# Problem on frame of reference in rotation

1. Jul 1, 2012

### shreyashebbar

1. The problem statement, all variables and given/known data

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?

2. Relevant equations
None

3. 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 ?

2. Jul 1, 2012

### Infinitum

Hi shreyashebbar!

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?

3. Jul 1, 2012

### D H

Staff Emeritus
Correct.

What dilemma?

4. Jul 2, 2012

### shreyashebbar

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?

5. Jul 2, 2012

### D H

Staff Emeritus
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.