Which of the following is correct

Options

A. Using ball bearings, sliding friction changes to rolling friction.
B. Lubricants decrease friction since inter molecular forces are weak in liquids.
C. Over polishing increases friction since surface adhesion increases
D. All of the above

Answer

To solve the question, we need to analyze each of the statements provided and determine their correctness.

### Step 1: Analyze Statement 1
**Statement:** Using ball bearings changes sliding friction to rolling friction.

**Explanation:**
- When ball bearings are introduced, they allow objects to roll rather than slide. This transition from sliding to rolling friction generally results in a reduction of friction because rolling friction is typically less than sliding friction.

**Conclusion:** This statement is correct.

### Step 2: Analyze Statement 2
**Statement:** Lubricants decrease friction since intermolecular forces are weakened in liquids.

**Explanation:**
- Lubricants create a film between surfaces in contact, reducing direct contact and thus minimizing friction. They also help in reducing the heat generated during motion. The statement correctly identifies that lubricants decrease friction.

**Conclusion:** This statement is correct.

### Step 3: Analyze Statement 3
**Statement:** Over-polishing increases friction since surface adhesion increases.

**Explanation:**
- Over-polishing can indeed lead to increased surface contact at a microscopic level, which increases the adhesive forces between the surfaces. As the surfaces become smoother and come into closer contact, the adhesive forces increase, leading to higher friction.

**Conclusion:** This statement is correct.

### Step 4: Analyze Statement 4
**Statement:** All of the above.

**Explanation:**
- Since all three previous statements have been determined to be correct, this statement must also be correct.

**Conclusion:** This statement is correct.

### Final Conclusion
All statements are correct, thus the answer to the question is **Option 4: All of the above**.

---