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 regarding which of the statements about friction and ball bearings is correct, we will analyze each option step by step.

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

**Explanation:** Ball bearings are small spherical objects that reduce friction between surfaces. When a wheel rotates, if it has ball bearings, the contact between the surfaces changes from sliding (where two surfaces rub against each other) to rolling (where the balls roll between the surfaces). This transition significantly reduces friction because rolling friction is generally less than sliding friction.

### Step 2: Analyze the second statement
**Statement:** Lubricants decrease friction since intermolecular forces between liquids are weak.

**Explanation:** Lubricants, such as oils or greases, are used to reduce friction between surfaces in contact. The molecules in lubricants have weaker intermolecular forces compared to solid surfaces, which allows them to flow and create a thin layer between the surfaces. This layer reduces the direct contact between the surfaces, thereby decreasing friction.

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

**Explanation:** When a surface is polished, it becomes smoother, which can initially reduce friction. However, if a surface is over-polished, it may lose its original shape and become flatter, increasing the contact area between the two surfaces. This increased contact area can lead to higher surface adhesion and, consequently, increased friction.

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

**Explanation:** Since the first three statements are true based on our analysis, the conclusion is that all the statements are correct.

### Final Answer
The correct answer is **option D: All of the above.**

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