# From where did our earth get its initial velocity ?

by Sab95
Tags: earth, initial, velocity
 P: 4 I read in a article that earth revolves around the sun at speed of 30km/s but from where did it get its velocity at the beginning..?
 P: 413 From the conservation of the angular momentum. As the interstellar cloud of gas collapses to form a protoplanetary disk, random motions of the molecules do not perfectly cancel out, causing the emergence of a preferred spin direction in the macroscale. Further collapse exaggerates this initial preferrence, as any initial angular momentum has to be conserved in a closed system. This is also the reason why all planets revolve around the sun in the same direction, and have generally the same direction of rotation on their axes. Although in that last case there's obviously more at play than that. Just look at Venus or Uranus.
 P: 4 @Bandersnatch : But how that could account into the revolution of planets.. its something related with the rotation of the planet.. how is it related with the revolution..?? thats the part i cant understand..
P: 413

## From where did our earth get its initial velocity ?

I'm not sure where lies your confusion. It's the same mechanism. Only instead of the scale of a single planet it's the whole solar system.

Here's a video showing the simulation of the process:
https://www.youtube.com/watch?v=3YmeajE-TT8

and the paper from which it's sourced:
http://arxiv.org/abs/1010.1489
 PF Patron Sci Advisor Thanks Emeritus P: 38,400 Your question implies that you think it is strange that the rotation is not exactly 0. Wouldn't it be more strange for the rotation to be exactly a predetermined number, like 0?
 P: 245 The material the earth is made of was flying around in space. Dust and gas has some random movement, something had pushed it a little etc or it just happened to move some way since the last place it came from. When it starts collecting toward some center, it is likely that it has some small net rotation around the center, ie it is not likely that for every piece of dust going one way there is one going the other way, there is some imbalance. The falling towards the center makes them speed up and the effect gets exaggerated. You may be aware of the skater speeding up when the arms are pulled in effect, which also happens with the collapsing dust.
 P: 4 yup.. now i got it.. pls stay tuned for further questions..
 P: 6 If you want to go back even further, the ultimate source for any momentum of any particle is, of course, whatever caused the big bang.

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