How does reducing friction increase the mechanical efficiency of a compound machine?

Explanation

**Step-by-Step Solution:**

1. **Understanding Mechanical Efficiency**: Mechanical efficiency of a machine is defined as the ratio of useful work output to the total work input. It is expressed as a percentage. Higher efficiency means that more of the input work is converted into useful output work.

2. **Role of Friction in Machines**: In any machine, friction occurs between moving parts. This friction opposes the motion and consumes some of the input energy. Therefore, not all the input work is converted into useful output work.

3. **Effect of Reducing Friction**: When the friction in a machine is reduced, less energy is lost to overcoming this friction. This means that more of the input work is available to do useful work.

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