When two surfaces are coated with a lubricant, then they

Options

A. stick to each other
B. slide upon each other
C. roll upon each other
D. none of the these

Answer

To solve the question, "When two surfaces are coated with a lubricant, then they...," we need to analyze the effects of lubrication on the interaction between two surfaces.

### Step-by-Step Solution:

1. **Understanding Friction**:
- When two surfaces come into contact, they tend to stick due to microscopic irregularities on their surfaces. This sticking creates friction, which opposes motion.

**Hint**: Remember that friction is caused by the interlocking of surface irregularities.

2. **Role of Lubricants**:
- A lubricant is a substance that is applied between two surfaces to reduce friction. It creates a thin layer between the surfaces, allowing them to slide over each other more easily.

**Hint**: Think about how oil or grease helps in reducing the wear and tear between moving parts.

3. **Effect of Lubrication**:
- When surfaces are lubricated, the lubricant fills the gaps between the microscopic irregularities of the surfaces. This reduces the direct contact between the surfaces, thus minimizing friction.

**Hint**: Consider how a slippery surface behaves compared to a rough one.

4. **Analyzing the Options**:
- **Option A**: Stick to each other - This is incorrect because lubrication reduces sticking.
- **Option B**: Slide over each other - This is correct as lubrication allows surfaces to move past each other with less resistance.
- **Option C**: Roll over each other - This is not applicable in the context of lubrication as it typically refers to rolling motion rather than sliding.
- **Option D**: None of this - This is incorrect since we have identified a correct option.

5. **Conclusion**:
- The correct answer is **Option B: Slide over each other**. Lubricants are designed to reduce friction and facilitate smoother motion between surfaces.

### Final Answer:
When two surfaces are coated with a lubricant, they slide over each other.