What is the relationship between the moment of inertia and the length of a rod?

merlos
Messages
14
Reaction score
0
The moment of inertia about an axis along the length of a rod is zero, correct?
 
Physics news on Phys.org
merlos said:
The moment of inertia about an axis along the length of a rod is zero, correct?
Almost. If the rod has a measurable radius, it is a cylinder.
 
In all the other parts ot the problem though I considered it a rod.

Here's the problem:

Find the moment of inertia about each of the following axes for a rod that is 0.280 cm in diameter and 1.70 m long, with a mass of 5.00×10−2 kg.

A. About an axis perpendicular to the rod and passing through its center.
I = (1/12)ML^2
I = .012 kgm^2

B. About an axis perpendicular to the rod passing through one end.
I = (1/3)ML^2
I = .048 kgm^2

C. About an axis along the length of the rod.
 
merlos said:
In all the other parts ot the problem though I considered it a rod.

Here's the problem:

Find the moment of inertia about each of the following axes for a rod that is 0.280 cm in diameter and 1.70 m long, with a mass of 5.00×10−2 kg.

A. About an axis perpendicular to the rod and passing through its center.
I = (1/12)ML^2
I = .012 kgm^2

B. About an axis perpendicular to the rod passing through one end.
I = (1/3)ML^2
I = .048 kgm^2

C. About an axis along the length of the rod.
The rod has a diameter. It has a moment of inertia about the long axis.
 
So, I = (1/4)MR^2 + (1/3)ML^2 ?
 
The length of the stick--or cylinder--parallel to the axis doesn't matter, only the radius.
 
Thread 'Need help understanding this figure on energy levels'

Thread 'Need help understanding this figure on energy levels'

This figure is from "Introduction to Quantum Mechanics" by Griffiths (3rd edition). It is available to download. It is from page 142. I am hoping the usual people on this site will give me a hand understanding what is going on in the figure. After the equation (4.50) it says "It is customary to introduce the principal quantum number, ##n##, which simply orders the allowed energies, starting with 1 for the ground state. (see the figure)" I still don't understand the figure :( Here is...
View full post »
Thread 'Understanding how to "tack on" the time wiggle factor'

Thread 'Understanding how to "tack on" the time wiggle factor'

The last problem I posted on QM made it into advanced homework help, that is why I am putting it here. I am sorry for any hassle imposed on the moderators by myself. Part (a) is quite easy. We get $$\sigma_1 = 2\lambda, \mathbf{v}_1 = \begin{pmatrix} 0 \\ 0 \\ 1 \end{pmatrix} \sigma_2 = \lambda, \mathbf{v}_2 = \begin{pmatrix} 1/\sqrt{2} \\ 1/\sqrt{2} \\ 0 \end{pmatrix} \sigma_3 = -\lambda, \mathbf{v}_3 = \begin{pmatrix} 1/\sqrt{2} \\ -1/\sqrt{2} \\ 0 \end{pmatrix} $$ There are two ways...
View full post »

Similar threads

Moment of Inertia of something that rotates
Replies
15
Views
2K
Moment of inertia of a double physical pendulum
Replies
4
Views
2K
Understanding Kinetic Energy: Moment of Inertia and Rotational Motion
Replies
5
Views
2K
What is the principal moment of inertia tensor for a lamina?
Replies
2
Views
2K
Correct Use of the Parallel Axis Theorem for Moment of Inertia
Replies
2
Views
2K
Moment of Inertia of an Ammonium Molecule
Replies
3
Views
4K
B Inertia of a rolling dumbell
Replies
2
Views
631
Engineering Calculating moment of inertia about z axis
Replies
5
Views
4K
Moment of inertia of a rod bent into a square
Replies
12
Views
2K
Ball bearing cantilever system with maximal moment of inertia
Replies
16
Views
2K

Hot Threads

Recent Insights

Back
Top