Which force is an example of contact force?

Options

A. Magnetic force
B. Frictional force
C. Electrostatic force
D. Gravitational force

Answer

To determine which force is an example of a contact force, we need to analyze the different types of forces mentioned in the question: magnetic force, friction force, electrostatic force, and gravitational force.

### Step-by-Step Solution:

1. **Understanding Contact Forces**:
- Contact forces are forces that occur when two objects are in physical contact with each other. Examples include friction, tension, and normal forces.

2. **Analyzing Magnetic Force**:
- Magnetic force acts at a distance through magnetic fields. For example, two magnets can attract or repel each other without touching. Therefore, magnetic force is a **non-contact force**.

3. **Analyzing Electrostatic Force**:
- Electrostatic force arises between charged objects. Similar to magnetic force, it can act over a distance without physical contact. Hence, electrostatic force is also a **non-contact force**.

4. **Analyzing Gravitational Force**:
- Gravitational force acts between masses and also does not require physical contact. It depends on the distance between the masses. Thus, gravitational force is a **non-contact force**.

5. **Analyzing Friction Force**:
- Friction force occurs when two surfaces are in contact. It depends on the nature of the surfaces (rough or smooth) and the normal force acting between them. Since friction requires physical contact to act, it is classified as a **contact force**.

6. **Conclusion**:
- Among the options provided, the only force that is an example of a contact force is the **friction force**.

### Final Answer:
The friction force is an example of a contact force.

---