Stress is a__quantity.

Options

A. scalar
B. vector
C. tensor
D. dimensionless

Explanation

To determine the nature of stress, we can analyze the definitions of scalar, vector, and tensor quantities step by step.

### Step-by-Step Solution:

1. **Understanding Scalars**:
- A scalar quantity is defined as one that has only magnitude and no direction. Examples include temperature, mass, and time.
- **Hint**: Remember that scalars can be completely described by a single numerical value.

2. **Understanding Vectors**:
- A vector quantity has both magnitude and direction. Examples include velocity, force, and displacement.
- **Hint**: Vectors are represented with arrows and can be added using the parallelogram law.

3. **Understanding Tensors**:
- A tensor is a more complex quantity that has magnitude, direction, and can also relate to multiple dimensions. Tensors can be of different orders; for example, a second-order tensor can represent stress.
- **Hint**: Tensors can transform under coordinate changes and are used to describe more complex relationships than vectors.

4. **Analyzing Stress**:
- Stress is defined as force per unit area. It has both magnitude (the amount of force) and direction (the direction in which the force is applied).
- Stress is not merely a vector because it does not combine according to the parallelogram law, which is a characteristic of vectors. Instead, stress behaves according to more complex rules, making it a tensor.
- **Hint**: Consider how stress acts on different planes within a material; it can vary depending on the orientation of the area being considered.

5. **Conclusion**:
- Since stress has both magnitude and direction and obeys the transformation laws of tensors, it is classified as a second-order tensor quantity.
- Therefore, the correct answer is that stress is a **tensor quantity**.

### Final Answer:
Stress is a **tensor quantity**.