Friction is called a _____ evil.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for a term to fill in the blank: "Friction is called a _____ evil."

2. **Identifying the Term**: The term that fits in the blank is "necessary." Thus, the complete statement is "Friction is called a necessary evil."

3. **Explaining the Concept**:
- **Necessary**: Friction is essential for many everyday activities. For instance, it allows us to walk, as it provides the grip needed for our feet to push against the ground. Without friction, we would slip and be unable to move effectively.
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