The force of kinetic friction does not depend on

Options

A. the relative velocity of the two surfaces in contact.
B. nature of the surface in contact.
C. normal reaction on the moving body
D. all of the above

Answer

To solve the question regarding the force of kinetic friction and what it does not depend on, we can break down the reasoning step by step:

### Step 1: Understanding Kinetic Friction
Kinetic friction is the force that opposes the motion of two surfaces sliding against each other. It is represented by the equation:
\[ F_k = \mu_k \cdot N \]
where:
- \( F_k \) is the force of kinetic friction,
- \( \mu_k \) is the coefficient of kinetic friction,
- \( N \) is the normal force acting on the object.

### Step 2: Identifying Factors Affecting Kinetic Friction
From the equation, we can see that the force of kinetic friction depends on:
- The coefficient of kinetic friction (\( \mu_k \)), which is determined by the nature of the surfaces in contact.
- The normal force (\( N \)), which is influenced by the weight of the object and any additional forces acting perpendicular to the surfaces.

### Step 3: Analyzing the Options
Now, let’s analyze the options given in the question:
- **Option A**: Relative velocity of two surfaces in contact.
- **Option B**: Nature of the surfaces in contact.
- **Option C**: Normal reaction on the moving body.

From our understanding:
- The nature of the surfaces (Option B) affects the coefficient of kinetic friction, hence it does depend on this factor.
- The normal reaction (Option C) also directly influences the force of kinetic friction, as shown in the equation.
- However, the relative velocity (Option A) does not appear in the equation for kinetic friction. The magnitude of kinetic friction remains constant regardless of the relative velocity between the two surfaces.

### Step 4: Conclusion
Thus, the force of kinetic friction does not depend on the relative velocity of the two surfaces in contact.

### Final Answer
The force of kinetic friction does not depend on the **relative velocity of two surfaces in contact** (Option A).

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