# Question about Moment of Inertia

• nevil7b
In summary, the conversation is about figuring out the moment of inertia for a steel beam that is 25 feet long and 4 inches wide. The MOI is dependent on the cross section geometry, which can be found in a supplier's catalog. The calculation requires knowing the height, web thickness, and flange sizes. Additional information such as applied load, type of room, and distance between lateral supports may also be needed.
nevil7b
Hello, everyone, I am new here and was wondering if someone could help me out in regards to a figuring out the moment of inertia for a steel beam. It is 25 feet long and 4 inches wide. How think would this beam have to be before moment of inertia? Any help with this would be extremely grateful. Thanks for your time, Bob

The MOI is going to be a function of the cross section geometry. If you look at any supplier's catalog, they should list the MOI for each size they sell. In order to calculate that number, you need to know the height, web thickness and flange sizes as well.

nevil7b: What is the applied load, and type of room? And what is the distance between lateral supports for this I-beam?

## 1. What is moment of inertia?

Moment of inertia is a measure of an object's resistance to changes in its rotational motion. It is similar to mass in linear motion and depends on the object's mass distribution and its distance from the axis of rotation.

## 2. How is moment of inertia calculated?

The moment of inertia is calculated by multiplying the mass of each particle in an object by the square of its distance from the axis of rotation and then summing up these values for all the particles in the object.

## 3. What is the difference between moment of inertia and rotational inertia?

Moment of inertia and rotational inertia are essentially the same concept, with the only difference being that moment of inertia is used to describe the rotating motion of solid objects, while rotational inertia is used for the rotating motion of point masses.

## 4. How does the moment of inertia affect an object's rotational motion?

The moment of inertia directly affects an object's rotational motion, as it determines how much torque is needed to change the object's rotational speed. Objects with a larger moment of inertia will require more torque to rotate compared to objects with a smaller moment of inertia.

## 5. How can the moment of inertia be used in practical applications?

The concept of moment of inertia is used in many practical applications, such as designing machines and vehicles that require rotational motion, calculating the stability of structures, and understanding the behavior of objects in a spinning motion.

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