________ is defined as the force exerted per unit area of a surface by air.

Options

A. Force of gravity
B. Force
C. Atmospheric pressure
D. Muscular force

Answer

To answer the question, we need to fill in the blank with the correct term that describes the force exerted per unit area of a surface by air. Let's break down the solution step by step.

### Step-by-Step Solution:

1. **Understanding the Concept**:
- The question asks for a term that describes the force exerted by air on a surface. This force is measured in relation to the area of that surface.

2. **Defining Key Terms**:
- **Force**: A push or pull exerted on an object.
- **Area**: The measure of the surface of an object, typically measured in square meters (m²).

3. **Relating Force and Area**:
- When we talk about force exerted on a surface, we are interested in how much force is applied over a specific area. This relationship is crucial in understanding pressure.

4. **Formula for Pressure**:
- Pressure is defined mathematically as:
\[ \text{Pressure} = \frac{\text{Force}}{\text{Area}} \]
- This means that pressure is the amount of force applied per unit area.

5. **Identifying the Term**:
- The specific type of pressure that is exerted by air is known as **Atmospheric Pressure**. This is the pressure exerted by the weight of air in the atmosphere.

6. **Final Answer**:
- Therefore, the blank in the question can be filled with the term **Pressure**.

### Complete Answer:
**Pressure** is defined as the force exerted per unit area of a surface by air.

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