Why wheels are used at the bottom of luggage-carrying bags such as suitcases?

Explanation

### Step-by-Step Solution:

1. **Understanding the Problem**: The question asks why wheels are used in luggage-carrying bags, such as suitcases.

2. **Identifying the Weight of the Luggage**: Luggage, when packed, can become quite heavy, making it difficult to carry.

3. **Friction Types**: There are two main types of friction to consider:
- **Sliding Friction**: This occurs when an object slides over a surface. It is generally higher and requires more force to overcome.
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