# Hydrostatics

## 8. Hydrostatics

8. Hydrostatics

### 8.1 Hydrostatics as a part of mechanics

8.1 Hydrostatics as a part of mechanics

**Hydrostatics**is the study of incompressible fluids that are**at rest and in equilibrium**.- Mechanics also includes the study of fluids in motion,
**fluid dynamics**, but this is one of the most complex branches of mechanics and will not be studied on this course.

### 8.2 Density

8.2 Density

**Density = mass / volume**ρ = m/V- In the SI system, density is measured in units of kilograms per cubic meter (kg/m
^{3}). - The density of water = 1000 kg/m
^{3}and the density of air = 1.2 kg/m^{3}(atmospheric pressure, 20°C).

### 8.3 Pressure

8.3 Pressure

- The application of a force over an area produces
**pressure**. - When the force is perpendicular to the surface area, the pressure equals the force divided by the area over which it acts.
**Pressure = Force / Area**P = F/A- Pressure is a
*scalar*quantity measured in N/m^{2}or pascals (Pa) in the SI system - A pressure of 1 pascal (Pa) is equivalent to a force of 1 newton acting on each square meter.
- Pressure can also be measured in atm, bars, millibars, mm Hg, psi ...
- Atmospheric pressure is surprisingly high: just over 100 kPa

### 8.4 Archimedes' and Pascal's Principles

8.4 Archimedes' and Pascal's Principles

**Archimedes' principle**: any completely or partially submerged object experiences an upthrust or buoyant force equal to the weight of the fluid displaced by the object.-
**Pascal's principle**: The pressure applied at one point in an enclosed fluid under equilibrium conditions is transmitted equally to all parts of the fluid.