Physics chapter 4 Fluids

Fg (weight)

pVg

density x volume x gravity accel

SG (specific gravity)

unitless decimal comparing density of a given fluid to that of water at 1 atm and 4C

p/1g per cm cubed

absolute pressure

Po + pgz

incident pressure + density x gravity accel x depth of object

Pgauge

P-Patm=(Po + pgz) - Patm

Abs Pressure - atmospheric pressure= (incident pressure + density x grav accel x depth) - atm pressure

Pascal’s principle

F1/A1=F2/A2

Force over area

for incompressible fluids (that can’t be reduced by any significant degree through application of pressure) a change in pressure will be transmitted undiminished to every portion of the fluid and to the walls of the containing vessel

hydraulic systems

take advantage of near-incompressibility of liquids to generate mechanical advantage; use of pascal’s principle

Archimedes’ principle

Fbuoy=pfluid x Vfluiddisplaced x g = pfluid x Vsubmerged x g

buoyant force is equal to the density of the fluid times its volume displaced times grav accel which equals density of fluid x volume submerged x grav accel

a body wholly or partially immersed in a fluid will be buoyed upwards by a force equal to the weight of the fluid it displaces

viscosity

resistance of a fluid to flow

viscous drag

nonconservative force analogous to air resistance; increased viscosity of a fluid increases this

inviscid

fluids that have no viscosity

laminar flow

smooth and orderly movement of fluid flowing parallel to each other

Q (flow rate)

= (pi x r^4 x delta P)/(8nL)

(pi x radius of tube to the fourth x pressure gradient) / (8 x viscosity x length of pipe)

Poiseuiile’s law

turbulent flow

rough and disorderly flow causing formation of eddies

eddies

swirls of fluid of varying sizes occurring typically on the downstream side of an obstacle, formed from turbulence

critical speed (vc)

(NR x n)/(pD)

reynolds number x viscosity of fluid divided by density x diameter of tube

once this is reached, turbulence may occur; it is dependent on physical properties of the fluid

streamlines

indicate pathways followed by tiny fluid elements as they move; velocity vector of a fluid particle will always be tangential to this at any point; they never cross each other

flow rate

constant for a closed system and is independent of changes in cross-sectional area

linear speed

measure of the linear displacement of fluid particles in a given amount of time

continuity equation

Q=v1A1=v2A2

tells us that fluids will flow quicker through narrow passages and slower through wider ones

Bernoulli’s equation

P1 +1/2pv1squared + pgh1 = P2 + 1/2pv2squared + pgh2

dynamic pressure

1/2pvsquared

pressure associated with movement of a fluid