3-12;Pressure/Flow/Pumps/Surface Tension Flashcards
(38 cards)
states of matter
solid=internal order and fixed atomic positions
liquids=takes shape of container, no rigidity, atoms have very strong cohesive forces that hold them together
gas=only forces exerted are due to collisions
ideal fluid
fluid is non-viscous=internal friction is negligible) and incompressible (density is constant)
pressure
exertion of force upon a surface by an object/fluid
force/area [N/m^2 or Pa]
what does the penetrating ability of an object depend on
depends on pressure, not only force since a sharper needle will require less force to produce required penetrating pressure
pressure in liquids
at rest pressure caused by liquid is proportional to depth of liquid density
how is pressure exerted in a static liquid
liquid pressure is exerted equally in all directions so that net force is 0
pascal’s principle
any change of pressure in an enclosed fluid is transmitted undiminished to all parts of the fluid
clinical applications of pascal’s principle
chronically ill patients develop decubitus ulcers/bedsores, mainly on elbows due to exertion of largest pressure = prevented by use of water mattress = P evenly distributed against every part of body in contact w/ mattress
cerebrospinal fluid = increase in P = increases P in all part of fluid so if there is a tumour, will cause an increase in P
unborn fetus protected by amniotic sac fluid = distributes forces exerted on abdominal area equally = mother cautioned against tight clothes
Eye contains enclosed fluid = blow to front of eye transmits P to backof eye = Optic nerve/retina/blood vessels injured by XS P
buoyancy
when something is being immersed in fluid appears to be lighter than it does in air
why is buoyancy needed
to provide lifting force required to float a ship on water or balloon in air
how does buoyant forces arise
due to difference in liquid pressure above and below object
Archimedes’ principle
buoyant force on submerged object = to weight of fluid displaced
he found objects weigh less under water: weight of object in air - weight when submerged = weight of water displaced = use this to determine vol of irregular shaped object and weight density by weight/vol
what does pressure in flowing liquid depend on
depends on details of flow process, uniform pressure drop due to smooth flow through uniform tube
why are there drops in pressure during flow
loss in energy due to frictional effects
laminar flow
average flow speed that is 1/2 max speed found at centre, represents min energy loss
turbulent flow
when flow speeds up past a certain critical speed or an obstruction in flow path to form eddies = causes laminar flow to break down into turbulent flow
viscosity
frictional forces that oppose flow w/i fluid
function of a pump
to increase pressure in a fluid to allow fluid to move in a desired manner to overcome system resistance
types of pumps
lift or force pump
lift=lifts liquid rather than forcing it through system, completely mechanical, relies of Patm
force=don’t rely on Patm directly, circulates liquid in a sealed closed liquid circuit
heart as a pump
the action of ventricles is a force pump, achieves XS P by contraction
Heart is 2 synchronous force pumps.
receives blood from Venous system and raises P to push it out into arterial system.
When RV expands, AV valve opens, lets venous blood flow into ventricle whilst SL valve remains closed to prevent backflow of previously pumped blood.
what causes faults in pumping action of heart
valves that have holes or don’t close properly.
if R AV Valve isn’t closed, RV contraction pumps blood back out into venous system
if SL V isn’t closed = blood backflows from Arterial system when ventricle expands
describe pressure in circulatory system
P highest when it leaves LV, lowest when enters RA.
P raised by RV to drop enter LA as low residual pressure
LV main pump = supplies P for systematic circulation through body
why is P drop greater or lesser in arterioles than across capillaries
P drop depends on Vol Flow rate and resistance, since there are more capillaries than arterioles = vol flow rate through each capillary is much smaller
why is it important to control vol flow rate of heart
to supply required oxygen and nutrients to cells
to reduce R of CS to enable body to respond to greater demands for blood during exercise w/o overburdening heart pump
EG. Moderate EX=increase blood flow rate^3 but BP only increases by small % = total R drops less than 1/2
Vigorous EX = larger fraction of blood flows to muscles = vasodilation of muscle tissue
