When a disc rotates with uniform angular velocity, which of the following is not true ?

Options

A. The sense of rotation remains same
B. The orientation of the axis of rotation remain same
C. The speed of rotation is non-zero and remains same
D. The angular acceleration is non-zero and remains same

Explanation

To solve the question, we need to analyze the statements provided regarding the rotation of a disc with uniform angular velocity. Let's go through each option step by step.

### Step 1: Understand the concept of uniform angular velocity
Uniform angular velocity means that the rate of rotation of the disc does not change over time. This implies that the angular velocity (ω) is constant.

### Step 2: Analyze each option
1. **Option 1: The sense of rotation remains the same.**
- Since the disc is rotating uniformly, the direction (or sense) of rotation does not change. This statement is true.

2. **Option 2: The orientation of the axis of rotation remains the same.**
- For uniform rotation, the axis of rotation is fixed and does not change its orientation. This statement is also true.

3. **Option 3: The speed of rotation is non-zero and remains the same.**
- Uniform angular velocity implies that the speed of rotation is constant (and non-zero if it is rotating). This statement is true.

4. **Option 4: The angular acceleration is non-zero and remains the same.**
- Angular acceleration (α) is defined as the rate of change of angular velocity. Since the angular velocity is constant (uniform), the change in angular velocity (dω) is zero. Therefore, the angular acceleration α = dω/dt = 0. This statement is not true.

### Conclusion
After analyzing all the options, we find that **Option 4** is the statement that is not true when a disc rotates with uniform angular velocity.

### Final Answer
**Option 4: The angular acceleration is non-zero and remains the same.**

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