The limiting friction between two surfaces depends

Options

A. on the nature of two surfaces
B. proportional to normal reaction
C. independent of area of surface
D. All the above

Answer

To solve the question regarding the factors on which limiting friction between two surfaces depends, we can break it down step by step.

### Step-by-Step Solution:

1. **Understanding Limiting Friction**:
- Limiting friction is the maximum frictional force that must be overcome for an object to start moving. It is the frictional force that acts when an object is at rest and is about to be set in motion.

2. **Factors Affecting Limiting Friction**:
- The limiting friction depends on several factors, primarily:
- The nature of the surfaces in contact.
- The normal reaction force acting on the surfaces.
- It is independent of the area of contact between the surfaces.

3. **Nature of the Surfaces**:
- The coefficient of friction (μ) is a measure of how much frictional force exists between two surfaces. Different materials have different coefficients of friction. For example, rubber on concrete has a higher coefficient than ice on steel. Therefore, the limiting friction depends on the nature of the surfaces in contact.

4. **Normal Reaction Force**:
- The limiting friction is directly proportional to the normal reaction force (N). For a horizontal surface, the normal force is equal to the weight of the object (N = mg). Hence, if the normal force increases, the limiting friction also increases.

5. **Independence from Surface Area**:
- Contrary to what might be intuitively thought, the limiting friction does not depend on the area of contact between the two surfaces. This is because friction arises from the molecular interactions at the interface of the surfaces, which is not significantly affected by the area of contact.

6. **Conclusion**:
- Therefore, we can conclude that the limiting friction between two surfaces depends on:
- The nature of the surfaces (correct).
- The normal reaction force (correct).
- It is independent of the area of contact (correct).

### Final Answer:
The limiting friction between two surfaces depends on:
- The nature of the surfaces in contact.
- The normal reaction force.
- It is independent of the area of contact.