Static/thermodynamic - expresses a fluid’s temperature or internal energy, e.g. from ideal gas law \(\longrightarrow\) \(p_{static}=nk_bT\)

Hydrostatic - expresses a fluid’s depth \(\longrightarrow\) \(p_{hydrostatic}=\rho gh\)

Dynamic - expresses a fluid’s velocity \(\longrightarrow\) \(p_{dynamic}={1 \over 2} \rho u^2\)

Stagnation - the pressure that would be reached if flow is brought to rest frictionlessly \(\longrightarrow\) \(p_{stagnation} = p_{static} + p_{dynamic}\)

Total - sum of all components of pressure \(\longrightarrow\) \(p_{total} = p_{static} + p_{dynamic} + p_{hydrostatic}\)

Normal force per unit surface

Measured as:

• Absolute (relative to vacuum)

• Relative (relative to atmosphere)

The relationship between relative and absolute pressure is: \(p_{rel} = p_{abs} - p_{atm}\)

A curve that is instantaneously tangent to the velocity field throughout the flow field.

In unsteady flow this changes with time.

Usually generated computationally.

The trajectory of a fluid particle of fixed identity over a period of time.

In unsteady flow pathlines cannot change their time history

Usually generated experimentally.