# How can I show the sun rotates?

1. Jan 5, 2013

### 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!!

2. Jan 5, 2013

### HallsofIvy

Staff Emeritus
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.

3. Jan 5, 2013

### SecretSnow

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?

4. Jan 5, 2013

### 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.