# 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: pressure and stress forces. Pressure force acts normally over an area and stress force acts tangentially over an area.

## Equations for surface force

### Surface force due to pressure

$f_s=p \cdot A \$

f = Force, p = pressure, A = cross sectional area of the moving fluid

## Examples

### Pressure related surface force

Pressure is in $\frac{force}{area}=\mathrm{\frac{N}{m^2}}$
Area is a $(length)\cdot(width) = \mathrm{m \cdot m }= \mathrm{m^2}$

Given a pressure of $5 \mathrm{\frac{N}{m^2}} = 5 \mathrm{Pa}$ and an area of $20 \mathrm{m^2}$ find the surface force due to pressure.

$5 \mathrm{Pa} \cdot 20 \mathrm{m^2} = 100 \mathrm{N}$