# Relative object speed question

1. Aug 4, 2009

### PaulRacer

If you had a stationary hula hoop in space 186,000 miles in circumference with a seat attached to the center spinning at 60rpm with an observer watching the hoop "spin" with no reference point, would this be the same as spinning the outer hoop at 60 rpm and the central observer remaining still? My point is, does the outer hoop have to actually be spinning at the speed of light for it to be observed moving at the speed of light? My explanations always stink so I can try to clarify if necessary.

2. Aug 4, 2009

### Al68

No, it would not be the same. A similar scenario is to spin around on earth and watch the moon travel in circles with a coordinate velocity (relative to your head) greater than light speed. The speed of light limit only applies to inertial reference frames.

The hula hoop can spin at any arbitrary speed relative to an accelerated reference frame, but cannot reach the speed of light relative to an inertial reference frame.