Which quantity is not directly related with rotational motion

Options

A. mass
B. angular momentum
C. torque
D. moment of inertia

Answer

To determine which quantity is not directly related to rotational motion, we will analyze each of the four options given.

### Step-by-Step Solution:

1. **Identify the quantities related to rotational motion**:
- The common quantities associated with rotational motion include moment of inertia, torque, angular momentum, and angular velocity.

2. **Evaluate each option**:
- **Option 1: Mass**
- Mass is a measure of the amount of matter in an object and is primarily used in translational motion. In rotational motion, we use moment of inertia (I) as a substitute for mass. Therefore, mass is not directly related to rotational motion.
- **Option 2: Moment of Inertia (I)**
- Moment of inertia is a measure of an object's resistance to changes in its rotation. It is directly related to rotational motion, as it plays a crucial role in calculating rotational kinetic energy and torque.
- **Option 3: Torque (τ)**
- Torque is the rotational equivalent of force and is directly related to rotational motion. It is calculated using the formula τ = r × F, where r is the distance from the pivot point and F is the force applied.
- **Option 4: Angular Momentum (L)**
- Angular momentum is defined as L = Iω, where I is the moment of inertia and ω is the angular velocity. It is directly related to rotational motion.

3. **Conclusion**:
- After evaluating all the options, it is clear that **mass** (Option 1) is the quantity that is not directly related to rotational motion. The other quantities (moment of inertia, torque, and angular momentum) are all directly related to rotational motion.

### Final Answer:
The quantity that is not directly related to rotational motion is **Option 1: Mass**.