In mechanics, stress ($\sigma$) is defined as the internal restoring force per unit cross-sectional area developed within a body when it is deformed by an external force. $\text{Stress}=\frac{F}{A}$

• SI Unit: Pascal ($Pa$) or $N/m^2$.
• Dimensions: $[M{L}^{-1}{T}^{-2}]$, same as pressure. Unlike pressure, stress can be tensile, compressive, or shear, depending on the direction of the applied force relative to the area.