# Centrifugal force observed from inertial frame

Suppose a ball is resting on a rotating disc ( rotating about an axis through its center ). For an observer sitting on the disc, the ball will move radially outward due to centrifugal force. A second observer, standing outside ( in inertial frame ) will see the ball rotating as well as moving radially outward. This means the centrifugal force which exists in non-inertial frame can be observed in an inertial frame also.

1. Am I right?

2. This also shows that centrifugal force is 'real', contrary to the popular belief that it is 'fictitious' or 'un-real'.

3. How to find out locus of the ball as observed from an inertial frame ( combination of a circular and linear motion )?

## 1 Answer

First, in the rotating frame, the ball will not just move radially outwards, but will spiral as well, due to another fictitious Coriolis force.

For the ground observer, he will just see the ball moving in straight path with constant speed (if there are no other real external forces). He will observe neither centrifugal force nor Coriolis force.