Surface force

Surface force denoted fs is the force that acts across an internal or external surface element in a material body. Surface force can be decomposed into two perpendicular components: normal forces and shear forces. A normal force acts normally over an area and a shear force acts tangentially over an area.

Equations for surface force
Surface force due to pressure

\( f_{s}=p\cdot A\ \) , where f = force, p = pressure, and A = area on which a uniform pressure acts

Examples
Pressure related surface force

Since pressure is \( {\frac {force}{area}}={\mathrm {{\frac {N}{m^{2}}}}} \) , and area is a \( (length)\cdot (width)={\mathrm {m\cdot m}}={\mathrm {m^{2}}}, \)

a pressure of \( {\displaystyle 5\ \mathrm {\frac {N}{m^{2}}} =5\ \mathrm {Pa} } \) over an area of \( {\displaystyle 20\ \mathrm {m^{2}} } \) will produce a surface force of \( {\displaystyle (5\ \mathrm {Pa} )\cdot (20\ \mathrm {m^{2}} )=100\ \mathrm {N} }. \)