Angular Momentum weird scenario

In summary, the conversation discusses the definition of angular momentum in pure rotation and how it can be calculated for different scenarios. It is clarified that every axis has a well-defined angular momentum and the two cases described are just special cases. The conversation ends with a request for an elaboration on the topic.
  • #1
PhysicsKid703
25
0

Homework Statement


Before anything, please address this first question:
Angular momentum, at least for pure rotation, is defined about the axis of rotation only, correct?
[/B]
We are given a wooden ring of mass M, radius R.
I place a small particle of mass M on its circumference.
Now the wooden ring is put into pure rotation.

This is a self made conceptual question so if you're wondering why it's so weird, that's why.
my questions;
a) How do we calculate Angular Momentum of the body? What do we define it about?

Because we know that
--->for a normal rigid body in pure rotation about it's axis of symmetry(which passes through COM), angular momentum is Icm*w , where Icm is moment of inertia about COM and w is angular velocity.
--->for a normal rigid body in pure rotation about any other axis of rotation other than its axis of symmetry(which still passes through COM) , angular momentum is Iaxis*w , where laxis is moment of inertia about that axis and w is again angular velocity.
(All this is obtained through ∫ dm r2w , where r in the first case is position vector of each particle from axis of rotation, and the same in the second case, right?)

The main reason I'm getting confused is that the situation in question lies somewhere in the nether:
The body is in pure rotation about its axis of symmetry, but the axis of symmetry is not passing through the com.

The Attempt at a Solution


My thoughts are this, so correct me if I'm wrong:
I have no thoughts I'm blank.
Please explain elaborately for I have lost almost all patience with angular momentum today.
 
Last edited:
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  • #2
PhysicsKid703 said:
Angular momentum, at least for pure rotation, is defined about the axis of rotation only, correct?
Every axis has a well-defined angular momentum. It does not matter which object rotates around which axis.
The two cases you describe are just special cases - you can still use them to find the contribution of the individual components, and add them.
 

1. What is angular momentum?

Angular momentum is a physical quantity that describes the rotational motion of an object. It is a vector quantity, meaning it has both magnitude and direction.

2. How is angular momentum calculated?

Angular momentum is calculated by multiplying an object's moment of inertia (a measure of its resistance to rotational motion) by its angular velocity (the rate at which it rotates).

3. What is a weird scenario involving angular momentum?

A common weird scenario involving angular momentum is the spinning ice skater paradox, where an ice skater can change their rotational speed by changing their body position without exerting any external force.

4. How does conservation of angular momentum apply in this scenario?

The conservation of angular momentum states that the total angular momentum of a system remains constant unless acted upon by an external torque. In the case of the spinning ice skater, their change in body position causes a redistribution of their mass, resulting in a change in their moment of inertia and thus their angular velocity, but the total angular momentum of the system remains constant.

5. What are some real-world applications of angular momentum?

Angular momentum has many practical applications, such as in gyroscopes used in navigation systems, in determining the stability of objects in motion, and in the design of satellites and spacecraft for stable rotation. It also plays a crucial role in the formation of planets and solar systems.

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