eLFH - Hydrostatics Flashcards
Hydrostatics definition
Behaviour of incompressible fluids at rest and when a force is applied to it
Definition of a fluid
A substancve than cannot exert any permanent forces tangential to a boundary
It cannot resist a shearing stress
Incompressible vs compressible fluids
Technically gases are also fluids
Gases change in volume / density considerably with pressure so are modelled as compressible fluids
Liquids have negligible changes in volume / density with pressure so are modelled as incompressible fluids
Pressure exerted on a fluid
Force is transmitted undiminished to every point of the fluid
Force acting in a column
Pressure acting in a column
Pressure at base of column does not depend on diameter of column, but on its height - area is taken out of equation for pressure
Pressure increases in linear fashion as height of column increases
Direction of forces applied within a container
Forces and pressure applies perpendicular to wall of container
Pressure applied to the bottom of a container when a pressure is applied to the top
Pressure at base = Pressure at top + pgh
Note pressure at top may be atmospheric pressure if container is open to atmosphere
Pressure at base denoted as Pa
Pressure at top denoted as Pb (which may = Patm)
Work equation
Work = Force x Distance
W = Fd
Implication of Work
In ideal system with no friction loss,
W input = W output
Therefore in a hydraulic press, heavy load can be lifted short distance by a small force travelling a larger distance
Force is also multiplied is cylinder diameter / area increases for the heavier load
Mechanisms which use the work principle
Hydraulic lifts for cars
Hydraulic brakes in cars
