A rotating platform for a stationary observer outside, it is

Options

A. inertial frame of reference
B. non inertial frame of reference
C. both
D. some times inertial (or) some times non inertial

Answer

To solve the question regarding the nature of a rotating platform from the perspective of a stationary observer outside it, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Frames of Reference**:
- A frame of reference is a coordinate system used to describe the position and motion of objects. It can be either inertial or non-inertial.

2. **Defining Inertial and Non-Inertial Frames**:
- An **inertial frame of reference** is one in which an object either remains at rest or moves at a constant velocity unless acted upon by a force.
- A **non-inertial frame of reference** is one that is accelerating, meaning that observers in this frame will perceive fictitious forces acting on objects (like centrifugal force in a rotating frame).

3. **Analyzing the Rotating Platform**:
- The platform is rotating about an axis, which means it is undergoing circular motion.
- For a stationary observer outside the platform, the platform appears to be in motion.

4. **Observer's Perspective**:
- Since the observer sees the platform rotating, they will notice that objects on the platform experience forces that are not present in an inertial frame. For example, an object on the edge of the rotating platform would seem to be pushed outward due to centrifugal force.

5. **Conclusion**:
- Because the observer perceives the platform as moving and experiences fictitious forces, the rotating platform is classified as a **non-inertial frame of reference**.

### Final Answer:
The correct answer is that a rotating platform for a stationary observer outside it is a **non-inertial frame of reference**.