Help with 2nd moment of inertia

In summary, when determining the moment of inertia for a beam's y-y axis that lies in the plane of the paper, it is important to clarify whether the table is referring to the second moment of area or the moment of inertia. Additionally, the definition of the x, y, and z axes can vary depending on the context and should be clearly specified.
  • #1
Einsti
1
0
If a beam's y-y axis lies in the plane of the paper, do I use Ixx or Iyy from sections table?
 
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  • #2
Einsti said:
If a beam's y-y axis lies in the plane of the paper, do I use Ixx or Iyy from sections table?
Yes.

You're going to have to provide more information.

Please use the HW template per PF Rules. We don't provide hit and run help here.
 
  • #3
If the tables have units of length to the 4th power, I think you are referring to the second moment of area, rather than the moment of inertia. Over the past 50 years, the x y and z axes associated with the longitudinal and cross sections of a beam have been variously defined by different codes, tables, textbooks and countries. You have to be clear in each case what you mean. What people mean by 'the usual configuration' can be very different in another context.
 

FAQ: Help with 2nd moment of inertia

What is the 2nd moment of inertia?

The 2nd moment of inertia, also known as the moment of inertia or rotational inertia, is a physical property that quantifies the resistance of a rigid body to rotational motion around a particular axis. It is a measure of how evenly distributed the mass of an object is around that axis.

Why is the 2nd moment of inertia important?

The 2nd moment of inertia is important because it is a crucial factor in determining the rotational behavior of an object. It is used in various engineering and physics applications, such as calculating the torque required to rotate an object, designing structures that can withstand rotational forces, and predicting how an object will behave when subjected to rotational motion.

How do you calculate the 2nd moment of inertia?

The 2nd moment of inertia can be calculated by integrating the product of an object's mass and the square of its distance from the axis of rotation. The exact formula varies depending on the shape of the object and the axis of rotation. For simple shapes, such as a rectangular or cylindrical object, there are specific equations that can be used to calculate the moment of inertia.

What factors affect the 2nd moment of inertia?

The 2nd moment of inertia is affected by several factors, including the mass and distribution of mass of the object, the shape of the object, and the axis of rotation. In general, the larger the mass and the farther away it is from the axis of rotation, the greater the moment of inertia will be.

How does the 2nd moment of inertia relate to an object's angular acceleration?

The 2nd moment of inertia is directly proportional to an object's angular acceleration, meaning that the higher the moment of inertia, the more difficult it is for an object to rotate. This is because a larger moment of inertia requires a greater torque to produce the same amount of angular acceleration. This relationship is described by the equation τ = Iα, where τ is the torque, I is the moment of inertia, and α is the angular acceleration.

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