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revelation101
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can Earth revolve around the sun without rotating itself? why some planets revolve clockwise and some other anticlockwise? what decides this direction?
cephron said:Inertia decides the direction. Rather, the inertia of infalling chunks of matter when a planet forms decide the direction, and the inertia of the resulting spinning ball of matter (its angular momentum) keeps the direction
revelation101 said:Ok.But in the question i mean the revolution of planets around the sun, not the rotation of planets
It's the other way around. The cloud collapsed to a disc because it had already acquired a net angular momentum. Look at the time spans involved. The cloud was a cloud for a long time before the protosun started to form. There was plenty of time for some passing star to spin up the cloud. The collapse was very fast compared to this long span, fast enough that angular momentum was more or less conserved during that short span.Drakkith said:This is due to the conditions of the gas cloud that collapsed to form the solar system. During collapse the cloud acquired net angular momentum (aka it started to spin slowly) in a particular direction and kept this throughout the collapse.
How could it? Angular momentum is a conserved quantity. There is no change in angular momentum without an external torque.Drakkith said:Would a static cloud acquire angular momentum from the random motions of its particles during a collapse?
D H said:How could it? Angular momentum is a conserved quantity. There is no change in angular momentum without an external torque.
Drakkith said:Ah ok. I think I see now. I was thinking there was already some angular momentum in the particles, but if its purely a static cloud then everything equals out for no net angular momentum. Does that sound right?
Per the dominant hypothesis (the Solar Nebular Disk Model), it would be unlikely for the cloud to have a sizable angular momentum without some external torque. There's the angular momentum problem to consider. Our sun comprises over 99.8% of the total mass but less than 4% of the total angular momentum of the solar system. The nebular model solves this problem: Stars selectively attract those particles in the cloud that have very little angular momentum. In solving this problem, it introduces a new problem. Where does the angular momentum in the nebular cloud come from?DaveC426913 said:A large volume of gas and dust will not have a net zero angular momentum. It would be fabulously unlikely that the momentum of each of uncountably large number of molecules would add up to zero.
So any cloud that is condensing will have some. By the time it's condensed a hundredfold, and the angular momentum is preserved, the proto-system will certainly have a net rotation, no external torque required.
It is unlikely that such a nebula would be created with no angular momentum, so it is probably initially spinning slowly. Because of conservation of angular momentum, the cloud spins faster as it contracts.
In the Nebular Hypothesis, a cloud of gas and dust collapsed by gravity begins to spin faster because of angular momentum conservation
http://csep10.phys.utk.edu/astr161/lect/solarsys/nebular.html
There's a problem with this explanation: It doesn't work. It is quite likely that such a nebula would be created without any significant angular momentum. Protostars don't have much angular momentum when they first form and they shed angular momentum as they form. Most of the angular momentum is left behind in or transferred to the protoplanetary disc. Most of the protoplanetary disc is blasted away when the star ignites. The star continues to shed angular momentum as it ages. By the time the star dies there isn't much angular momentum left.Radrook said:http://csep10.phys.utk.edu/astr161/lect/solarsys/nebular.htmlIt is unlikely that such a nebula would be created with no angular momentum, so it is probably initially spinning slowly.
D H said:There's a problem with this explanation: It doesn't work. It is quite likely that such a nebula would be created without any significant angular momentum. Protostars don't have much angular momentum when they first form and they shed angular momentum as they form. Most of the angular momentum is left behind in or transferred to the protoplanetary disc. Most of the protoplanetary disc is blasted away when the star ignites. The star continues to shed angular momentum as it ages. By the time the star dies there isn't much angular momentum left.
The way around this part of the angular momentum problem is that it is highly unlikely that such a nebula doesn't gain angular momentum between the time the nebular forms and the time star formation starts. Nearby stars, collisions between nebulae, and other mechanisms can add angular momentum to the nebula.
Planet Formation
http://library.thinkquest.org/27930/planet_formation.htm
"Revolution without rotation" refers to the movement of an object or point in a circular or elliptical path without any rotational movement around its own axis.
An example of "Revolution without rotation" is the orbit of a satellite around a planet. The satellite moves in a circular or elliptical path around the planet, but does not rotate on its own axis.
Yes, "Revolution without rotation" is possible. It is commonly observed in celestial bodies such as planets, moons, and satellites.
The key difference between the two is the direction of the movement. "Revolution without rotation" refers to movement in a circular or elliptical path without rotational movement around an axis, while "Rotation without revolution" refers to rotational movement around an axis without any circular or elliptical path.
Some practical applications of "Revolution without rotation" include satellite orbits, planetary motion, and the motion of celestial bodies in the universe. It also plays a key role in understanding the laws of motion and gravity.