Inertia and Wr^2 GD^2 and mr^2

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    Inertia
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Discussion Overview

The discussion revolves around the units for moment of inertia, particularly in the context of rotating bodies. Participants explore different unit representations and clarify the components of these units.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant lists potential units for inertia, including imperial units (Wr²), kgfm² (GD²), and kgm² (mr²), and seeks clarification on the meanings of f, G, and D.
  • Another participant asserts that mass is a measure of inertia and relates it to the ratio of force to acceleration, presenting inertia as m = f/a.
  • A clarification is made that the discussion pertains specifically to moments of inertia for rotating bodies.
  • One participant identifies Kgf (kilogram-force) as an ancient unit for force and explains that G refers to gravitational acceleration, while speculating that D might represent distance.
  • Another participant suggests using the formula I = τ/α, explaining the units involved in torque and angular acceleration, and connects it to the standard SI unit kgm².
  • A later reply confirms that D stands for diameter, indicating a resolution to that specific query.
  • One participant challenges the logic of using weight times diameter, suggesting that this approach does not lead to a correct understanding of the units.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of units and their components, with some clarifications made but no consensus reached on the overall understanding of the units for moment of inertia.

Contextual Notes

There are unresolved assumptions regarding the definitions of the units and the context in which they are applied. The discussion also reflects varying levels of familiarity with the terminology and concepts involved.

Who May Find This Useful

Individuals interested in the physics of rotational motion, particularly those studying mechanics or involved in engineering applications related to inertia and torque.

knarl
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trying to figure out units for inertia.

am I right in saying some units for inertia are?:

imperial units - not interested (Wr^2)
kgfm^2 (GD^2)
kgm^2 (mr^2)

if so, what is the f and the G and the D?

Thanks for any help.
 
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knarl said:
trying to figure out units for inertia.

am I right in saying some units for inertia are?:

imperial units - not interested (Wr^2)
kgfm^2 (GD^2)
kgm^2 (mr^2)

if so, what is the f and the G and the D?
The units are that of mass: kg, g, lb, oz. Mass is a measure of the inertia of an object - the ratio of force to acceleration. Inertia = f/a = m

AM
 
sorry, I meant moments of intertia. ie for a rotating body. It's just really the f that is putting me off.
 
That's an ancient (b4 1961) unit for force.It's Kgf=Kilogram-force...The gravitational acceleration (average) at the surface of the Earth times 1Kg.That explains G...As for D,i guess it's probably distance (?)...

The last of the 3 units presented is the correct (SI-mKgs) one.

Daniel.
 
knarl said:
sorry, I meant moments of intertia. ie for a rotating body. It's just really the f that is putting me off.
Ok. Just use [tex]I = \tau/\alpha[/tex].

Since torque is in units of force * distance or Nm, and [itex]\alpha[/itex] is [itex]rad/sec^{2}[/itex], the units are [itex]Nmsec^2[/itex] (or [itex]kgm^2[/itex] since [itex]N = kgm/sec^2[/itex]). As dexter says, kgf is kilograms force which is 1 kg x 9.8m/sec^2.

AM
 
thanks guys, I had a hunch that was what the f was. And the D is diameter.

knarl.
 
Weight times diameter doesn't make any sense...Even elimination would lead you to the correct answer.

Daniel.
 

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