Moment of inertia of a point mass

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Discussion Overview

The discussion revolves around the concept of moment of inertia for a point mass, specifically focusing on the definition and implications of the variable "r," which represents the distance from the axis of rotation. The scope includes conceptual clarification and technical explanation.

Discussion Character

  • Conceptual clarification, Technical explanation

Main Points Raised

  • One participant asks for clarification on the meaning of "r" in the formula I = m * r^2, indicating confusion about its significance.
  • Another participant confirms that "r" is a distance expressed in units of length, specifically meters in the SI system.
  • A different participant attempts to clarify the relationship between the axis of rotation and the point mass, emphasizing that "r" is the distance from the axis to the mass.
  • Another contribution states that the moment of inertia of a point mass is defined as the product of mass and the square of the distance from the axis of rotation.
  • One participant notes that the moment of inertia must be referenced to a specific point or axis, mentioning that it is minimized when the reference is through the center of mass (CM) and stating that it is zero for a point mass.

Areas of Agreement / Disagreement

Participants express varying levels of understanding about the concept of moment of inertia and the role of "r." While some clarifications are made, there is no consensus on the implications or applications of the moment of inertia for a point mass.

Contextual Notes

Some statements may depend on specific definitions of moment of inertia and the context in which it is applied, such as the reference point or axis chosen for measurement.

geekie weekie
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Hello,

This is a very basic question. Wikipedia says moment of inertia I of a point mass m is calculated as:

I = m * r^2

Where, r is distance from the axis of rotation. What this actually mean? I mean what is an r?
 
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geekie weekie said:
Where, r is distance from the axis of rotation. What this actually mean? I mean what is an r?

It is a distance, expressed in units of length (meters in the SI).
 
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this is axis of rotation and in front ist point mass not full stop .

it's at r dist from rod

I=mr2
 
moment of inertia of a point mass with respect to an axis is the product of mass times the distance of the axis
squared.So "r" is the distance of the mass "m" from the axis of roation.
 
Moment of Inertia of an object has to be referenced to a particular point or axis. Take any object and its MI is a minimum when that reference is through the CM. For a point mass, it is Zero.
 

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