# Rotation and centrifugal force

1. Dec 20, 2014

### Scheuerf

what is the cause of the centrifugal force from the perspective of the rotating observer? Also is rotation relative like linear motion?

2. Dec 20, 2014

### OldEngr63

Centrifugal force is never actually a force (it has no 3rd law reaction). It is always a mass x acceleration term.

Yes, rotation is relative like linear motion.

3. Dec 20, 2014

### Staff: Mentor

Rotation is not relative. You can unambiguously determine how fast a reference frame is rotating without reference to any other frame. For example, you can use a gimbaled gyroscope or a ring interferometer.

4. Dec 20, 2014

### FactChecker

It's easiest to consider rotation to be absolute by considering the universe to be stationary. But Einstein did not like that any coordinate system was preferred over another. Consider the example of a person on a merry-go-round. Einstein's General Relativity Theory allows us to consider the entire universe to be rotating around a stationary merry-go-round. His theory creates a distortion of space that pulls objects away from the center of the merry-go-round. (I believe this has only been calculated with a greatly simplified model of the universe.) This is very satisfying theoretically, but it is not a practical way of looking at rotation.