Hydrostatics Flashcards
What is hydrostatics?
It describes the behaviour of fluids at rest, with the assumption that fluids are incompressible.
Note strictly speaking a fluid can be a solid gas or liquid.
What formula links pressure force and area?
Force = Pressure x Area
I.e. Pressure= Force/Area
What is Pascal’s Principle?
The angle at which fluid escapes from a container bears no relation to the direction in which the pressure is applied but leaves perpendicular to where the opening is.
It also stated that if a uniform force is applied to a fluid, this pressure gives rise to forces perpendicular to the walls of the container and forces are not
diminished at any point throughout the liquid.
I.e. Take a container full of water and apply 10N of force, throughout the container there would be 10N of force applied perpendicular to the walls of the container.
What factors affect the pressure of jets of liquid escaping from a pressurised container of liquid?
The force applied to the container (creating the pressure)
The size of the hole it is escaping from (and the number of holes)
What is Stevin’s Law?
Stevin’s Law: Describes the pressure of liquid due to gravity. His law shows that the pressure exerted by liquid at the base of a column is not due to the diameter of the column but rather due to the height.
The force of the liquid is shown by the following formula:
F = ρghA.
ρ: The density of the liquid:
g: The acceleration due to gravity
h: The height of the liquid in the column
A: The area of the column (a cross-section will show this)
How could you simplify Stevin’s Law to express it in terms of pressure?
F = ρghA
F = Pressure x Area
Pressure x Area = ρghA
Therefore: Pressure = ρgh
This demonstrates that the pressure exerted at the base of a column of liquid is dependent on the height and not the cross-sectional area of the column.
What happens to the pressure exerted by a liquid in an angled column?
Due to the column being angled the height is no longer static. As the height varies so will the pressure.
Pressure = ρgh
If the container of a column water was in the deep sea or at sea level how would this affect the overall pressure?
Overall pressure (Pa) = Patm + pgh
Therefore in the deep sea the atmospheric pressure would be much greater than at sea level
What is the formula for work?
Work = Force x distance
Combining the laws of hydrostatics and the formula for work explain how a hydraulic press works?
Work in = Work out
Work = force x distance
Force = Pressure x Area
A narrow column of liquid is on one side of the hydraulic press. A force is applied and the column of liquid moves down. (As a liquid does not compress)
Work in = F1 x D1
There is then a larger column of liquid on the other side. The work in will exert a force on this column of water to move it upwards.
Work out = F2 x D2
As work in = work out
F1xD1 = F2xD2
As pressure x area = force if you are given some of these values you can calculate the unknowns.
Explain why being hit in the eye may cause retinal damage?
A blow to the eye can cause more damage
than expected due to transmission of
pressure to the back of the eye.
Considering Pascal’s principle the
force exerted will distribute evenly
throughout the eye and to all areas of the retina.
