Imagine if you stretch a rubber block by pinching it. Although you applied a point load at both ends of the block, the entire cross-section of the block stretches. The *distribution of force* across the *whole cross-sectional area* is what we call *stress*.

Imagine if you stretch a rubber block by pinching it. Although you applied a point load at both ends of the block, the entire cross-section of the block stretches. The *distribution of force* across the *whole cross-sectional area* is what we call *stress*.

Normal stress occurs when the force applied is in the same direction as the stress:

- F is the normal force applied
- A is the cross-sectional area
- Pa or Pascal is the SI unit for stress
- Sign: σ is +ve when in tension, -ve when in compression

Shear stress occurs when a shear force is applied instead of a normal force:

- V is the shear force applied
- A is the cross-sectional area
- Has the same Pa unit for shear stress
- Sign: +ve or -ve does not matter for now, but will be important when we come to stress transformation

Let’s look at an example now.

Normal stress occurs when the force applied is in the same direction as the stress:

- F is the normal force applied
- A is the cross-sectional area
- Pa or Pascal is the SI unit for stress
- Sign: σ is +ve when in tension, -ve when in compression

Shear stress occurs when a shear force is applied instead of a normal force:

- V is the shear force applied
- A is the cross-sectional area
- Has the same Pa unit for shear stress
- Sign: +ve or -ve does not matter for now, but will be important when we come to stress transformation

Let’s look at an example now.