Science a GoGo's Home Page Forums General Discussion Physics Forum Angular Momentum and Rotation/Revolutions

"Stars like the Sun spin from the original angular momentum that was there in the solar nebula from which it formed. Not only that, all orbital motion of the planets (including the spin) is due to this orginal angular momentum." http://curious.astro.cornell.edu/question.php?number=416

My humble question is why do planets, stars, galaxies, and other celestial bodies rotate? Furthermore, do all of the aforementioned objects rotate? Why is everything in a spinning state? Can someone explain in layman's terms, please.
Sincerely,

Not only do planets rotate, some of them rotate in a retrograde fashion, opposite from the rest of the solar system. I think it's possible these planets are the result of a capture of planets from another solar system that the sun may have passed through back when the solar system was being formed. Given that most of the planets rotate in the same manner as Earth, the exceptions must have either formed elsewhere and drifted into their present positions through some kind of interaction with the sun they were formed around, which must be rotating the same way, or they were formed by eddies of backwards spinning gases in the solar system when it formed. This is just my opinion, though, and I could be way off. I'm a Biologist, after all.

Amaranth: "Given that most of the planets rotate in the same manner as Earth, the exceptions must have either formed elsewhere and drifted into their present positions through some kind of interaction with the sun they were formed around, which must be rotating the same way, or they were formed by eddies of backwards spinning gases in the solar system when it formed."

As I see it, the capture from another star seems extremely unlikely for a several of reasons:

- They orbit the sun in the same plane (the ecliptic), and in the same direction, as the other planets.
- They have small obital eccentricity.
- Venus is a rocky planet within the orbit of other rocky planets, and where such a planet should be, according to the theories about our solar system's formation.
- Uranus is a gas giant within the orbit of other gas giants and, as with Venus, where such a planet should be, according to the theories about our solar system's formation.

The "eddies of backward spinning gases" is an interesting idea, but is it likely? The theory would need to account for two eddies occurring in different regions of the disc, and in the case of Uranus, on an axis 90 degrees from the ecliptic.

The popular current theory: the two exceptions, Venus and Uranus, were originally conformist but were hit by large planetoids during their early days. The rotations of the two odd-balls are particularly interesting - Venus has almost zero rotation, and Uranus is lying on its side!

"The rotations of the two odd-balls are particularly interesting - Venus has almost zero rotation, and Uranus is lying on its side!" -rede


I think I recall figuring out that a day on Venus was longer than a year on Venus!

~SA

"Why is everything in a spinning state?" -Mitth...

I've wondered about spin too. (see "spinning semiconductors..." by Fluke) on Physics forum.

Despite the ordinary explanations, I suspect we're missing something fundemental related to spin, but....

What's the spin of sub-atomic particles? Similar to macro-spin?

~SA

I'll have a go, but I don't pretend to be very clued up!

The answer is in the topic title, "angular momentum". As a gas cloud condenses under gravity, the angular momentum is conserved so that the cloud rotates faster. A popular example of this effect is that of a ballerina spinning on the spot with arms extended; when she pulls in her arms, the spin rate increases. Another way to observe this is to swing a plumb line around a post. Although the velocity of the plumb doesn't increase, the period of rotation decreases due to the decreasing orbit length.

Imagine a vast gas cloud, perhaps light years across, and having a very minute angular momentum. As it is gradually drawn toward its centre of gravity, the rate of rotation will increase and will continue to do so until the forces of gravity and angular momentum are balanced - by which time a disc configuration will have been formed.

I've been searching the net for information about non-rotation galaxies, but all I've found so far are professional papers available only to a fee-paying membership.
______

While we're on the subject it might be worth mentioning Mach's Principle, as interpreted by Einstein.

The general idea is that, according relativity theory, does the train arrive at the station, or does the station arrive at the train? Einstein said that both are equally true. Taking another look at that, what about a rotating object? Does the object rotate, or does the rest of the universe orbit around the object? Both, again, must be equally true. Mach's Principle, according to Einstein accounts for a "centrifugal force" as a gravito-magnetic effect induced by the surrounding universe.

But maybe this is another topic...

heres my two cents:

when this universe formed , gasses massed together and they began to have centralized gravity.

there began movement of these masses toward each other due to their gravitational pulls on each other , they approached each other and rotation began as they passed each other and through each other and some were accelerated in different or opposite rotations.

there were collisions upon collisions that caused rotation.

I doubt that a single galaxy exist that has no rotation.

if there did exist one the stars in that galaxy had no outward force that could hold them in any type of orbit , and they went in and this would have resulted in a black hole without a galaxy.

so to give a short answer to your question.

Gravity caused rotation.