Need help understanding KE rotation

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Discussion Overview

The discussion revolves around understanding the kinetic energy of rotating objects, specifically the formula KE = (1/2)Iw^2 and its relation to linear velocity. Participants explore the meaning of the variable 'v' in the context of rotational motion and its implications when considering objects rolling down an incline.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant questions the meaning of 'v' in the kinetic energy formula, asking if it refers to initial velocity or the velocity of the center of mass.
  • Another participant points out the relation v = ωr, indicating that 'v' represents the tangential velocity of a point on the rotating body, which depends on its distance from the axis of rotation.
  • A participant inquires whether, in the case of a rotating object rolling down an incline from rest, 'v' would be the velocity of the center of mass of the object.
  • Another example is provided, discussing a wheel rolling without slipping, noting that the speed of its center relative to the surface equals the tangential speed of its rim relative to its center.

Areas of Agreement / Disagreement

Participants express varying interpretations of the variable 'v' and its implications in different scenarios, indicating that multiple views remain without a clear consensus on the definitions and applications discussed.

Contextual Notes

The discussion does not resolve the assumptions regarding the definitions of velocity in different contexts, nor does it clarify the conditions under which the relationships hold true.

Who May Find This Useful

Readers interested in the concepts of rotational motion, kinetic energy, and the dynamics of rolling objects may find this discussion relevant.

kurosaki69
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i used the formula for KE rotation KE=(1/2)Iw^2 and i translated it to (1/2) v^2/r^2, but i wanted to know what does the v in the equation stand for. is it initial velocity or velocity of center of mass. if its is the velocity of center of mass can u tell me how to solve for it
 
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Whether you know it or not, you made use of the relation [itex]v = \omega r[/itex], where v is the tangential velocity of some point on the rotating body and r is its distance from the axis.
 
ok thanks a lot my other question is what if the rotating object was rolling down a incline and it started at rest. would the velocity be the velocity of center mass of the object that is being rolled.
 
Let's take an example: A wheel, with radius r, rolls without slipping along some surface. The speed of its center with respect to the surface will be equal to the tangential speed of its rim with respect to its center.
 

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