Give examples to show that friction is both a friend and a foe.

Explanation

**Step-by-Step Solution:**

1. **Understanding Friction:**
Friction is a force that opposes the relative motion of two surfaces in contact. It can be beneficial or detrimental depending on the situation.

2. **Examples of Friction as a Friend:**
- **Walking:** When we walk, friction between our shoes and the ground prevents us from slipping. Without friction, we would not be able to walk effectively.
- **Writing:** When we write with a pen or pencil, the friction between the writing instrument and the paper allows us to leave a mark. Without sufficient friction, the pen would slip and not write properly.
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