Which of the following is a self adjusting force ?

Options

A. Static friction
B. Rolling friction
C. Sliding friction
D. Dynamic friction

Explanation

To determine which of the following is a self-adjusting force, we need to analyze the options provided: static friction, rolling friction, sliding friction, and dynamic friction.

### Step-by-Step Solution:

1. **Understanding the Concept of Self-Adjusting Force**:
- A self-adjusting force is one that can change its magnitude in response to an external applied force, without the object moving. This means that the force can increase or decrease based on the applied force until a certain limit is reached.

2. **Analyzing Static Friction**:
- Static friction acts on an object that is at rest. When an external force is applied to the object, static friction will adjust itself to match the applied force up to a maximum limit (the maximum static friction).
- For example, if you push an object with a force \( F \), static friction will exert an equal and opposite force of \( F \) until the applied force exceeds the maximum static friction, at which point the object will start to move.

3. **Analyzing Other Types of Friction**:
- **Rolling Friction**: This is the friction that occurs when an object rolls over a surface. It does not adjust itself in the same way as static friction does.
- **Sliding Friction**: This occurs when two surfaces slide against each other. While it can vary with speed and surface conditions, it does not adjust itself in the same manner as static friction.
- **Dynamic Friction**: This is the frictional force acting on an object that is already in motion. It remains relatively constant and does not self-adjust based on applied forces.

4. **Conclusion**:
- Since static friction can change its magnitude to match the applied force (up to its maximum limit) without the object moving, it is classified as a self-adjusting force.

### Final Answer:
- The correct answer is **Static Friction**.