How can I show the sun rotates?

[SecretSnow]

Hi guys, can I say that since the sun orbits around the centre of mass of the solar system, it has angular momentum L=mvr. And since L=Iw, the sun itself will rotate about its own axis. Am I right to say that? However, conceptually speaking, is there a reason why the sun rotates?

Also, what is the purpose of the direction of angular momentum? Is it just mainly used in conservation of angular momentum? I don't understand the real application of its direction.

One very important qns when it comes to flywheel and angular momentum. I've searched for a video on YouTube and it says the angular momentum due to the torque of the weight of the fly wheel which makes it rotate vertically, is smaller than the angular momentum of the spinning flywheel, and hence it does not rotate like its dropping down that fast when it is spinning, which is what is called precession. Is this true? Why would a larger angular momentum take precedence in the overall motion? Isn't it the same as x-y 2D trajectory motion?? Thanks a lot people!

 

[HallsofIvy]

No, it does NOT follow that since an object orbits around some point that it must also rotate around its own axis. The two are not at all connected.

 

[SecretSnow]

No, it does NOT follow that since an object orbits around some point that it must also rotate around its own axis. The two are not at all connected.

Why are they not connected? In other cases, however, can I use mvr=Iw this relationship? Because generally speaking, is this relationship true?

Anyway, is there no explanation why the sun rotates? It just does so?

 

[SecretSnow]

Oh wait I noticed my error. The mvr=Iw applies to only to body's angular momentum when rotating by itself and r is the distance to cm from point.

 

[Nickie]

I can provide some information and explanations about the sun's rotation and how it relates to angular momentum.

Firstly, yes, your understanding is correct. The sun does indeed have angular momentum due to its orbital motion around the center of mass of the solar system. This angular momentum causes the sun to rotate about its own axis, just like a spinning top or a figure skater pulling in their arms to spin faster.

The reason for the sun's rotation is related to how it formed. The sun and the entire solar system formed from a collapsing cloud of gas and dust. As this cloud collapsed, it began to spin faster and faster due to conservation of angular momentum. This spinning motion is what ultimately formed the sun and the planets.

The direction of angular momentum is an important concept in physics and has several applications. One of the main uses is in conservation of angular momentum, which states that the total angular momentum of a system remains constant unless acted upon by an external torque. This concept is used in everything from understanding the motion of planets and stars to designing spacecraft and satellites.

Regarding the flywheel and precession, your understanding is also correct. The angular momentum of the spinning flywheel is greater than the angular momentum due to the torque from the weight, causing it to precess (or rotate) around a central axis instead of just falling straight down. This is due to the principle of conservation of angular momentum, where the total angular momentum of the system remains constant.

In terms of 2D trajectory motion, the concept of angular momentum still applies, but it may not be as obvious as in the case of a spinning object. In general, the larger the angular momentum, the more difficult it is to change the direction of motion. This can be seen in the example of a spinning top, where the faster it spins, the more stable it is and the harder it is to knock it over.

I hope this helps to clarify some of your questions about angular momentum and the sun's rotation. Keep exploring and asking questions!