Conservation of Angular Momentum Help

In summary, the conversation discusses the issue of factoring in both translational and rotational energy in a problem involving a ball and a bar. The question is raised as to why the rotational kinetic energy of the ball is not taken into account when solving for maximum height. The answer is that in this specific problem, there is not enough information to calculate the rotation rate of the ball, and therefore it is treated as a point mass. The conversation also touches on the lack of information regarding friction and deformation in the problem.
  • #1
Speedking96
104
0

Homework Statement


Below is the question:

upload_2014-12-13_12-18-2.png


I only have an issue with the last step of the problem. Why wouldn't you factor in the translational AND rotational energy of the ball and then solve for maximum height?
 
Physics news on Phys.org
  • #2
The translational kinetic energy of the ball is the rotational kinetic energy of a system consisting of the ball alone when using a reference axis such that the ball's radial velocity is zero.
 
  • Like
Likes Speedking96
  • #3
Speedking96 said:
Why wouldn't you factor in the translational AND rotational energy of the ball and then solve for maximum height?

In a real life problem you'd have to do that. In this problem, you have no information that would allow you to calculate a specific number for the rotation rate for the 5 kg ball. You don't know the diameters of the balls. The book expects you to treat them as "point masses".

Without considering friction or the deformation of the objects,, how could the bar impart any rotation to the 5 kg ball?
 
  • Like
Likes Speedking96
  • #4
Alright, I understand. Thank you.
 
  • #5


Thank you for your question. In situations where an object is both translating and rotating, it is important to consider the conservation of both linear momentum and angular momentum. However, in the context of this problem, we are specifically looking at the maximum height reached by the ball, which is a result of its translational motion. Therefore, we only need to consider the conservation of linear momentum in order to solve for the maximum height. This is because the rotational energy of the ball does not directly affect its vertical motion, and can be accounted for separately in the calculation of its total energy. I hope this helps clarify the reasoning behind not factoring in the rotational energy in this particular problem.
 

1. What is conservation of angular momentum?

Conservation of angular momentum is a fundamental principle in physics that states that the total angular momentum of a system remains constant, unless an external torque is applied.

2. How is angular momentum conserved?

Angular momentum is conserved through the conservation of both linear momentum and angular velocity. In other words, if the mass of a system remains constant, the product of its linear velocity and distance from the axis of rotation must remain constant in order to conserve angular momentum.

3. What is the role of torque in conservation of angular momentum?

Torque is the measure of the force that causes an object to rotate around an axis. In the context of angular momentum, torque is a necessary factor for the conservation of angular momentum. If there is no torque acting on a system, then the angular momentum of the system will remain constant.

4. What are some real-life examples of conservation of angular momentum?

One example of conservation of angular momentum is the movement of a spinning top. As the top spins, its angular momentum remains constant unless an external force, such as friction, is applied. Another example is the orbit of planets around the sun. The planets maintain constant angular momentum as they orbit, due to the conservation of angular momentum.

5. How does conservation of angular momentum relate to the Law of Inertia?

The Law of Inertia, also known as Newton's first law of motion, states that an object at rest will remain at rest and an object in motion will remain in motion unless acted upon by an external force. This law is closely related to conservation of angular momentum, as both principles state that an object will maintain its state of motion unless acted upon by an external force. In other words, angular momentum will remain constant unless an external torque is applied, just as an object will remain at rest or in motion unless acted upon by an external force.

Similar threads

  • Introductory Physics Homework Help
2
Replies
57
Views
1K
  • Introductory Physics Homework Help
Replies
8
Views
1K
  • Introductory Physics Homework Help
Replies
3
Views
463
  • Introductory Physics Homework Help
2
Replies
50
Views
3K
  • Introductory Physics Homework Help
Replies
10
Views
1K
  • Introductory Physics Homework Help
Replies
2
Views
606
  • Introductory Physics Homework Help
Replies
10
Views
803
  • Introductory Physics Homework Help
Replies
6
Views
636
  • Introductory Physics Homework Help
Replies
5
Views
761
Back
Top