State Hooke's law.

Explanation

**Step-by-Step Solution:**

1. **Definition of Hooke's Law**: Hooke's Law states that the strain produced in a solid material is directly proportional to the applied stress, provided the material is within its elastic limit.

2. **Understanding Stress and Strain**:
- **Stress**: It is defined as the force (F) applied per unit area (A) of the material. Mathematically, it can be expressed as:
\[
\text{Stress} = \frac{F}{A}
...