Stress and strain are important ideas that help us understand how materials react when they are put under pressure or weight. Let's break them down simply.

Stress:

• Stress is like the pressure you feel when someone pushes on you. It tells us how much force is acting on a specific area of a material.
• We can think of it this way:
  $\text{Stress} = \frac{\text{Force}}{\text{Area}}$
  Here, stress is the pressure, force is what’s pushing, and area is the space where that force is pushing.

Strain:

• Strain is about how much a material stretches or changes shape compared to its original size.
• We can calculate it like this:
  $\text{Strain} = \frac{\text{Change in Length}}{\text{Original Length}}$
  In this formula, strain shows us how much a material has changed, while the change in length is how much it grows or shrinks.

Now, let’s talk about two types of deformation:

1. Elastic deformation happens when materials go back to their original shape after the pressure is removed. Think of a rubber band stretching and then returning to how it was.

2. Plastic deformation is when materials change shape permanently. Like when you bend a metal spoon—it stays bent even after you stop pushing.

Understanding stress and strain is really useful. It helps engineers pick the right materials for different projects!