Conservation Angular momentum

[Cawchy87]

I started reading John Wheeler's "Cosmic Catastrophe" and he talks about the conservation of angular momentum. Although he bearly gives a paragraph to the idea as i am reading i can't get it out of my head.

Question time.

Does this law tell us that there is only so much "spinning" allowed in the universe? Or is he simply telling the reader about a simple direct relation formula?

If it is the later of the two i am really puzzled why it is considered "conservation" at all.

Thanks for helping a high school student learn!

 

[bobsmith1492]

Conservation of angular momentum means that once an object is spinning, it will continue spinning unless acted on by an external moment. That is all - basically an object in motion tends to stay in motion, just rotating rather than linear motion in this case. In other words it is a special case of Newton's Second (is it second?) Law.

 

[Cawchy87]

Ah, well that is much easier than i thought it was.

But why is there a seperate law for angular motion if it is just to do with newton' second law of motion? Is there something different about angular motion?

 

[sciencewhiz]

Newton's second law is just generalized. There is both conservation of linear momentum and angular momentum.

 

[BlueKnight]

Conservation - What this means is that it can not be created or destroyed. It could only be modified. Conservation of Mass and Energy means that a Rock can not appear over your head. (it had to come from someplace)...

There are two types of changes you can do to motion.- Imagine a car going in straight line. you can Speed up or slow down changes its rate. Or you can change its direction (turn a corner). If either one of these is severe enough, it can be noticed by the passengers. (along with rude comments about spilling their drink in their lap.)

Momentum - Stopping a car at 30 miles is harder than stopping a butterfly at the same speed. Math is a little more complicated than this, but basically momentum is about the same as 1/2 Mass * (velocity)(Velocity). So the more massive or faster something is going the more oopgh when it hits you.

Angular moment - same general concept except motion has a circular or change of direction component to its formulas.

Classic Example: skater is spinning in middle of ice with arms extended. Then they "speed" up by pulling arms to chest.

Initial Angular momentum must equal final momentum. (This is what is meant by conservation)
The formula for the values of this are kinda hard to follow. But image a circle that the finger tips are tracing. The circum of this might be 26 feet. (2 * pie * lenght from center of body.) And if skater was doing 60 rpm, then the hand is moving 26 feet/second or one complete circle per second.
Now when the skater pulled their hand close, this 26 feet/second momentum had to go somewhere. But new circle for hand is 13 feet. So the momentum causes the skater rpm's to go faster.

I hope this helps