Biological forces, mechanical forces and frictional forces are the examples of:

Options

A. contact forces
B. non-contact forces
C. both (a) and (b)
D. neither (a) nor (b)

Answer

To solve the question regarding the classification of biological forces, mechanical forces, and frictional forces, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Types of Forces**:
- We need to identify what biological, mechanical, and frictional forces are. Biological forces are those exerted by living organisms (like muscular force), mechanical forces are those resulting from machines or physical systems, and frictional forces arise when two surfaces interact.

2. **Identifying Contact Forces**:
- Contact forces are forces that occur when two objects are physically touching each other. For example, when a person uses a chest expander, there is a direct contact between the hands and the expander.

3. **Analyzing Each Force**:
- **Biological Forces**: These are contact forces as they involve the muscular force exerted by living beings (e.g., a person pushing or pulling something).
- **Mechanical Forces**: These can also be contact forces when machines or engines exert force through direct contact with objects (e.g., a car engine pushing the car forward).
- **Frictional Forces**: These are always contact forces because they occur when two surfaces are in contact and resist motion relative to each other.

4. **Conclusion**:
- Since all three types of forces (biological, mechanical, and frictional) involve direct contact between objects, we can conclude that they are all examples of contact forces.

5. **Final Answer**:
- Therefore, the correct answer to the question is that biological forces, mechanical forces, and frictional forces are examples of **contact forces**.