Why can't a machine be 100% efficient?

Explanation

### Step-by-Step Solution:

1. **Understanding Efficiency**:
- Efficiency of a machine is defined as the ratio of useful work output to the total work input, usually expressed as a percentage.
- Mathematically, it can be represented as:
\[ \text{Efficiency} = \left( \frac{\text{Useful Work Output}}{\text{Total Work Input}} \right) \times 100\% \]
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