## Mashy 3 years ago Hey.. is rotational motion relative??.. i say no cause of centrifugal force.. !.. but i read somewhere that it is :( how?

1. siddhantsharan

Suppose you and your friend are both turning in the same direction with the same angular velocity. Now, from your perspective is your friend moving? Clearly, rotational motion is relative too.

2. Carl_Pham

No, generally not, because angular motion requires acceleration, and acceleration can be measured absolutely. That is, if one observer sees a = 0, all observers will. This is not the case with a measurement of velocity, which is always relative. That is, if one observer sees v = 0, other observers may and generally will see v > 0. There is some subtlety, however, in that the universe has rotational symmetry, so that it would seem odd that if an object were entirely alone in the universe, we would be able to determine whether or not it was rotating. I think this tends to lead to subtle points in general relativity.

3. Mashy

@carl_pham.. its exactly what I was talking about.. what is SO SPECIAL if an object was ALONE in the universe?? how is its rotational motion ANY different than how it is NOW? (along with all other objects in the universe) ?

4. Mashy

@sidd .. like carl said.. even if i see that my friend is not moving RELATIVE to me.. i FOR sure know that.. we are BOTH rotating.. cause of the INERTIAL force acting on BOTH of us!