Why are the tools and machine parts made of iron smeared with grease or oil ?

Explanation

### Step-by-Step Solution:

1. **Understanding the Problem**: The question asks why tools and machine parts made of iron are smeared with grease or oil. This involves understanding the properties of iron and the effects of friction.

2. **Friction and Its Effects**: When iron parts move against each other, friction occurs. Friction is the resistance that one surface or object encounters when moving over another. This resistance can lead to several issues:
- Increased energy consumption.
- Generation of heat and sound.
- Potential wear and tear on the machine parts.
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