Quick Question so I can finish this homework problem.

In summary, the conversation discussed a physical pendulum problem involving a rigid rod and a string, and the speaker was having trouble calculating the rod's moment of inertia. The expert explained the parallel axis theorem and how to use it to calculate the moment of inertia, as well as an alternative method using integration. The final equation for the moment of inertia was also provided.
  • #1
moo5003
207
0
I'm doing a physical pendulum problem involving a rigid rod of .720m in length attached to a string of 1.00 meters in length. I'm supposed to find its period. I can do the problem but I'm having trouble calculating the rods moment of inertia.

Parrallel Axis Theorem:
I = Icm + MD^2

Icm = I (1 + .720) ^2, Is md^2 the same thing...? I'm a little confused on this point.
 
Physics news on Phys.org
  • #2
The parallel axis theorem basically states that if you have the moment of inertia of an object about one axis, and you want to know its moment of inertia about another, parallel axis (one which also goes through the object's center of mass), then all you have to do is add on the moment of inertia of a point particle which is the same distance from the second axis as the center of mass of your object is. That's where the MD^2 comes from in your equation, the D is the distance to the CM of the rod.

Also note that, in this case, you could easily calculate the moment of inertia by simply doing the integral:

[tex]\int_{Mass}\rho r^2 dV[/tex]

Which, for this case of a thin rod on the end of a massless string, reduces to:

[tex]\int_{1}^{1.720}\rho r^2 dr[/tex]
 
  • #3
Thanks for the help.
The moment of inertia would then equal
1/12 M(.720m)^2 + M (1.00m + .720m)^2 Right?
 

1. What is the problem asking me to do?

The problem is asking you to complete a specific task or answer a question using the given information or data.

2. Can you explain this concept or equation to me?

Yes, I can explain the concept or equation to you. Please provide me with more specific information about what you need clarification on.

3. How do I approach this problem?

To approach a problem, it is important to first understand what the problem is asking you to do. Then, you can use your knowledge and understanding of relevant concepts and equations to solve the problem step by step.

4. Can you double-check my work to make sure it is correct?

Sure, I can double-check your work. However, it is important for you to try to solve the problem on your own first and then we can review your work together to identify any mistakes.

5. What resources can I use to help me solve this problem?

There are several resources you can use to help you solve a problem, including textbooks, lecture notes, online resources, and asking for help from a teacher or tutor. It is important to use reliable and credible sources for accurate information.

Similar threads

  • Introductory Physics Homework Help
Replies
21
Views
1K
  • Introductory Physics Homework Help
Replies
5
Views
4K
  • Introductory Physics Homework Help
Replies
10
Views
717
  • Introductory Physics Homework Help
Replies
2
Views
873
  • Introductory Physics Homework Help
Replies
5
Views
2K
  • Introductory Physics Homework Help
Replies
11
Views
1K
  • Introductory Physics Homework Help
Replies
2
Views
3K
  • Introductory Physics Homework Help
Replies
10
Views
5K
  • Introductory Physics Homework Help
Replies
2
Views
1K
  • Introductory Physics Homework Help
Replies
13
Views
2K
Back
Top