Mark the correct statements about the friction between two bodies

Options

A. static friction is always greater than the kinetic friction.
B. coefficient of static friction is always greater than the coefficient of kinetic friction
C. Limiting friction is always greater than the kinetic friction
D. Limiting friction never less than static friction.

Answer

To determine the correct statements about the friction between two bodies, we will analyze each option based on the key concepts of friction.

### Step-by-Step Solution:

1. **Understanding Frictional Force**:
- The frictional force \( f \) between two bodies is given by the formula:
\[ f = \mu \cdot N \]
where \( \mu \) is the coefficient of friction (either static or kinetic) and \( N \) is the normal reaction force.

2. **Analyzing Option 1**:
- **Statement**: "Static friction is always greater than kinetic friction."
- **Analysis**: The coefficient of static friction (\( \mu_s \)) is always greater than the coefficient of kinetic friction (\( \mu_k \)). However, static friction can vary depending on the applied force up to its maximum value (limiting friction). Once the object starts moving, kinetic friction takes over, which is generally less than the maximum static friction. Therefore, this statement is **incorrect**.

3. **Analyzing Option 2**:
- **Statement**: "The coefficient of static friction is always greater than the coefficient of kinetic friction."
- **Analysis**: This is true as per the key concept that \( \mu_s > \mu_k \). Therefore, this statement is **correct**.

4. **Analyzing Option 3**:
- **Statement**: "Limiting friction is always greater than kinetic friction."
- **Analysis**: Limiting friction is defined as the maximum value of static friction before motion occurs. Since kinetic friction is the friction acting on a moving object, it is always less than the maximum static friction. Thus, this statement is **correct**.

5. **Analyzing Option 4**:
- **Statement**: "Limiting friction is never less than static friction."
- **Analysis**: Limiting friction is the maximum static friction that can occur before motion starts. Therefore, it cannot be less than the static friction at any point before motion begins. This statement is also **correct**.

### Summary of Options:
- **Option 1**: Incorrect
- **Option 2**: Correct
- **Option 3**: Correct
- **Option 4**: Correct

### Final Answer:
The correct statements about the friction between two bodies are Options 2, 3, and 4.

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