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Why plane orbits


P_Rog
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I was doing a little reading and looked and some pictures about planet orbits and other things. One thing they talked about is how they're all within one plane pretty much. I was wondering why this is, since gravity is holding it in, why wouldn't it be more spherical. If you look at dust clouds surrounding a star, they're planar, why isn't it a big sphere encompassing the planet?

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Another way you can look at it, have a rope with a ball. Spin with the rope and it goes straight out. This is kinda like the effect which causes the planets orbit although not a scientific explaination its simple and easy to understand.

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Rotation of the newly formed star causes most of the gas and materials in the area to form into a flat disk. Out of this accretion disk planets form. Thus in mature solar systems we get planets that are all on a similar plane.

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There are several reasons for the shape of the orbits, all which end up making them, for example the gravitational pull of other planets will effect your orbit, and since the planets have different lengths for one orbit around the sun, each end up causing a unique pull to each planet.

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Why plane orbits

... they're all within one plane pretty much. I was wondering why this is' date=' ...[/quote']

 

conservation of angular momentum

 

start with a spherical cloud of gas and dust

where every particle has some motion w/rt the centerpoint, say,

imagine adding up all those angularmomentums

 

the answer is very unlikely to come out exactly zero

 

only if it it is zero can the cloud simply fall together towards a point

 

if there is some substantial amount ang.mom. then the cloud can only contract to a pancake (because quantity of rotation has to be preserved, it's a law)

 

so spherical clouds almost always contract to pancakes because of a simple conservation law

 

it is as basic as conservation of energy but people dont think about it as much because you have to buy energy at the petrol station and you dont have to buy rotation, but it is still conserved (sum total not created or destroyed)

 

BTW collision (swansont mentioned) plays a role and so does radiating away energy. as cloud collapses to pancake (with some residual rotation) there will be some excess potential/kinetic energy that has to be dumped. that is not so hard to do because it can be radiated away as heat-----the heat for instance caused by collisions. but collisions do not destroy total angular momentum

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