. For stars better than a million.4 photograph voltaic hundreds yet under 3, electrons can't put off the megastar from collapsing, yet then the neutrons get dripped out of the nuclei, exerting a clean rigidity that holds up the megastar from collapsing. If the mass exceeds 3 photograph voltaic hundreds, then even that may not artwork, and the megastar cave in right into a black hollow.

• 7 years ago

Imagine huge asteroids clashing into each other for hundreds of thousands of years, and when it stops we have these planetoids that look like deformed hunks of spinnig rock, as the planetoids go around the new star, they spin themselves, over millions of years spinning and spinning and spinning, the gravity of the planet is pulling the rock inward. The gravity pulling the rock in is the collapsing under the force of gravity part, but they re round because the force of the planetoid spinning is shaping the planetoid so it becomes round.

• Anonymous
7 years ago

Yes... think of rock as a "liquid".... like a drop of water. Under the incredible gravity and pressure present in the universe, rocks "flow".... and form round blobs in space. Our own world moves constantly - mountain ranges "breathe" up and down as magma chambers fill and empty. The hard rock beneath our feet is actually "flowing" - it's just real slow so we can't see it.