Subtracting object MOI from assembly to get other parts MOI?

In summary, the conversation discusses the concept of finding the moment of inertia of complex objects, specifically in the context of an airplane assembly. The question is whether one can subtract the known moments of inertia to find the unknown moments of inertia, and if not, how to go about finding them. The user also mentions posting the question in the wrong area and reposting it for future problems.
  • #1
Jweck002
7
0

Homework Statement


It's been ages since I have done Moments of Inertia of complex objects! :( Can anyone help??
Say you have an assembly like an airplane and you want to just get the moment of inertia(MOI) of the tail section and you are given the Mass of whole plane,mass of tail section, moment of inertia of front section, and moment of whole plane(moments about each axis for both). Can you just subtract the MOIs of known sections to get the MOI of unknown sections? If not, how would you go about getting the unknown sections MOI from that info.

Homework Equations

The Attempt at a Solution

 
Physics news on Phys.org
  • #2
You must show us your attempt at the solution before we are allowed to help.
 
Last edited:
  • #3
Oh. Sorry I posted this question in wrong area. I don’t have a specific problem but wanted to know for future problems on exams and real world applications.
 

Related to Subtracting object MOI from assembly to get other parts MOI?

1. How is the MOI of an object subtracted from an assembly to get the MOI of other parts?

The MOI (Moment of Inertia) of an object is subtracted from an assembly by using the Parallel Axis Theorem. This theorem states that the MOI of an object about a certain axis is equal to the MOI of the object about its center of mass plus the product of its mass and the square of the distance between the two axes. So, to get the MOI of other parts in the assembly, you would need to subtract the MOI of the object from the MOI of the assembly using this theorem.

2. Is it necessary to know the MOI of each individual part in an assembly to calculate the MOI of the entire assembly?

Yes, it is necessary to know the MOI of each individual part in an assembly to accurately calculate the MOI of the entire assembly. This is because the MOI of an assembly is the sum of the MOI of all its individual parts. So, to get the MOI of the assembly, you would need to know the MOI of each individual part.

3. How does subtracting an object's MOI affect the overall MOI of an assembly?

Subtracting an object's MOI from an assembly would decrease the overall MOI of the assembly. This is because the MOI of the object being subtracted is being removed from the sum total of the assembly's MOI. This would result in a smaller MOI for the assembly as a whole.

4. Can the MOI of an object be negative?

No, the MOI of an object cannot be negative. The MOI is a measure of an object's resistance to rotational motion and is always a positive value. It can only approach zero if the object has a very small mass or if it is rotating about an axis that passes through its center of mass.

5. Are there any other methods for calculating the MOI of an assembly?

Yes, there are other methods for calculating the MOI of an assembly. One method is the Composite Bodies Method, which involves dividing the assembly into smaller composite bodies and calculating the MOI of each body separately. Another method is the Integration Method, which involves using calculus to integrate the mass distribution of an object to calculate its MOI. However, using the Parallel Axis Theorem to subtract an object's MOI from an assembly is a common and efficient method for calculating the MOI of an assembly.

Similar threads

Can You Subtract Moments of Inertia to Find the MOI of Unknown Sections?
    • Mechanical Engineering
Replies
1
Views
998
Moment of inertia of a non uniform disc
    • Introductory Physics Homework Help
Replies
9
Views
5K
Proving generality of moment of inertia
    • Introductory Physics Homework Help
Replies
4
Views
1K
Moments of inertia using parallel axis theorem
    • Introductory Physics Homework Help
Replies
2
Views
2K
Moment of Inertia of a Rod with Two Uniform Masses Attached
    • Introductory Physics Homework Help
Replies
2
Views
24K
Shear flow in thin-walled members -- Hibbeler confusion
    • Mechanical Engineering
Replies
1
Views
2K
Mass moment of inertia of an airplane about its main gear
    • Engineering and Comp Sci Homework Help
Replies
9
Views
4K
I Time derivative of the moment of inertia tensor
    • Classical Physics
Replies
5
Views
2K
Determine the mass moment of inertia of the assembly
    • Introductory Physics Homework Help
Replies
6
Views
7K
Complex Moment of Inertia Calculation
    • Introductory Physics Homework Help
Replies
4
Views
5K

Hot Threads

Recent Insights

Back
Top