Problem on frame of reference in rotation

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Homework Help Overview

The discussion revolves around the concept of frames of reference in rotational motion, particularly whether points on a rotating body appear stationary from the perspective of a rotating frame of reference.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the idea of whether points on a rotating body remain stationary relative to a rotating observer, using examples like a merry-go-round and a disc rolling without slipping.

Discussion Status

Some participants are questioning the assumptions about motion and reference frames, while others are providing examples to clarify the concepts involved. There is an ongoing exploration of how different points on a rotating object behave in relation to various frames of reference.

Contextual Notes

There are indications of confusion regarding the definitions and implications of inertial versus rotating frames of reference, as well as the dynamics of rolling motion.

shreyashebbar
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Homework Statement



I wanted to know if I consider the frame of reference as a rotating body itself, then will the points lying on the body rotating be stationary with respect to the rotating frame of reference?

Homework Equations


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The Attempt at a Solution



As per me, if I am sitting in a merry go round and my friend sitting on other side should appear stationary with respect to me as he is not changing his distance with respect to me.

Kindly help me with this dilemma ?
 
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Hi shreyashebbar! :smile:

Think about a rod rotating about one of its ends, and take the reference frame to be the out-most point. Will all the points appear stationary to you? Take the innermost point(axial), will the whole body still appear stationary in that frame?
 
shreyashebbar said:
As per me, if I am sitting in a merry go round and my friend sitting on other side should appear stationary with respect to me as he is not changing his distance with respect to me.
Correct.

Kindly help me with this dilemma ?
What dilemma?
 
Hello,
when a disc of radius r rolls without slipping by half a revolution. Well I have taken a point on the circumference of the disc which is P which makes contact with the surface. The reference frame is fixed on it. Point Q lies on the diametrically opposite end on the disc.

Hence as the disc rotates the frame of reference should also rotate and when it is turned by half the point Q will still appear on y-axis at distance of 2r.

So my dilemma is if the position vector doesn't change with respect to a point on the disc so it should appear stationary with respect to P. then how come we can say that the velocity of P with respect to ground is towards left and of Q is towards right and hence velocity of p with respect to q is twice the velocity in case of pure rolling?
 
You are confusing frames of reference here.

I suggest that you work on understanding physics from the perspective of inertial frames before you delve into using rotating frames.
 

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